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In the Earth's atmosphere, greenhouse gases (GHGs) and reactive trace gases are essential components of chemistry–climate interactions. These trace gases are emitted from both natural and anthropogenic sources over terrestrial and marine regions. Air–sea exchange is the dominant process controlling the distribution of several important trace gases over remote marine regions. Although the ocean–atmosphere interface covers ~70% of the Earth's surface, the quantitative air–sea exchange of reactive trace gases is estimated over the limited oceanic regions. The production and air–sea exchange of trace gases are controlled by physical conditions at both sides of the interface and ocean biogeochemistry. The northern Indian Ocean (NIO) experiences strong seasonal monsoon winds and intense tropical cyclones. Consisting of the Arabian Sea and the Bay of Bengal, it is one of the most biologically productive regimes of the world ocean and home to the intense oxygen minimum zone (OMZ) of the Arabian Sea with dissolved oxygen concentrations. Thus, the NIO offers a unique system to investigate the air–sea exchange processes of reactive trace gases. So far, most of the studies of air–sea exchange of trace gases is focused on the Atlantic and Pacific Oceans, while studies over the northern Indian Ocean are very limited and reported mainly for CH4, CO2 and N2O. Although progress has been made in recent years, studies of air–sea exchange of reactive trace gases such as non-methane hydrocarbon (NMHCs), oxygen-, sulfur- and halogen-containing hydrocarbons remain scarce. This paper addresses the current understanding of air–sea exchange processes and fluxes of reactive trace gases, including NMHCs, dimethyl sulfide (DMS), oxygenated volatile organic compounds (OVOCs), halocarbons, carbon monoxide (CO) and ozone (O3) in the northern Indian Ocean. This review summarizes the studies on the air–sea exchange of trace gases over the northern Indian Ocean and common parametrization approaches used to estimate the air–sea flux of gases. Flux range for ethene (3–10.35 µmol m–2 d–1), isoprene (0.215–0.172 µmol m–2 d–1), acetaldehyde (–6.75–11.35 µmol m–2 d–1), acetone (–9–9 µmol m–2 d–1), DMS (0.03–41.4 µmol m–2 d–1) and CO (1.4–5.4 µmol m–2 d–1) over the NIO were summarized from various in-situ and modelling studies. The paper addresses the importance of the northern Indian Ocean apropos the production and exchange of reactive trace gases, the knowledge gaps and the future scientific scope. Additionally, it emphasizes the need for a multidisciplinary study of oceanic reactive trace gas cycling and its impact on regional atmospheric chemistry over the northern Indian Ocean. [ABSTRACT FROM AUTHOR]

The optimization of aircraft trajectories involves balancing operating costs and climate impact, which are often conflicting objectives. To achieve compromised optimal solutions, higher-level information such as preferences of decision-makers must be taken into account. This paper introduces the SolFinder 1.0 module, a decision-making tool designed to identify eco-efficient aircraft trajectories, which allow for the reduction of the flight's climate impact with limited cost penalties compared to cost-optimal solutions. SolFinder 1.0 offers flexible decision-making options that allow users to select trade-offs between different objective functions, including fuel use, flight time, NOx emissions, contrail distance, and climate impact. The module is included in the AirTraf 3.0 submodel, which optimizes trajectories under atmospheric conditions simulated by the ECHAM/MESSy Atmospheric Chemistry model. This paper focuses on the ability of the module to identify eco-efficient trajectories while solving a bi-objective optimization problem that minimizes climate impact and operating costs. SolFinder 1.0 enables users to explore trajectory properties at varying locations of the Pareto fronts without prior knowledge of the problem results and to identify solutions that limit the cost of reducing the climate impact of a single flight. [ABSTRACT FROM AUTHOR]

A scientific biography is presented as an introduction to a collection of papers by his colleagues and co-workers honouring the scientific contributions and legacy of the late Dr. Timothy J. Lee (1959–2022). Tim Lee performed highly regarded research on the methods and applications of computational quantum chemistry, particularly coupled cluster theory, and computational spectroscopy, with impacts in interstellar chemistry, aiding NASA missions, atmospheric chemistry, as well as fundamental science. His presence is deeply missed. [ABSTRACT FROM AUTHOR]

The detection of hydrogen chloride (HCl) in the atmosphere of Mars was among the primary objectives of the ExoMars Trace Gas Orbiter (TGO) mission. Its discovery using the Atmospheric Chemistry Suite mid‐infrared channel (ACS MIR) showed a distinct seasonality and possible link to dust activity. This paper is part 2 of a study investigating the link between HCl and aerosols by comparing gas measurements made with TGO to dust and water ice opacities measured with the Mars Climate Sounder (MCS). In part 1, we showed, and compared, the seasonal evolution of vertical profiles of HCl, water vapor, temperature, dust opacity, and water ice opacity over the dusty periods around perihelion (solar longitudes 180°–360°) across Mars years 34–36. In part 2, we investigated the quantitative correlations in the vertical distribution between each quantity, as well as ozone. We show that there is a strong positive correlation between HCl and water vapor, which is expected due to fast photochemical production rates for HCl when reacting with water vapor photolysis products. We also show a strong positive correlation between water vapor and temperature, but are unable to show any correlation between temperature and HCl. There are weak correlations between the opacities of dust and water ice, and dust and water vapor, but only very low correlations between dust and HCl. We close with a discussion of possible sources and sinks and that interactions between HCl and water ice are the most likely for both, given the inter‐comparison. Plain Language Summary: The ExoMars Trace Gas Orbiter (TGO) has observed three Martian dusty seasons (summer in the southern hemisphere). In mid‐2018, we made the first detection of hydrogen chloride (HCl) in the Martian atmosphere using the Atmospheric Chemistry Suite (ACS). Finding this gas, among others, was a priority of ExoMars because its primary source may be volcanic. Since then, we have observed two more dusty periods with the reappearance of HCl each time. In part 1, we presented the climatology of HCl over these three dusty periods (in Mars years 34, 35, and 36) and investigate their relationships with temperature and water vapor measured by ACS, and with airborne dust and water ice measured with the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO). In this paper, part 2, we quantify the correlations between HCl, water vapor, ozone, dust, temperature, and water ice. We show that HCl is closely correlated to water vapor, which is, in turn, correlated to temperature. There is only a very low correlation between HCl and dust or water ice, which both impact water vapor. Possible mechanisms for seasonal HCl production and destruction are discussed, concluding that the freeze‐thaw cycle of atmospheric water is most likely. Key Points: Comparison of trace gases and aerosol opacity between ACS on ExoMars TGO and MCS on MROLow correlations between HCl and the opacities of dust or water ice, but very strong correlation with water vapor and the formation of icesHCl source and sink possibilities are discussed, concluding that frost activity may be the most likely possibility for both [ABSTRACT FROM AUTHOR]

Atmospheric sensitivities (gradients), quantifying the atmospheric response to emissions or other perturbations, can provide meaningful insights on the underlying atmospheric chemistry or transport processes. Atmospheric adjoint modeling enables the calculation of receptor-oriented sensitivities of model outputs of interest to input parameters (e.g., emissions), overcoming the numerical cost of conventional (forward) modeling. The adjoint of the GEOS-Chem atmospheric chemistry-transport model is a widely used such model, but prior to v36 it lacked extensive stratospheric capabilities. Here, we present the development and evaluation of the discrete adjoint of the global chemistry-transport model (CTM) GEOS-Chem unified chemistry extension (UCX) for stratospheric applications, which extends the existing capabilities of the GEOS-Chem adjoint to enable the calculation of sensitivities that include stratospheric chemistry and interactions. This development adds 37 new tracers, 273 kinetic and photolysis reactions, an updated photolysis scheme, treatment of stratospheric aerosols, and all other features described in the original UCX paper. With this development the GEOS-Chem adjoint model is able to capture the spatial, temporal, and speciated variability in stratospheric ozone depletion processes, among other processes. We demonstrate its use by calculating 2-week sensitivities of stratospheric ozone to precursor species and show that the adjoint captures the Antarctic ozone depletion potential of active halogen species, including the chlorine activation and deactivation process. The spatial variations in the sensitivity of stratospheric ozone to NO x emissions are also described. This development expands the scope of research questions that can be addressed by allowing stratospheric interactions and feedbacks to be considered in the tropospheric sensitivity and inversion applications. [ABSTRACT FROM AUTHOR]

This work contributes to an European Monitoring and Verification Support (MVS) capacity for anthropogenic CO2 emissions. Future satellite instruments that map CO2 and NO2 from space will focus on hot-spot emissions from cities and large point sources, where CO2 emissions are accompanied by emissions of NOx. To use NOx as proxy CO2 emission, information about its atmospheric lifetime and the fraction of NOx present as NO2 is required to interpret NO2 plumes. This paper presents Large Eddy Simulations with atmospheric chemistry of four large point sources world-wide. We find that the chemical evolution of the plumes depends strongly on the amount of NOx that is emitted, next to wind speed and direction. For large NOx emissions the chemistry is pushed in a high-NOx chemical regime over a length of almost 100 km downwind of the stack location. Other plumes with lower NOx emissions show a fast transition to an intermediate NOx chemical regime, with short NOx lifetimes. Simulated NO2 columns mostly agree within 20 % with the TROPOspheric Monitoring Instrument (TROPOMI), signalling that the emissions used in the model were approximately correct. However, variability in the simulations is large, making a one-to-one comparison difficult. We find that wind speed variations should be accounted for in emission estimation methods. Moreover, results indicate that common assumptions about the NO2 lifetime (≈4 hours) and NOx: NO2 ratios (≈1.3) in simplified methods that estimate emissions from NO2 satellite data (e.g. Beirle et al., 2019) need revision. [ABSTRACT FROM AUTHOR]

We present the coupling of the Jena Scheme for Biosphere-Atmosphere Coupling in Hamburg (JSBACH) version four to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. With JSBACH, the soil water bucket model in EMAC is replaced by a diffusive hydrological transport model for soil water that includes water storage and infiltration in five soil layers, preventing too rapid soil drying and reducing biases in soil temperature and moisture. A five-layer snow scheme is implemented and phase changes of water in the soil are considered. Multiple land cover types are included to provide a state dependent surface albedo, which accounts for the absorption of solar radiation by vegetation. Plant net primary productivity, leaf area index and surface roughness are calculated according to the plant functional types. This paper provides a detailed evaluation of the coupled model based on observations and reanalysis data, including ERA5/ERA5-Land datasets, Global Precipitation Climatology Project (GPCP) data, and MODIS satellite data. In particular, land surface temperature (LST), terrestrial water storage (TWS), surface albedo (α), top of atmosphere radiation flux (RadTOA), precipitation (precip), leaf area index (LAI), fraction of absorbed photosynthetic active radiation (FaPAR) and gross primary productivity (GPP) are evaluated. The strongest correlation (r) between reanalysis data and the newly coupled model are found for LST (r = 0.985, with an average global bias of -1.546 K), α (r = 0.946, with an average global bias of -0.015) and RadTOA (r = 0.907, with an average global bias of 3.56, W m -2). Precipitation exhibits a correlation with the GPCP dataset of 0.523 and an average global bias of 0.042 mm day -1. The LAI climatology in EMAC has been substituted with a refined method for directly calculating LAI. This optimisation yields a correlation of 0.637 with observations and a global mean deviation of -0.212. FaPAR and GPP exemplify two of the many additional variables made available through JSBACH in EMAC. FaPAR and observations show a correlation of 0.663 with an average global difference of -0.223, while the correlation for GPP and observations is 0.564 and the average global difference is -0.001 kg Carbon km -1. Benefiting from the numerous added features within the simulated land system, the representation of soil moisture is improved, which is critical for vegetation modelling. This improvement can be attributed to a general increase in soil moisture and water storage in deeper soil layers, leading to a reduction in normalised root mean square error (NRMSE) and a closer alignment of simulated TWS with observations, mitigating the previously widespread problem of soil drought. The correlation of TWS and observations is 0.251 and the average global difference is 0.052 m water equivalent. We show that the numerous newly added components strongly improve the land hydrology, e.g. soil moisture, while surface parameters, which were mostly prescribed according to climatologies, remain similar. The coupling of JSBACH brings EMAC a step closer towards a holistic comprehensive Earth system model and extends its versatility. [ABSTRACT FROM AUTHOR]

Detecting trace gases such as hydrogen chloride (HCl) in Mars' atmosphere is among the primary objectives of the ExoMars Trace Gas Orbiter (TGO) mission. Terrestrially, HCl is closely associated with active volcanic activity, so its detection on Mars was expected to point to some form of active magmatism/outgassing. However, after its discovery using the mid‐infrared channel of the TGO Atmospheric Chemistry Suite (ACS MIR), a clear seasonality was observed, beginning with a sudden increase in HCl abundance from below detection limits to 1–3 ppbv in both hemispheres coincident with the start of dust activity, followed by very sudden and rapid loss at the southern autumnal equinox. In this study, we have investigated the relationship between HCl and atmospheric dust by making comparisons in the vertical distribution of gases measured with ACS and aerosols measured co‐located with the Mars Climate Sounder (MCS). This study includes HCl, water vapor, and ozone measured using ACS MIR, water vapor and temperature measured with the near infrared channel of ACS, and temperature, dust opacity, and water ice opacity measured with MCS. In part 1, we show that dust loading has a strong impact in temperature, which controls the abundance of water ice and water vapor, and that HCl is very closely linked to water activity. In part 2, we investigate the quantitative correlations between each quantity and discuss the possible source and sinks of HCl, their likelihood given the correlations, and any issues arising from them. Plain Language Summary: After four full Martian years in orbit since 2018, the ExoMars Trace Gas Orbiter (TGO) has observed three Martian dusty seasons, which occur when it is spring and summer in the southern hemisphere. The first, starting in summer 2018, featured a global dust storm (GDS) after which we made the first detection of hydrogen chloride (HCl) in the Martian atmosphere using the Atmospheric Chemistry Suite (ACS) instrument. Finding this gas was a priority of ExoMars because its presence may indicate that the planet is volcanically active. Since then, we have observed two more dusty periods without a GDS and observed the reappearance of HCl each time. Here, we present the climatology of HCl in both hemispheres over these three dusty periods (in Mars years 34, 35, and 36) and investigate their relationships with temperature and water vapor measured by ACS, and with airborne dust and water ice measured with the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO). In this paper, we examine how the vertical structure of each quantity changes over time. We show that there is a close relationship between HCl and H2O, and that both are controlled by temperature, driven by dust loading. Key Points: Comparison of trace gas abundance and aerosol extinction between Atmospheric Chemistry Suite on ExoMars TGO and Mars Climate Sounder on Mars Reconnaissance OrbiterReveal the seasonal changes in hydrogen chloride on MarsShow that dust affects atmospheric temperature, which controls water vapor abundance and ice extinction, and thus impacts HCl abundance [ABSTRACT FROM AUTHOR]

Degradation of air quality in the atmosphere is mainly caused by air pollution and represents a major health risk. Limona ketone (LK) (C9H14O, 4-acetyl-1-methyl-1-cyclohexene) is emitted by α-pinene, which is massively present in the indoor environment and a major atmospheric source of secondary organic aerosols (SOAs), and has attracted attention in the field of atmospheric chemistry. The OH-addition and H-abstraction reactions of LK by OH radicals have been investigated using M06-2X, ωB97X-D, MP2 and CCSD(T) with the 6-311+G(d,p) basis set. Its degradation channels and reactions with O2, NO and HO2 radicals have been explored using quantum chemical methods. The reaction kinetics were studied theoretically over the temperature range of 278–350 K by employing canonical variational transition state theory with the small curvature tunnelling (CVT/SCT) method for both barrierless channels and channels with barriers. The addition of OH at the C1 position of LK at the endocyclic double bond was shown to be the most favourable, with a small relative energy barrier of −7.27 kcal mol−1, and H-abstraction at the C4 position exhibited a relative energy barrier of −1.65 kcal mol−1 at the M06-2X/6-311+G(d,p) level of theory. Our calculated energy results show that the OH addition reactions are more dominant than the H-abstraction channel through electronic rearrangement. The obtained overall rate coefficient at 298 K is 4.77 × 10−10 cm3 molecule−1 s−1, which is in good agreement with the experimental rate coefficient of kOH = (1.29 ± 0.33) × 10−10 at 296 ± 2 K and ∼735 Torr determined by Atkinson et al. Addition of the OH radical at the C1 position predominates over all the other reaction channels, with a branching ratio of 56.20% at 298 K. Our theoretical results suggest that the atmospheric lifetime is ∼0.58 hours and the formation of stable product 1-(hydroperoxy-4-methylcyclohex-3-en-1-yl) ethenone is thermodynamically exothermic in nature. This work provides valuable information regarding the degradation mechanism and atmospheric fate of LK in the reaction initiated by the OH radical. [ABSTRACT FROM AUTHOR]

Atmospheric sensitivities (gradients), quantifying the atmospheric response to emissions or other perturbations, can provide meaningful insights on the underlying atmospheric chemistry or transport processes. Atmospheric adjoint modelling enables the calculation of receptor-oriented sensitivities of model outputs of interest to input parameters (e.g. emissions), overcoming the numerical cost of conventional (forward) modelling. The adjoint of the GEOS-Chem atmospheric chemistrytransport model is a widely used such model, but prior to v36 has lacked extensive stratospheric capabilities. Here, we present the development and evaluation of the discrete adjoint of the global chemistry transport model (CTM) GEOS-Chem unified chemistry extension (UCX) for stratospheric applications, which extends the existing capabilities of the GEOS-Chem adjoint to enable the calculation of sensitivities that include stratospheric chemistry and interactions. This development adds 37 new tracers, 273 kinetic and photolysis reactions, an updated photolysis scheme, treatment of stratospheric aerosols, and all other features described in the original UCX paper. With this development the GEOS-Chem adjoint model is able to capture the spatial, temporal and speciated variability in stratospheric ozone depletion processes, among other processes. We demonstrate its use by calculating two-week sensitivities of stratospheric ozone to precursor species and show that the adjoint captures the Antarctic ozone depletion potential of active halogen species, including the chlorine activation and deactivation process. The spatial variations in the sensitivity of stratospheric ozone to NOx emissions are also described. This development expands the scope of research questions that can be addressed, by allowing stratospheric interactions and feedbacks to be considered in the tropospheric sensitivity and inversion applications. [ABSTRACT FROM AUTHOR]

High energy electron precipitation from the Earth's radiation belts is important for loss from the radiation belts and atmospheric chemistry. We follow up investigations presented in Reidy et al. (2021, https://doi.org/10.1029/2020ja028410) where precipitating flux is calculated inside the field of view of the POES T0 detector using quasi‐linear theory and pitch angle diffusion coefficients (Dαα) from the British Antarctic Survey (BAS). These results showed good agreements at >30 keV for L* >5 on the dawnside but the flux were too low at higher energies. We have investigated the effect of changing parameters in the calculation of the precipitating flux to improve the results for the higher energies using comparisons of in situ flux and cold plasma measurements from GOES‐15 and RBSP. We find that the strength of the diffusion coefficients rather than the shape of the source spectrum has the biggest effect on the calculated precipitation. In particular we find decreasing the cold plasma density used in the calculation of Dαα increases the diffusion and hence the precipitation at the loss cone for the higher energies, improving our results. The method of calculating Dαα is also examined, comparing co‐located rather than averaged RBSP measurements. We find that the method itself has minimal effect but using RBSP derived Dαα improved our results over using Dαα calculated using the entire BAS wave data base; this is potentially due to better measurements of the cold plasma density from RBSP than the other spacecraft included in the BAS wave data base (e.g., THEMIS). Plain Language Summary: High energy particles trapped in the Earth's radiation belt can enter the atmosphere, known as particle precipitation, and collide with atmospheric particles, which can change the atmospheric chemistry. This input into our atmosphere is key to understanding the effects of space weather on our climate system variability but is difficult to quantify. Reidy et al. (2021, https://doi.org/10.1029/2020ja028410) calculated the precipitation that would be measured by a low‐Earth orbiting satellite using wave‐particle theory and diffusion coefficients from a radiation belt model. Diffusion coefficients describe the amount of diffusion of the trapped radiation belt particle population driven by different sources (e.g., chorus waves). Reidy et al. (2021, https://doi.org/10.1029/2020ja028410) found good agreement between the calculated and measured precipitation for lower energy particles but found there was something missing for the higher energies. This paper investigates the impact of changing certain parameters within the calculations, finding the cold plasma density to be key in improving the results at higher energies. Key Points: Decreasing the cold plasma density increases calculated electron precipitation at the higher energiesCalculated precipitation for a low Earth orbiting detector is weakly dependent on the source spectrumRBSP derived diffusion coefficients provide more diffusion for precipitating particles than those derived from a larger wave database [ABSTRACT FROM AUTHOR]

Formaldehyde (HCHO) is a key carcinogen and plays an important role in atmospheric chemistry. Both field measurements and Positive Matrix Factorization (PMF) modeling have been employed to investigate the concentrations and sources of HCHO in the Lewiston-Clarkston (LC) valley of the mountainous northwestern U.S. Different instruments were deployed to measure surface formaldehyde and other related compounds in July of 2016 and 2017. The measurements reveal that the average HCHO concentrations have significantly decreased to 2–5 ppb in the LC valley in comparison to its levels (10–20 ppb) observed in July 2006. This discovery with surface measurements deserves attention given that satellite retrievals showed an increasing long-term trend from 2005 to 2014 in total vertical column density of HCHO in the region, suggesting that satellite instruments may not adequately resolve small valleys in the mountainous region. Our PMF modeling identified four major sources of HCHO in the valley: (1) emissions from a local paper mill, (2) secondary formation and background, (3) biogenic sources, and (4) traffic. This study reveals that the emissions from the paper mill cause high HCHO spikes (6–19 ppb) in the early morning. It is found that biogenic volatile organic compounds (VOCs) in the area are influenced by national forests surrounding the region (e.g., Nez Perce-Clearwater, Umatilla, Wallowa-Whitman, and Idaho Panhandle National Forests). The results provide useful information for developing strategies to control HCHO levels and have implications for future HCHO studies in atmospheric chemistry, which affects secondary aerosols and ozone formation. [Display omitted] • Significant decadal decrease in surface HCHO was discovered in a valley in Northwest. • Surface HCHO trend in the small valley is opposite to that of satellite column data. • HCHO sources include paper mill, photochemical, biogenic and traffic influences. • Volatile organic compounds (VOCs) in the area are influenced by national forests. • The methods can be used to study sources of HCHO and other toxics in any regions. [ABSTRACT FROM AUTHOR]

Nitrous acid (HONO), a key precursor of hydroxyl radicals (OH), is one of the factors affecting atmospheric chemistry and air quality. Currently, the proposed sources of HONO are not able to fully explain observed HONO concentrations. In this study, a comprehensive field observation of HONO was conducted in the autumn of 2021 in urban Beijing. The box model using a default Master Chemical Mechanism (MCM) was unable to reproduce the observed HONO concentrations with a normalized mean bias (NMB) of −92.8%. The NMB improved to −46.1% after the inclusion of seven additional HONO formation pathways. Several factors like vehicle emission factor (1.23%) and nocturnal NO2 heterogeneous uptake coefficient on the ground surface (8.25 × 10−6) were calculated based on observational data. The enhancement factor for nocturnal NO2 heterogeneous conversion was established as a function of relative humidity (RH) and incorporated into the model, which compensated for the missing nocturnal HONO sources and well-reproduced the observed HONO concentrations, with an NMB of −5.1%. The major source of HONO at night was found to be the heterogeneous reaction of NO2 on the ground surface, contributing up to 85.6%. During the daytime, it was the homogeneous reaction of NO with OH, accounting for 41.8%. The daytime primary source of OH was mainly the photolysis of HONO, which constituted 73.6% and therefore promoted the formation of secondary pollutants and exacerbated haze events. [ABSTRACT FROM AUTHOR]

Biomass burning plays an important role in climate-forcing and atmospheric chemistry. The drivers of fire activity over the past two centuries, however, are hotly debated and fueled by poor constraints on the magnitude and trends of preindustrial fire regimes. As a powerful tracer of biomass burning, reconstructions of paleoatmospheric carbon monoxide (CO) can provide valuable information on the evolution of fire activity across the preindustrial to industrial transition. Here too, however, significant disagreements between existing CO records currently allow for opposing fire histories. In this study, we reconstruct a continuous record of Antarctic ice coreCObetween 1821 and 1995CE to overlap with direct atmospheric observations. Our record indicates that the Southern Hemisphere CO burden ([CO]) increased by 50% from a preindustrial mixing ratio of ca. 35 ppb to ca. 53 ppb by 1995 CE with more variability than allowed for by state-of-the-art chemistry-climate models, suggesting that historic CO dynamics have been not fully accounted for. Using a 6-troposphere box model, a 40 to 50% decrease in Southern Hemisphere biomass-burning emissions, coincident with unprecedented rates of early 20th century anthropogenic land-use change, is identified as a strong candidate for this mismatch. [ABSTRACT FROM AUTHOR]

The Geostationary Environment Monitoring Spectrometer (GEMS) over Asia is the first geostationary Earth orbit instrument in the virtual constellation of sensors for atmospheric chemistry and composition air quality research and applications. For the first time, the hourly observations enable studies of diurnal variation in several important trace gas and aerosol pollutants including nitrogen dioxide (NO2), which is the focus of this work. NO2 is a regulated pollutant and an indicator of anthropogenic emissions in addition to being involved in tropospheric ozone chemistry and particulate matter formation. We present new quantitative measures of NO2 tropospheric column diurnal variation which can be greater than 50 % of the column amount, especially in polluted environments. The NO2 distribution is seen to change hourly and can be quite different from what would be seen by a once-a-day low-Earth-orbit satellite observation. We use GEMS data in combination with TROPOspheric Monitoring Instrument (TROPOMI) satellite and Pandora ground-based remote sensing measurements and Multi-Scale Infrastructure for Chemistry and Aerosols (Version 0, MUSICAv0) 3D chemical transport model analysis to examine the NO2 diurnal variation in January and June 2023 over Northeast Asia and Seoul, South Korea, study regions to distinguish the different emissions, chemistry, and meteorological processes that drive the variation. Understanding the relative importance of these processes will be key to including pollutant diurnal variation in models aimed at determining true pollutant exposure levels for air quality studies. The work presented here also provides a path for investigating similar NO2 diurnal cycles in the new Earth Venture Instrument-1 Tropospheric Emissions: Monitoring Pollution (TEMPO) data over North America, and later over Europe with Sentinel-4. [ABSTRACT FROM AUTHOR]

Non-methane hydrocarbons (NMHCs) in the marine atmosphere have been studied extensively due to their important roles in regulating atmospheric chemistry and climate. However, very little is known about the distribution and sources of NMHCs in the lower atmosphere over the marginal seas of China. Herein, we characterized the atmospheric NMHCs (C2–C5) in both the coastal cities and the marginal seas of China in the spring of 2021, with a focus on identifying the sources of NMHCs in the coastal atmosphere. The NMHCs in urban atmospheres, especially alkanes, were significantly higher compared to those in the marine atmosphere, suggesting that terrestrial NMHCs may be an important reservoir/source in the marine atmosphere. A significant correlation was observed between the alkane concentrations and the distances from sampling sites to the nearest land or retention of air mass over land, indicating that alkanes in the marine atmosphere are largely influenced by terrestrial inputs through air mass transport. For alkenes, a greater impact from oceanic emissions was determined due to the lower terrestrial concentrations, short atmospheric lifetime, and substantial sea-to-air fluxes of alkenes compared to alkanes (489 ± 454 vs. 129 ± 106 nmol m -2 d -1). As suggested by the positive matrix factorization, terrestrial inputs contributed to 89 % of alkanes and 69.6 % of alkenes in Chinese marginal seas, subsequently contributing to 84 % of the ozone formation potential associated with C2–C5 NMHCs. These findings underscore the significance of terrestrial outflow in controlling the distribution and composition of atmospheric NMHCs in the marginal seas of China. [ABSTRACT FROM AUTHOR]

Tropospheric ozone is a major air pollutant and greenhouse gas. It is also the primary precursor of OH, the main tropospheric oxidant. Global atmospheric chemistry models show large differences in their simulations of tropospheric ozone budgets. Here we implement the widely used GEOS-Chem atmospheric chemistry module as an alternative to CAM-chem within the Community Earth System Model version 2 (CESM2). We compare the resulting GEOS-Chem and CAM-chem simulations of tropospheric ozone and related species within CESM2 to observations from ozonesondes, surface sites, the ATom-1 aircraft campaign over the Pacific and Atlantic, and the KORUS-AQ aircraft campaign over the Seoul Metropolitan Area. We find that GEOS-Chem and CAM-chem within CESM2 have similar tropospheric ozone budgets and concentrations usually within 5 ppb but important differences in the underlying processes including (1) photolysis scheme (no aerosol effects in CAM-chem), (2) aerosol nitrate photolysis, (3) N2O5 cloud uptake, (4) tropospheric halogen chemistry, and (5) ozone deposition to the oceans. Global tropospheric OH concentrations are the same in both models, but there are large regional differences reflecting the above processes. Carbon monoxide is lower in CAM-chem (and lower than observations), at least in part because of higher OH concentrations in the Northern Hemisphere and insufficient production from isoprene oxidation in the Southern Hemisphere. CESM2 does not scavenge water-soluble gases in convective updrafts, leading to some upper-tropospheric biases. Comparison to KORUS-AQ observations shows an overestimate of ozone above 4 km altitude in both models, which at least in GEOS-Chem is due to inadequate scavenging of particulate nitrate in convective updrafts in CESM2, leading to excessive NO production from nitrate photolysis. The KORUS-AQ comparison also suggests insufficient boundary layer mixing in CESM2. This implementation and evaluation of GEOS-Chem in CESM2 contribute to the MUSICA vision of modularizing tropospheric chemistry in Earth system models. [ABSTRACT FROM AUTHOR]

Naphthalene is the most abundant polycyclic aromatic hydrocarbon (PAH) in vehicle emissions and polluted urban areas. Its atmospheric oxidation products are oxygenated compounds that are potentially harmful for health and/or contribute to secondary organic aerosol (SOA) formation. Despite its impact on air quality, its complex structure and a lack of data mean that no detailed scheme of naphthalene gaseous oxidation for SOA formation and speciation has been established yet. This study presents the construction of the first near-explicit chemical scheme for naphthalene oxidation by OH, including kinetic and mechanistic data. The scheme redundantly represents all the classical steps of atmospheric organic chemistry (i.e., oxidation of stable species, peroxy radical formation and reaction, and alkoxy radical evolution), thus integrating fragmentation or functionalization pathways and the influence of NOx on secondary compound formation. Missing kinetic and mechanistic data were estimated using structure–activity relationships (SARs) or by analogy with existing experimental or theoretical data. The proposed chemical scheme involves 383 species (231 stable species, including 93 % of the major molar masses observed in previous experimental studies) and 484 reactions with products. A first simulation reproducing experimental oxidation in an oxidation flow reactor under high- NOx conditions shows a simulated SOA mass on the same order of magnitude as has been observed experimentally, with an error of -9 %. [ABSTRACT FROM AUTHOR]

The calculation of the radiative transfer is a key component of global circulation models. In this article, we describe the most recent updates of the radiation infrastructure in the Modular Earth Submodel System (MESSy). These updates include the implementation of the PSrad radiation scheme within the RAD submodel. Furthermore, the radiation-related submodels CLOUDOPT (for the calculation of cloud optical properties) and AEROPT (for the calculation of aerosol optical properties) have been updated and are now more flexible in order to deal with different sets of shortwave and longwave bands of radiation schemes. In the wake of these updates, a new submodel (ALBEDO), which features solar-zenith-angle-dependent albedos and a new satellite-based background (white sky) albedo, was created. All of these developments are backward compatible, and previous features of the MESSy radiation infrastructure remain available. Moreover, these developments mark an important step in the use of the ECHAM/MESSy Atmospheric Chemistry (EMAC) model, as the update of the radiation scheme was a key aspect in the development of the sixth generation of the European Centre for Medium-Range Weather Forecasts – HAMburg (ECHAM6) model from ECHAM5. The developments presented here are also aimed towards using the MESSy infrastructure with the ICOsahedral Non-hydrostatic (ICON) model as a base model. The improved infrastructure will also aid in the implementation of additional radiation schemes once this should be needed. We have optimized the set of free parameters for two general circulation model-type (GCM-type) setups for pre-industrial and present-day conditions: one with the radiation scheme that was used to date (i.e. the radiation scheme of ECHAM5) and one with the newly implemented PSrad radiation scheme. After this parameter optimization, we performed four model simulations and evaluated the corresponding model results using reanalysis and observational data. The most apparent improvements related to the updated radiation scheme are the reduced cold biases in the tropical upper troposphere and lower stratosphere and the extratropical lower stratosphere and a strengthened polar vortex. The former is also related to improved stratospheric humidity and its variability if the new radiation scheme is employed. Using the multiple radiation call capability of MESSy, we have applied the two model configurations to calculate instantaneous and stratospheric-adjusted radiative forcings related to changes in greenhouse gases. Overall, we find that for many forcing experiments the simulations with the new radiation scheme show improved radiative forcing values. This is in particular the case for methane radiative forcings, which are considerably higher when assessed with the new radiation scheme and thus in better agreement with reference values. [ABSTRACT FROM AUTHOR]

Soils are a major source of nitrogen oxides, which in the atmosphere help govern its oxidative capacity. Thus the response of soil nitric oxide (NO) emissions to forcings such as warming or forest loss has a meaningful impact on global atmospheric chemistry. We find that the soil emission rate of NO in Amazonia from a common inventory is biased low by at least an order of magnitude in comparison to tower‐based observations. Accounting for this regional bias decreases the modeled global methane lifetime by 1.4%–2.6%. In comparison, a fully deforested Amazonia, representing a 37% decrease in global emissions of isoprene, decreases methane lifetime by at most 4.6%, highlighting the sensitive response of oxidation rates to changes in emissions of NO compared to those of terpenes. Our results demonstrate that improving our understanding of soil NO emissions will yield a more accurate representation of atmospheric oxidative capacity. Plain Language Summary: Soils emit a gas called nitric oxide (NO). The amount of NO emitted from soils in tropical forests is not well known, but has been assumed to be small. We simulated how different amounts of NO emissions from soils in the Amazon impacted atmospheric chemistry. By comparing our modeled results to observations we found that NO emissions from soils in the Amazon may be between 10 and 20 times larger than the current default assumption. This matters because NO has a strong influence on the rate at which methane and other gasses are removed from the atmosphere. Therefore soil NO emissions end up impacting how long methane can last in the atmosphere, and that would have additional climate impacts. Even though soil NO emissions are smaller than other sources of NO emissions globally, we find that the amount of NO emitted in the Amazon matters a lot for how long methane can last in the atmosphere. Our results demonstrate that improving estimates of soil NO emissions is going to be necessary for making accurate estimates of how long methane and other reactive species will stay in the atmosphere. Key Points: Soil emission rates of NO in common inventories may be between 10× and 20× too low over the Amazon basinHigher soil NO over the Amazon basin alters the oxidative capacity of the atmosphere and decreases global methane lifetime by 1.4%–2.6%Global methane lifetime is more sensitive to Amazon soil NO fluxes than to the loss of terpene fluxes from total deforestation of the Amazon [ABSTRACT FROM AUTHOR]

Solar particle events (SPEs) are short-lived bursts of high-energy particles from the solar atmosphere and are widely recognized as posing significant economic risks to modern society. Most SPEs are relatively weak and have minor impacts on the Earth's environment, but historic records contain much stronger SPEs which have the potential to alter atmospheric chemistry, impacting climate and biological life. The impacts of such strong SPEs would be far more severe when the Earth's protective geomagnetic field is weak, such as during past geomagnetic excursions or reversals. Here, we model the impacts of an extreme SPE under different geomagnetic field strengths, focusing on changes in atmospheric chemistry and surface radiation using the atmosphere-ocean-chemistry-climate model SOCOL3-MPIOM and the radiation transfer model LibRadtran. Under current geomagnetic conditions, an extreme SPE would increase NOx concentrations in the polar stratosphere and mesosphere, causing reductions in extratropical stratospheric ozone lasting for about a year. In contrast, with no geomagnetic field, there would be a substantial increase in NOx throughout the entire atmosphere, resulting in severe stratospheric ozone depletion for several years. The resulting ground-level ultraviolet (UV) radiation would remain elevated for up to 6 y, leading to increases in UV index up to 20 to 25% and solar-induced DNA damage rates by 40 to 50%. The potential evolutionary impacts of past extreme SPEs remain an important question, while the risks they pose to human health in modern conditions continue to be underestimated. [ABSTRACT FROM AUTHOR]

Stratospheric aerosols play a key role in atmospheric chemistry and climate. Their particle size is a crucial factor controlling the microphysical, radiative, and chemical aerosol processes in the stratosphere. Despite its importance, available observations on aerosol particle size are rather sparse. This limits our understanding and knowledge about the mechanisms and importance of chemical and climate aerosol feedbacks. The retrieval described by provides the stratospheric particle size distribution (PSD) from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) limb observations in the tropics. This algorithm has now been improved and extended to work on the entire globe. Two PSD parameters of a unimodal lognormal PSD, the median radius and the geometric standard deviation, are retrieved between 18 and 35 km altitude from SCIAMACHY limb observations by a multiwavelength nonlinear regularized inversion. The approach assumes an aerosol particle number density profile that does not change during the retrieval. The effective Lambertian surface albedo pre-retrieved from coinciding SCIAMACHY nadir observations is integrated into the retrieval algorithm to mitigate the influence of the surface albedo on the retrieval results. The extinction coefficient and the effective radius are calculated from the PSD parameters. The aerosol characteristics from SCIAMACHY are compared with in situ balloon-borne measurements from Laramie, Wyoming, and retrievals from the satellite instruments of the Stratospheric Aerosol and Gas Experiment series (SAGE II and SAGE III) and Optical Spectrograph and InfraRed Imager System (OSIRIS). In the Northern Hemisphere, the median radius differs by less than 27 % and the geometric standard deviation by less than 11 % from both balloon-borne and SAGE III data. Differences are mainly attributed to errors in the assumed a priori number density profile. Globally, the SCIAMACHY extinction coefficient at 750 nm deviates by less than 35 % from SAGE II, SAGE III, and OSIRIS data. The effective radii from SCIAMACHY, balloon-borne measurements, and SAGE III agree within about 18 %, while the effective radius based on SAGE II measurements is systematically larger. The novel data set containing the PSD parameters, the effective radius, and the aerosol extinction coefficients at 525, 750, and 1020 nm from SCIAMACHY observations is publicly available. [ABSTRACT FROM AUTHOR]

Biogenic volatile organic compounds (BVOCs), as a crucial component that impacts atmospheric chemistry and ecological interactions with various organisms, play a significant role in the atmosphere–ecosystem relationship. However, traditional field observation methods are challenging for accurately estimating BVOC emissions in forest ecosystems with high biodiversity, leading to significant uncertainty in quantifying these compounds. To address this issue, this research proposes a workflow utilizing drone-mounted lidar and photogrammetry technologies for identifying plant species to obtain accurate BVOC emission data. By applying this workflow to a typical subtropical forest plot, the following findings were made: the drone-mounted lidar and photogrammetry modules effectively segmented trees and acquired single wood structures and images of each tree. Image recognition technology enabled relatively accurate identification of tree species, with the highest-frequency family being Euphorbiaceae. The largest cumulative isoprene emissions in the study plot were from the Myrtaceae family, while those of monoterpenes were from the Rubiaceae family. To fully leverage the estimation results of BVOC emissions directly from individual tree levels, it may be necessary for communities to establish more comprehensive tree species emission databases and models. [ABSTRACT FROM AUTHOR]

Atmospheric volatile organic compounds (VOCs) constitute a wide range of species, acting as precursors to ozone and aerosol formation. Atmospheric chemistry and transport models (CTMs) are crucial to understanding the emissions, distribution, and impacts of VOCs. Given the uncertainties in VOC emissions, lack of evaluation studies, and recent changes in emissions, this work adapts the European Monitoring and Evaluation Programme Meteorological Synthesizing Centre – West (EMEP MSC-W) CTM to evaluate emission inventories in Europe. Here we undertake the first intensive model–measurement comparison of VOCs in 2 decades. The modelled surface concentrations are evaluated both spatially and temporally, using measurements from the regular EMEP monitoring network in 2018 and 2019, as well as a 2022 campaign. To achieve this, we utilised the UK National Atmospheric Emissions Inventory to derive explicit emission profiles for individual species and employed a tracer method to produce pure concentrations that are directly comparable to observations. The degree to which the modelled and measured VOCs agree varies depending on the specific species. The model successfully captures the overall spatial and temporal variations of major alkanes (e.g. ethane, n -butane) and unsaturated species (e.g. ethene, benzene) but less so for propane, i -butane, and ethyne. This discrepancy underscores potential issues in the boundary conditions for the latter species and in their primary emissions from, in particular, the solvent and road transport sectors. Specifically, potential missing propane emissions and issues with its boundary conditions are highlighted by large model underestimations and smaller propane-to-ethane ratios compared to the measurement. Meanwhile, both the model and measurements show strong linear correlations among butane isomers and among pentane isomers, indicating common sources for these pairs of isomers. However, modelled ratios of i -butane to n -butane and i -pentane to n -pentane are approximately one-third of the measured ratios, which is largely driven by significant emissions of n -butane and n -pentane from the solvent sector. This suggests issues with the speciation profile of the solvent sector, underrepresented contributions from transport and fuel evaporation sectors in current inventories, or both. Furthermore, the modelled ethene-to-ethyne and benzene-to-ethyne ratios differ significantly from measured ratios. The different model performance strongly points to shortcomings in the spatial and temporal patterns and magnitudes of ethyne emissions, especially during winter. For OVOCs, the modelled and measured concentrations of methanal and methylglyoxal show a good agreement, despite a moderate underestimation by the model in summer. This discrepancy could be attributed to an underestimation of contributions from biogenic sources or possibly a model overestimation of their photolytic loss in summer. However, the insufficiency of suitable measurements limits the evaluation of other OVOCs. Finally, model simulations employing the CAMS inventory show slightly better agreements with measurements than those using the Centre on Emission Inventories and Projections (CEIP) inventory. This enhancement is likely due to the CAMS inventory's detailed segmentation of the road transport sector, including its associated sub-sector-specific emission profiles. Given this improvement, alongside the previously mentioned concerns about the model's biased estimations of various VOC ratios, future efforts should focus on a more detailed breakdown of dominant emission sectors (e.g. solvents) and the refinement of their speciation profiles to improve model accuracy. [ABSTRACT FROM AUTHOR]

Various fire emission estimates for southern Africa during 2019, derived with multiple burned area data sets with resolutions ranging from 500 to 20 m, are evaluated using satellite carbon monoxide (CO) observations. Southern African emissions derived from burned area generated by 20 m Sentinel‐2 satellite imagery are up to 120% higher than other estimates because small fires are better detected with a higher‐resolution satellite instrument. A comprehensive comparison between simulated and observed atmospheric CO indicates that the Sentinel‐2 burned area data significantly improves emission estimates, with up to 15% reduction in CO concentration biases in comparison to emissions based on coarser resolution burned area data. We also found that the temporal lag between emissions and atmospheric CO concentrations during the peak fire month was related to atmospheric transport. These findings emphasize the importance of utilizing higher‐resolution satellite instruments in accurately estimating emissions and understanding the impact of small fires on global climate. Plain Language Summary: We studied how much carbon monoxide (CO) was released into the air in southern Africa due to fires. To derive CO emissions we used different remotely sensed data of area burned, with varying levels of detail, from 500 to 20 m, and used these emissions in a model to mimic atmospheric transport and chemistry of CO. We found that emissions derived from the very detailed 20‐m satellite images from Sentinel‐2 produced a similar large amount of CO in the atmosphere over southern Africa as seen by CO satellite observations. This is because the smaller fires, which are harder to spot, were detected with the 20‐m burned area satellite observations. We also found that the air movement and inflow of polluted air from outside Africa impacted the peak of air pollution. Key Points: Sentinel‐2 burned area detects small fires, resulting in up to 120% higher fire emissions compared to conventional resolution estimatesImproved fuel load modeling and new emission factors yield more trustworthy fire emissions that can be evaluated with top‐down constraintsAtmospheric modeling and TROPOMI CO observations indicate a 15% bias reduction using Sentinel‐2 burned area compared with coarser fire data [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) significantly influence air quality, atmospheric chemistry, and human health. An observational study was performed at the urban site of Hangzhou, China, to analyze VOC characteristics, sources, chemical reactivities, and their impact on ozone (O3) and secondary organic aerosol (SOA) formation throughout the year 2021. During the observation period, alkanes (40.13%) emerging as the predominant VOC species. Seasonal variation in VOCs followed the order of winter (26.49 ppb) > spring (23.63 ppb) > summer (23.62 ppb) > autumn (20.47 ppb). The results of positive matrix factorization (PMF) revealed that solvent usage, combustion, and vehicle exhaust were the dominant VOC sources. Regional transport from nearby provinces also significantly contributed to VOC levels. These contributions varied seasonally, with southeastern air masses prevailing in both spring and autumn, eastern air masses impacting summer, and northwestern air masses affecting winter. The campaign-averaged value of total hydroxyl (OH) radicals was 19.08 s-1. NO2 accounted for the most significant contribution to the overall OH reactivity (39.11%), followed by VOCs (28.72%). Notable seasonal fluctuations in OH reactivity followed the order of winter (24.20 s-1) > spring (19.22 s-1) > autumn (18.07 s-1) > summer (14.86 s-1). The average ozone formation potential (OFP) for the measured VOCs was calculated as 75.54 ppb, with alkenes being the dominant contributor. The highest value was observed in spring (83.05 ppb), the lowest value was in autumn (60.43 ppb). The SOA formation potential, mainly contributed by the aromatics, was averaged as 2.92 µgm-3. Additionally, the top four SOA-contributing species across four seasons were toluene, benzene, m-xylene, and ethylbenzene. VOC-PM2.5 sensitivity analysis showed that VOCs exhibited higher sensitivity to PM2.5 on clean level (PM2.5 < 35 µgm-3) than on level with heavy pollution. Alkenes, oxygenated volatile organic compounds (OVOCs) and aromatics played significant roles in the transformations of O3 and SOA in Hangzhou. Therefore, controlling the concentrations of these species is crucial for reducing complex atmospheric pollution in the region. Overall, this study compiles scientific evidence on pollution sources in Hangzhou, providing the government with valuable information. [ABSTRACT FROM AUTHOR]

In atmospheric chemistry, the Henry's law constant (HLC) is crucial for understanding the distribution of organic compounds across gas, particle, and aqueous phases. Quantitative structure–property relationship (QSPR) models described in scientific research are generally tailored to specific groups or categories of substances and are often developed using a limited set of experimental data. This study developed a machine learning model using an extensive dataset of experimental HLCs for approximately 1100 organic compounds. Molecular descriptors calculated using alvaDesc software (v 2.0) were used to train the models. A hybrid approach was adopted for feature selection, ensuring alignment with the domain knowledge. Based on the root mean squared error (RMSE) of the training and test data after cross-validation, Gradient Boosting (GB) was selected as a model for predicting HLC. The hyperparameters of the selected model were optimized using the automated hyperparameter optimization framework Optuna. The impact of features on the target variable was assessed using the SHapley Additive exPlanations (SHAP). The optimized model demonstrated strong performance across the training, evaluation, and test datasets, achieving coefficients of determination (R2) of 0.96, 0.78, and 0.74, respectively. The developed model was used to estimate the HLC of compounds associated with carbon capture and storage (CCS) emissions and secondary organic aerosols. [ABSTRACT FROM AUTHOR]

Based on the Weather Research and Forecasting Model Coupled with Chemistry (WRF-Chem) atmospheric chemistry model, a parameterization scheme for the radioactive isotope caesium (137Cs), considering processes such as advection, turbulent diffusion, dry deposition, and wet deposition, was constructed, enabling the spatial distribution simulation of the concentration and deposition of 137Cs. The experimental simulation studies were carried out during the high emission period of the Fukushima nuclear accident (from 11 to 17 March 2011). Two sets of comparison experiments, with or without deposition, were designed, the effects of wind field and precipitation on the spatial transport and ground deposition of 137Cs were analyzed, and the influence of wind field and precipitation on 137Cs vertical transport was analyzed in detail. The results indicate that the model can accurately simulate the meteorological and 137Cs variables. On 15 March, 137Cs dispersed towards the Kanto Plain in Japan under the influence of northeastern winds. In comparison to the experiment without deposition, the concentration of 137Cs in the Fukushima area decreased by approximately 286 Bq·m−3 in the deposition experiment. Under the influence of updrafts in the non-deposition experiment, a 137Cs cloud spread upward to a maximum height of 6 km, whereas in the deposition experiment, the highest dispersion of the 137Cs cloud only reach a height of 4 km. Affected by the wind field, dry deposition is mainly distributed in Fukushima, the Kanto Plain, and their eastern ocean areas, with a maximum dry deposition of 5004.5 kBq·m−2. Wet deposition is mainly influenced by the wind field and precipitation, distributed in the surrounding areas of Fukushima, with a maximum wet deposition of 725.3 kBq·m−2. The single-station test results from the deposition experiment were better than those for the non-deposition experiment: the percentage deviations of the Tokyo, Chiba, Maebashi, and Naraha stations decreased by 61%, 69%, 46%, and 51%, respectively, and the percentage root mean square error decreased by 46%, 25%, 38%, and 48%, respectively. [ABSTRACT FROM AUTHOR]

The seasonal characteristics of air pollutant concentrations are important for understanding variations in emissions released into the air and in atmospheric chemistry. The patterns seen can be influenced by anthropogenic emissions, meteorological conditions, and the transport of pollutants over long and short distances. Whilst seasonality is well understood for some pollutants such as ozone and polycyclic aromatic hydrocarbons, it is poorly understood and under-investigated for heavy metals in particulate matter (PM). This work studies long-term datasets of heavy metals in PM from a relevant UK air quality monitoring network, demonstrating the seasonal characteristics of the concentrations of these metals for the first time. Surprisingly, both 'high in winter–low in summer' and 'low in winter–high in summer' seasonality was observed, with some metals showing little or no seasonality. The 'high in winter–low in summer' seasonality (particularly for As) is attributable to the dominant contribution being from local primary sources, such as burning process producing larger PM sizes. The 'low in winter–high in summer' seasonality (particularly for V) is attributable to weak or non-seasonal local sources being dominated by contributions from medium and long-range transport during the summer months, when pollutant transport is more efficient. The findings contribute significantly to our understanding of the seasonality of metals in PM concentrations and the role played by the long-range transport of pollutants. Conclusions are also drawn about the implications for the calculation of annual averages on compliance-based air quality networks if data from a time series of a pollutant that displays seasonal characteristics are missing. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols impact the Earth's climate system directly by scattering and absorbing solar radiation, and it is important to characterise the aerosol optical properties in detail. This study reports the development and validation of an airborne dual-wavelength cavity-attenuated phase-shift (CAPS) single monitor, named A2S2 (Aerosol Absorption Spectral Sizer), based on the commercial CAPS single-scattering albedo monitor (CAPS-PM SSA ; Aerodyne), to simultaneously measure the aerosol optical scattering and extinction at both 450 and 630 nm wavelengths. Replaced pressure and temperature sensors and an additional flow control system were incorporated into the A2S2 for its utilisation on board research aircraft measuring within the troposphere. The evaluation of A2S2 characteristics was performed in the laboratory and included the investigation of the signal-to-noise ratio, validation of performance at various pressure levels, optical closure studies and intercomparing with the currently validated techniques. The chamber experiments show that the A2S2 can perform measurements at sample pressures as low as 550 hPa and at sample temperatures as high as 315 K. Based on the Allan analysis results, we have evaluated that the minimum detection limit of the measurements shows that the measurements have a limit accuracy of ∼ 2 Mm-1 at 450 nm and ∼ 1 Mm-1 at 630 nm for 1 Hz measurements of both scattering coefficients (σsca) and extinction coefficients (σext). The optical closure study with size-selected polystyrene latex (PSL) particles shows that the truncation error of the A2S2 is negligible for particles with particle volume diameter (Dp) < 200 nm, while, for the larger sub-micrometre particles, the measurement uncertainty of A2S2 increases but remains less than 20 %. The average factors to correct the truncation error are 1.13 and 1.05 for 450 and 630 nm, respectively. A simplified truncation correction, dependent on the scattering Ångström exponent (SAE), was developed to rectify truncation errors of the future A2S2 field measurement data. The σsca and σext measured by the A2S2 show good agreement with the concurrent measured results from the nephelometer and the CAPS particle extinction monitor (CAPS-PM ex). The absorption coefficient (σabs) derived through the extinction-minus-scattering (EMS) method by the A2S2 also corresponds with the results obtained from the aethalometer. The A2S2 was successfully deployed during an aircraft measurement campaign (Atmospheric ChemistRy Of the Suburban foreSt – ACROSS) conducted in the vicinity of Paris and the surrounding regions. The average SSA measured during the entire ACROSS flight campaign is 0.86 and 0.88 at 450 and 630 nm, respectively, suggesting that light-absorbing organic aerosols play a significant role. The average SAE and absorption Ångström exponent (AAE) varied due to measurements in various pollution conditions. The results presented in this study indicate that the A2S2 instrument is reliable for measuring aerosol σsca and σext at both blue and red wavelengths, and it stands as a viable substitute for future airborne evaluations of aerosol optical properties. [ABSTRACT FROM AUTHOR]

The oxygen isotope anomaly (Δ17O = δ17O - 0.52 × δ18O > 0) has proven to be a robust tool for probing photochemical cycling and atmospheric formation pathways of oxidized reactive nitrogen (NOy). Several studies have developed modeling techniques to implicitly model Δ17O of NOy molecules based on numerous assumptions that may not always be valid. Thus, these models may be oversimplified and limit our ability to compare model Δ17O values of NOy with observations. In this work, we introduce a novel method for explicitly tracking Δ17O transfer and propagation into NOy and odd oxygen (Ox), integrated into the Regional Atmospheric Chemistry Mechanism, version 2 (RACM2). Termed ICOIN-RACM2 (InCorporating Oxygen Isotopes of NOy in RACM2), this new model includes the addition of 55 new species and 729 replicate reactions to represent the propagation of Δ17O derived from O3 into NOy and Ox. Employing this mechanism within a box model, we simulate Δ17O for various NOy and Ox molecules for chamber experiments with varying initial nitrogen oxides (NOx = NO + NO2) and α -pinene conditions, revealing response shifts in Δ17O linked to distinct oxidant conditions. Furthermore, diel cycles are simulated under two summertime scenarios, representative of an urban and rural site, revealing pronounced Δ17O diurnal patterns for several NOy components and substantial Δ17O differences associated with pollution levels (urban vs. rural). Overall, the proposed mechanism offers the potential to assess NOy oxidation chemistry in chamber studies and air quality campaigns through Δ17O model comparisons against observations. The integration of this mechanism into a 3-D atmospheric chemistry transport model is expected to notably enhance our capacity to model and anticipate Δ17O across landscapes, consequently refining model representations of atmospheric chemistry and tropospheric oxidation capacity. [ABSTRACT FROM AUTHOR]

Haze events in the North China Plain (NCP) and a decline in ozone levels in Southern Coast China (SC) from 21 January to 9 February 2020 during the COVID-19 lockdown have attracted public curiosity and scholarly attention. Most previous studies focused on the impact of atmospheric chemistry processes associated with anomalous weather elements in these cases, but fewer studies quantified the impact of various weather elements within the context of a specific weather pattern. To identify the weather patterns responsible for inducing this unexpected situation and to further quantify the importance of different meteorological factors during the haze event, two approaches are employed. These approaches implemented the comparisons of observations in 2020 with climatology averaged over the years 2015–2019 with a novel structural SOM (self-organising map) model and with the prediction of the "business as usual" (hereafter referred to as BAU) emission strength by the GBM (gradient-boosting machine) model, respectively. The results reveal that the unexpected PM 2.5 pollution and O 3 decline from the climatology in NCP and SC could be effectively explained by the presence of a double-centre high-pressure system across China. Moreover, the GBM results provided a quantitative assessment of the importance of each meteorological factor in driving the predictions of PM 2.5 and O 3 under the specific weather system. These results indicate that temperature played the most crucial role in the haze event in NCP, as well as in the O 3 change in SC. This valuable information will ultimately contribute to our ability to predict air pollution under future emission scenarios and changing weather patterns that may be influenced by climate change. [ABSTRACT FROM AUTHOR]

Solar radiation modification by a sustained deliberate source of SO2 into the stratosphere (strat-SRM) has been proposed as an option for climate intervention. Global interactive aerosol–chemistry–climate models are often used to investigate the potential cooling efficiencies and associated side effects of hypothesized strat-SRM scenarios. A recent model intercomparison study for composition–climate models with interactive stratospheric aerosol suggests that the modeled climate response to a particular assumed injection strategy depends on the type of aerosol microphysical scheme used (e.g., modal or sectional representation) alongside host model resolution and transport. Compared to short-duration volcanic SO2 emissions, the continuous SO2 injections in strat-SRM scenarios may pose a greater challenge to the numerical implementation of microphysical processes such as nucleation, condensation, and coagulation. This study explores how changing the time steps and sequencing of microphysical processes in the sectional aerosol–chemistry–climate model SOCOL-AERv2 (40 mass bins) affects model-predicted climate and ozone layer impacts considering strat-SRM by SO2 injections of 5 and 25 Tg(S) yr −1 at 20 km altitude between 30° S and 30° N. The model experiments consider the year 2040 to be the boundary conditions for ozone-depleting substances and greenhouse gases (GHGs). We focus on the length of the microphysical time step and the call sequence of nucleation and condensation, the two competing sink processes for gaseous H2SO4. Under stratospheric background conditions, we find no effect of the microphysical setup on the simulated aerosol properties. However, at the high sulfur loadings reached in the scenarios injecting 25 Tg(S) yr −1 of SO2 with a default microphysical time step of 6 min, changing the call sequence from the default "condensation first" to "nucleation first" leads to a massive increase in the number densities of particles in the nucleation mode (R<0.01 µm) and a small decrease in coarse-mode particles (R>1 µm). As expected, the influence of the call sequence becomes negligible when the microphysical time step is reduced to a few seconds, with the model solutions converging to a size distribution with a pronounced nucleation mode. While the main features and spatial patterns of climate forcing by SO 2 injections are not strongly affected by the microphysical configuration, the absolute numbers vary considerably. For the extreme injection with 25 Tg(S) yr −1 , the simulated net global radiative forcing ranges from - 2.3 to - 5.3 Wm-2 , depending on the microphysical configuration. Nucleation first shifts the size distribution towards radii better suited for solar scattering (0.3 µm

Understanding how different physical and chemical atmospheric processes affect the formation of fine particles has been a persistent challenge. Inferring causal relations between the various measured features affecting the formation of secondary organic aerosol (SOA) particles is complicated since correlations between variables do not necessarily imply causality. Here, we apply a state-of-the-art information transfer measure coupled with the Koopman operator framework to infer causal relations between isoprene epoxydiol SOA (IEPOX-SOA) and different chemistry and meteorological variables derived from detailed regional model predictions over the Amazon rainforest. IEPOX-SOA represents one of the most complex SOA formation pathways and is formed by the interactions between natural biogenic isoprene emissions and anthropogenic emissions affecting sulfate, acidity and particle water. Since the regional model captures the known relations of IEPOX-SOA with different chemistry and meteorological features, their simulated time series implicitly include their causal relations. We show that our causal model successfully infers the known major causal relations between total particle phase 2-methyl tetrols (the dominant component of IEPOX-SOA over the Amazon) and input features. We provide the first proof of concept that the application of our causal model better identifies causal relations compared to correlation and random forest analyses performed over the same dataset. Our work has tremendous implications, as our methodology of causal discovery could be used to identify unknown processes and features affecting fine particles and atmospheric chemistry in the Earth's atmosphere. [ABSTRACT FROM AUTHOR]

Formic and acetic acids are major organic species in cloud water and affect precipitation acidity. In atmospheric models, their losses are limited to chemical oxidation in the gas and aqueous phases and deposition processes. Previous lab studies suggest that these acids can be efficiently biodegraded in water by atmospherically relevant bacteria. However, the importance of biodegradation as a loss process in the atmospheric multiphase system has not been fully assessed. We implemented biodegradation as a sink of formic and acetic acids in a detailed atmospheric multiphase chemistry model. In our model, biodegradation is considered in 0.1 % of cloud droplets according to atmospheric bacteria concentrations of 0.1 cm -3. We predict that up to 20 ppt h -1 formic acid and 5 ppt h -1 acetic acid are biodegraded. This translates into a concentration change of 20 % and 3 % in addition to that caused by chemical losses. Our sensitivity studies suggest that acetic acid is most efficiently biodegraded at pH > 5, whereas biodegradation is least efficient for formic acid under such conditions. This trend can be explained by the fact that formic acid partitions more efficiently into the aqueous phase due to its higher Henry's law constant (KH,eff(HCOOH)=2×105 M atm -1 vs. KH,eff(CH3COOH)=3×104 M atm -1 at pH = 5). Therefore, under such conditions, formic acid evaporates less efficiently from bacteria-free droplets, resulting in less formic acid in the gas phase for dissolution bacteria-containing droplets to replenish biodegraded acid. Our analysis demonstrates that previous estimates of the importance of atmospheric biodegradation were often biased high as they did not correctly account for such uptake limitation in bacteria-containing droplets. The results suggest that, under specific conditions, biological processes can significantly affect atmospheric composition and concentrations in particular volatile, moderately soluble organics. [ABSTRACT FROM AUTHOR]

Fixed nitrogen species generated by the early Earth's atmosphere are thought to be critical to the emergence of life and the sustenance of early metabolisms. A previous study estimated nitrogen fixation in the Hadean Earth's N2/CO2-dominated atmosphere; however, that previous study only considered a limited chemical network that produces NOx species (i.e., no HCN formation) via the thermochemical dissociation of N2 and CO2 in lightning flashes, followed by photochemistry. Here, we present an updated model of nitrogen fixation on Hadean Earth. We use the Chemical Equilibrium with Applications (CEA) thermochemical model to estimate lightning-induced NO and HCN formation and an updated version of KINETICS, the 1-D Caltech/JPL photochemical model, to assess the photochemical production of fixed nitrogen species that rain out into the Earth's early ocean. Our updated photochemical model contains hydrocarbon and nitrile chemistry, and we use a Geant4 simulation platform to consider nitrogen fixation stimulated by solar energetic particle deposition throughout the atmosphere. We study the impact of a novel reaction pathway for generating HCN via HCN2, inspired by the experimental results which suggest that reactions with CH radicals (from CH4 photolysis) may facilitate the incorporation of N into the molecular structure of aerosols. When the HCN2 reactions are added, we find that the HCN rainout rate rises by a factor of five in our 1-bar case and is about the same in our 2- and 12-bar cases. Finally, we estimate the equilibrium concentration of fixed nitrogen species under a kinetic steady state in the Hadean ocean, considering loss by hydrothermal vent circulation, photoreduction, and hydrolysis. These results inform our understanding of environments that may have been relevant to the formation of life on Earth, as well as processes that could lead to the emergence of life elsewhere in the universe. [ABSTRACT FROM AUTHOR]

The tentative detection of ppb levels of phosphine (PH[sub 3]) in the clouds of Venus was extremely surprising, as this reduced gas was not expected to be a component of Venus' oxidized atmosphere. Despite potential confirmation in legacy Pioneer Venus mass spectrometry data, the detection remains controversial. Here we review the potential production of phosphine by gas reactions, surface and sub-surface geochemistry, photochemistry, and other nonequilibrium processes. None of these potential phosphine production pathways is sufficient to explain the presence of phosphine in Venus atmosphere at near the observed abundance. The source of atmospheric PH[sub 3] could be unknown geo- or photochemistry, which would imply that the consensus on Venus' chemistry is significantly incomplete. An even more extreme possibility is that a strictly aerial microbial biosphere produces PH[sub 3]. The detection of phosphine adds to the complexity of chemical processes in the Venusian environment and motivates better quantitation of the gas phase chemistry of phosphorus species and in situ follow-up sampling missions to Venus. [ABSTRACT FROM AUTHOR]

The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) is currently providing the only measurements of vertically resolved chlorodifluoromethane (HCFC-22) from space. This study assesses the ACE-FTS HCFC-22 v5.2 product in the upper troposphere and lower stratosphere, as well as simulations of HCFC-22 from a 39-year specified dynamics run of the Canadian Middle Atmosphere Model (CMAM39) in the same region. In general, ACE-FTS HCFC-22 observations tend to agree with subsampled CMAM39 data to within ±5 %, except for between ∼ 15 and 25 km in the extratropical regions where ACE-FTS exhibits a negative bias of 5 %–30 % and near 6 km in the tropics where ACE-FTS exhibits a bias of - 15 %. When comparing against correlative satellite, aircraft, and balloon data, ACE-FTS typically exhibits a low bias on the order of 0 %–10 % between ∼ 5 and 15 km and is within ±15 % between ∼ 15 and 25 km. ACE-FTS, CMAM39, and surface flask measurements from the NOAA Global Monitoring Laboratory's surface air-sampling network all exhibit consistent tropospheric HCFC-22 trends ranging between 6.8 and 7.8 ppt yr -1 (within 95 % confidence) for 2004–2012 and between 3.1 and 4.7 ppt yr -1 (within 95 % confidence) for 2012–2018. Interhemispheric differences (IHDs) of HCFC-22 were also derived using ACE-FTS, NOAA, and CMAM39 data, and all three yielded consistent and correlated (r≥0.42) IHD time series, with the results indicating that surface IHD values decreased at a rate of 2.2 ± 1.1 ppt per decade between 2004 and 2018. [ABSTRACT FROM AUTHOR]

Isoprene, a key biogenic volatile organic compound, plays a pivotal role in atmospheric chemistry. Due to its high reactivity, this compound contributes significantly to the production of tropospheric ozone in polluted areas and to the formation of secondary organic aerosols. The assessment of biogenic emissions is of great importance for regional and global air quality evaluation. In this study, we implemented the biogenic emission model MEGANv2.1 (Model of Emissions of Gases and Aerosols from Nature, version 2.1) in the surface model SURFEXv8.1 (SURface EXternalisée in French, version 8.1). This coupling aims to improve the estimation of biogenic emissions using the detailed vegetation-type-dependent treatment included in the SURFEX vegetation ISBA (Interaction between Soil Biosphere and Atmosphere) scheme. This scheme provides vegetation-dependent parameters such as leaf area index and soil moisture to MEGAN. This approach enables a more accurate estimation of biogenic fluxes compared to the stand-alone MEGAN model, which relies on average input values for all vegetation types. The present study focuses on the assessment of the SURFEX–MEGAN model isoprene emissions. An evaluation of the coupled SURFEX–MEGAN model results was carried out by conducting a global isoprene emission simulation in 2019 and by comparing the simulation results with other MEGAN-based isoprene inventories. The coupled model estimates a total global isoprene emission of 443 Tg in 2019. The estimated isoprene is within the range of results obtained with other MEGAN-based isoprene inventories, ranging from 311 to 637 Tg. The spatial distribution of SURFEX–MEGAN isoprene is consistent with other studies, with some differences located in low-isoprene-emission regions. Several sensitivity tests were conducted to quantify the impact of different model inputs and configurations on isoprene emissions. Using different meteorological forcings resulted in a ± 5 % change in isoprene emissions using MERRA (Modern-Era Retrospective analysis for Research and Applications) and IFS (Integrated Forecasting System) compared with ERA5. The impact of using different emission factor data was also investigated. The use of PFT (plant functional type) spatial coverage and PFT-dependent emission potential data resulted in a 12 % reduction compared to using the isoprene emission potential gridded map. A significant reduction of around 38 % in global isoprene emissions was observed in the third sensitivity analysis, which applied a parameterization of soil moisture deficit, particularly in certain regions of Australia, Africa, and South America. The significance of coupling the SURFEX and MEGAN models lies particularly in the ability of the coupled model to be forced with meteorological data from any period. This means, for instance, that this system can be used to predict biogenic emissions in the future. This aspect of our work is significant given the changes that biogenic organic compounds are expected to undergo as a result of changes in their climatic factors. [ABSTRACT FROM AUTHOR]

The interactions between the terrestrial biosphere, atmospheric chemistry, and climate involve complex feedbacks that have traditionally been modeled separately. We present a new framework that couples the Yale Interactive terrestrial Biosphere (YIBs) model, a dynamic plant-chemistry model, with the RegCM-Chem model. RegCM-Chem–YIBs integrates meteorological variables and atmospheric chemical composition from RegCM-Chem with land surface parameters from YIBs. The terrestrial carbon flux calculated by YIBs is fed back into RegCM-Chem interactively, thereby representing the interactions between fine particulate matter (PM 2.5), ozone (O 3), and carbon dioxide (CO 2). For testing purposes, we carry out a 1-year simulation (2016) at a 30 km horizontal resolution over East Asia with RegCM-Chem–YIBs. The model accurately captures the spatio-temporal distribution of climate, chemical composition, and ecological parameters. In particular, the estimated O 3 and PM 2.5 are consistent with ground observations, with correlation coefficients (R) of 0.74 and 0.65, respectively. The simulated CO 2 concentration is consistent with observations from six sites (R ranged from 0.89 to 0.97) and exhibits a similar spatial pattern when compared with carbon assimilation products. RegCM-Chem–YIBs produces reasonably good gross primary productivity (GPP) and net primary productivity (NPP), showing seasonal and spatial distributions consistent with satellite observations, and mean biases (MBs) of 0.13 and 0.05 kg C m -2 yr -1. This study illustrates that RegCM-Chem–YIBs is a valuable tool to investigate coupled interactions between the terrestrial carbon cycle, atmospheric chemistry, and climate change at a higher resolution on a regional scale. [ABSTRACT FROM AUTHOR]

The transport history of tropospheric air masses above the tropical western Pacific (TWP) is reflected by the local ozone and relative humidity (RH) characteristics. In boreal winter, the TWP is the main global entry point for air masses into the stratosphere and therefore a key region of atmospheric chemistry and dynamics. Our study aims to identify air masses with different pathways to the TWP using ozone and radio soundings from Palau from 2016–2019. Supported by backward trajectory calculations, we found five different types of air masses. We further defined locally controlled ozone and RH background profiles based on monthly statistics and analyzed corresponding anomalies in the 5–10 km altitude range. Our results show a bimodality in RH anomalies. Humid and ozone-poor background air masses are of local or Pacific convective origin and occur year-round, but they dominate from August until October. Anomalously dry and ozone-rich air masses indicate a non-local origin in tropical Asia and are transported to the TWP via an anticyclonic route, mostly from February to April. The geographic location of origin suggests anthropogenic pollution or biomass burning as a cause for ozone production. We propose large-scale descent within the tropical troposphere and radiative cooling in connection with the Hadley circulation as being responsible for the dehydration during transport. The trajectory analysis revealed no indication of a stratospheric influence. Our study thus presents a valuable contribution to the discussion about anomalous layers of dry ozone-rich air observed in ozone-poor background profiles in the TWP. [ABSTRACT FROM AUTHOR]

A new upper stratospheric (35–60 km) temperature data product has been produced using Optical Spectrograph and InfraRed Imager System (OSIRIS) limb-scattered spectra that now spans over 22 years. Temperature is calculated by first estimating the Rayleigh scattering signal and then integrating hydrostatic balance combined with the ideal gas law. Uncertainties are estimated to be 1–5 K, with a vertical resolution of 3–4 km. Correlative comparisons with the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) and the Microwave Limb Sounder on Aura (MLS) are consistent with these uncertainty estimates and generally have no regions of statistically significant drift. The data product has been publicly released as part of the nominal OSIRIS v7.3 processing. [ABSTRACT FROM AUTHOR]

Aqueous-phase chemical processes in clouds, fog, and deliquescent aerosols are known to alter atmospheric composition and acidity significantly. Traditionally, global and regional models predict aerosol composition by relying on thermodynamic equilibrium models and neglect non-equilibrium processes. Here, we present the AERosol CHEMistry (GMXe–AERCHEM, v1.0) sub-submodel developed for the Modular Earth Submodel System (MESSy) as an add-on to the thermodynamic equilibrium model (i.e. ISORROPIA-II) used by MESSy's Global Modal-aerosol eXtension (GMXe) submodel. AERCHEM allows the representation of non-equilibrium aqueous-phase chemistry of varying complexity in deliquescent fine aerosols. We perform a global simulation for the year 2010 by using the available detailed kinetic model for the chemistry of inorganic and small oxygenated organics. We evaluate AERCHEM's performance by comparing the simulated concentrations of sulfate, nitrate, ammonium, and chloride to in situ measurements of three monitoring networks. Overall, AERCHEM reproduces observed concentrations reasonably well. We find that, especially in the USA, the consideration of non-equilibrium chemistry in deliquescent aerosols reduces the model bias for sulfate, nitrate, and ammonium when compared to simulated concentrations by ISORROPIA-II. Over most continental regions, fine-aerosol acidity simulated by AERCHEM is similar to the predictions by ISORROPIA-II, but simulated aerosol acidity tends to be slightly lower in most regions. The consideration of non-equilibrium chemistry in deliquescent aerosols leads to a significantly higher aerosol acidity in the marine boundary layer, which is in line with observations and recent literature. AERCHEM allows an investigation of the global-scale impact of aerosol non-equilibrium chemistry on atmospheric composition. This will aid in the exploration of key multiphase processes and improve the model predictions for oxidation capacity and aerosols in the troposphere. [ABSTRACT FROM AUTHOR]

Atmospheric methane is one of the major greenhouse gases and has a great impact on climate change. To obtain the polluted levels of atmospheric methane in the ground-level range, this study used satellite observations and vertical profile features derived by atmospheric chemistry model to estimate the ground methane concentrations in first. Then, the improved daily ground-level atmospheric methane concentration dataset with full spatial coverage (100%) and 5-km resolution in mainland China from 2019 to 2021 were retrieved by station-based observations and gaussian regression model. The overall estimated deviation between the estimated ground methane concentrations and the WDCGG station-based measurements is less than 10 ppbv. The R by tenfold cross-validation is 0.93, and the R2 is 0.87. The distribution of the ground-level methane concentrations in the Chinese region is characterized by high in the east and south, and low in the west and north. On the time scale, ground-level methane concentration in the Chinese region is higher in winter and lower in summer. Meanwhile, the spatial and temporal distribution and changes of ground-level methane in local areas have been analyzed using Shandong Province as an example. The results have a potential to detect changes in the distribution of methane concentration. [ABSTRACT FROM AUTHOR]

There is considerable academic interest in the potential for air quality improvement as a co-benefit of climate change mitigation. Few studies use regional air quality models for simulating future co-benefits, but many use global chemistry-climate model output. Using regional atmospheric chemistry could provide a better representation of air quality changes than global chemistry-climate models, especially by improving the representation of elevated urban concentrations. We use a detailed regional atmospheric chemistry model (WRF-Chem v 4.2) to model European air quality in 2050 compared to 2014 following three climate change mitigation scenarios. We represent different climate futures by using air pollutant emissions and chemical boundary conditions (from CESM2-WACCM output) for three Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0; a high, medium and low mitigation pathway). We find that in 2050, following SSP1-2.6, mean population-weighted PM2.5 concentrations across European countries reduces by 52 % compared to 2014. Whilst under SSP2-4.5, this average reduction is 34 %. The smallest average reduction was 18 % by following SSP3-7.0. Maximum 6-monthly-mean daily-maximum 8 h (6mDM8h) ozone (O3) is reduced across Europe by 15 % following SSP1-2.6, and 3 % following SSP2-4.5, but increases by 13 % following SSP3-7.0. This demonstrates clear co-benefits of climate mitigation. The additional resolution allows us to analyse regional differences and identify key sectors. We find that mitigation of agricultural emissions will be key for attaining meaningful co-benefits of mitigation policies, evidenced by the importance of changes in NO3 aerosol mass to determining future PM2.5 air quality and changes in CH4 emissions to future O3 air quality. [ABSTRACT FROM AUTHOR]

Mesospheric electrical discharges, known as sprites and formed by fast-propagating streamers, have been shown to create localized enhancements of atmospheric constituents such as N, O, NO x , N 2 O, and HO x , as indicated by both modelling results and space-based measurements. In this study, we incorporate the occurrence rate of sprites into a chemistry–climate model using meteorological parameters as a proxy. Additionally, we introduce the injection of chemical species by sprites into the model based on electrodynamical modelling of individual sprite streamers and observations from space. Our modelling results show a good agreement between the simulated sprite distribution and observed data on a global scale. While the global influence of sprites on the atmospheric chemistry is found to be negligible, our findings reveal their measurable chemical influence at the regional scale, particularly for the concentration of HNO 3 and HNO 4 within the mesosphere. The simulations also suggest that sprites could be responsible for the observed NO 2 anomalies at an altitude of 52 km above thunderstorms, as reported by MIPAS. Finally, a projected simulation reveals that the occurrence rate of sprites could increase at a rate of 14 % per 1 K rise in the global temperature. [ABSTRACT FROM AUTHOR]