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Dry conditions associated with the El Niño–Southern Oscillation (ENSO) and a positive Indian Ocean Dipole (IOD) are known to have caused major fire pollution events and intense carbon emissions over a vast spatial expanse of Indonesia in October 2006 and 2015. During these two events, a substantial increase in the carbon monoxide (CO) mixing ratio was detected by in situ measurements at Lulin Atmospheric Background Station (LABS; 23.47∘ N 120.87∘ E; 2862 ma.s.l.) in Taiwan, which is the only background station in the subtropical western North Pacific region. Compared to the long-term October mean (2006–2021), CO was elevated by ∼ 47.2 ppb (parts per billion; 37.2 %) and ∼ 36.7 ppb (28.9 %) in October 2006 and 2015, respectively. This study delineates plausible pathways for the CO transport from Indonesia to LABS using Measurement of Pollution in the Troposphere (MOPITT) CO observations and Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalysis products (winds and geopotential height – GpH). Two simultaneously occurring transport pathways were identified, namely (i) horizontal transport in the free troposphere and (ii) vertical transport through the Hadley circulation (HC). The GpH analysis of both events revealed the presence of a high-pressure anticyclone over the northern part of the South China Sea (SCS), which played an important role in the free-tropospheric horizontal transport of CO. In this scenario, CO in the free troposphere is transported on the western edge of the high-pressure system and then driven by subtropical westerlies to LABS. Simultaneously, uplifted CO over Indonesia can enter the HC and be transferred to subtropical locations such as LABS. The vertical cross section of the MOPITT CO and MERRA-2 vertical pressure velocity supported the transport of CO through the HC. Furthermore, the results revealed a distinct HC strength in two events (higher in 2006 compared to 2015) due to the different ENSO conditions. Overall, the present findings can provide some insights into understanding the regional transport of pollution over Southeast Asia and the role of climate conditions on transport pathways.

Photochemical ozone pollution is a serious air quality problem under weak synoptic conditions in many areas worldwide. Volatile organic compounds (VOCs) are largely responsible for ozone production in urban areas where NOx mixing ratios are high while usually not a limiting precursor to ozone. In this study, the Community Multiscale Air Quality model – Higher-order Direct Decoupled Method (CMAQ-HDDM) at an urban-scale resolution (1.0 km x 1.0 km) in conjunction with positive matrix factorization (PMF) was used to identify the dominant sources of highly sensitive VOC species to ozone formation in southern Taiwan, a complex region of coastal urban and industrial parks and inland mountainous areas. First-order, second-order and cross sensitivities of ozone concentrations to domain-wide (i.e. urban, suburban and rural) NOx and VOC emissions were determined for the study area. Negative (positive) first-order sensitivities to NOx emissions are dominant over urban (inland) areas, confirming ozone production sensitivity favors the VOC-limited regime (NOx-limited regime) in southern Taiwan. Furthermore, most of the urban areas also exhibited negative second-order sensitivity to NOx emissions, indicating a negative O3 convex response where the linear increase of O3 from decreasing NOx emissions was largely attenuated by the non-linear effects. Due to the solidly VOC-limited regime and the relative insensitivity of O3 production to increases or decreases of NOx emissions, this study pursued the VOC species that contributed the most to ozone formation. PMF analysis driven by VOCs resolved 8 factors including mixed industry (21 %), vehicle emissions (22 %), solvent usage (17 %), biogenic (12 %), plastic industry (10 %), aged air mass (7 %), motorcycle exhausts (7 %), and manufacturing industry (5 %). Furthermore, a composite index that quantitatively combined the CMAQ-HDDM sensitivity coefficient and PMF resolved factor contribution, was developed to identify the key VOC species that should be targeted for effective ozone abatement. Our results indicate that VOC control measures should target on (1) solvent usage for painting, coating and the printing industry, which emits abundant toluene and xylene, (2) gasoline fuel vehicle emissions of n-butane, isopentane, isobutane and n-pentane, and (3) ethylene and propylene emissions from the petrochemical industry.

Dry conditions associated with El Niño and a positive Indian Ocean Dipole (IOD) are known to have caused major fire pollution events and intense carbon emissions over a vast spatial expanse of Indonesia in October 2006 and 2015. During these two events, a substantial increase in carbon monoxide (CO) mixing ratio was detected by in-situ measurements at Lulin Atmospheric Background Station (LABS, 23.47° N 120.87° E, 2,862 m ASL) in Taiwan, the only background station in the subtropical western North Pacific region. Compared to the long-term October mean (2006–2021), CO was elevated by ~47.2 ppb (37.2 %) and ∼36.7 ppb (28.9 %) in October 2006 and 2015, respectively. In this study, plausible pathways for CO transport from Indonesia to LABS are delineated by using MOPITT CO observations and MERRA-2 reanalysis products (winds and geopotential height (GpH)). Two simultaneously occurring transport pathways were identified: (i) horizontal transport in the free troposphere and (ii) vertical transport through the Hadley circulation (HC). The GpH analysis of both events revealed the presence of a high-pressure anticyclone over the northern part of the South China Sea (SCS), which played an important role in the free tropospheric horizontal transport of CO. In this scenario, CO in the free troposphere is transported on the western edge of the high-pressure system and then driven by subtropical westerlies to LABS. Simultaneously, uplifted CO over Indonesia can enter the HC and transfer to subtropical locations such as LABS. The vertical cross-section of MOPITT CO and MERRA-2 vertical pressure velocity supported the transport of CO through the HC. Further, the results revealed a distinct HC strength in two events (higher in 2006 compared to 2015) due to the different El Niño conditions. Overall, the present findings can provide some insights into understanding the regional transport of pollution over Southeast Asia and the role of climate conditions on transport pathways.

INTRODUCTION Coronavirus disease 2019 (COVID-19) emerged in Wuhan, China in late 2019, and soon unfolded as a global outbreak accompanied by declarations of a public health emergency of international concern (PHEIC) and later a pandemic from the World Health Organization (WHO). COVID-19 has resulted in 2,626,321 confirmed cases and 181,938 reported deaths worldwide (as of 14 April 2020). The underlying virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a highly contagious novel coronavirus that transmits as an aerosol and threatens people of all ages, from infant to geriatric, while those with cardiovascular disease are recognized as particularly susceptible to more severe symptoms from SARS-CoV-2 infection. WHO recommends using a mask to limit the COVID-19 outbreak; however, SARS-CoV-2 transmission models and its removal efficiency by wearing a mask remain unclear. Furthermore, differences in the field-specific definitions/terminologies related to transmission and mask usage tend to cause confusion and misunderstanding among both experts and the public.

Semi-volatile and intermediate-volatility organic compounds (SVOCs and IVOCs) from anthropogenic sources are likely to be important precursors of secondary organic aerosol (SOA) in urban airsheds, yet their treatment in most models is based on limited and obsolete data or completely missing. Additionally, gas-phase oxidation of organic precursors to form SOA is influenced by the presence of nitric oxide (NO), but this influence is poorly constrained in chemical transport models. In this work, we updated the organic aerosol model in the UCD/CIT (University of California at Davis/California Institute of Technology) chemical transport model to include (i) a semi-volatile and reactive treatment of primary organic aerosol (POA), (ii) emissions and SOA formation from IVOCs, (iii) the NOx influence on SOA formation, and (iv) SOA parameterizations for SVOCs and IVOCs that are corrected for vapor wall loss artifacts during chamber experiments. All updates were implemented in the statistical oxidation model (SOM) that simulates the oxidation chemistry, thermodynamics, and gas–particle partitioning of organic aerosol (OA). Model treatment of POA, SVOCs, and IVOCs was based on an interpretation of a comprehensive set of source measurements available up to the year 2016 and resolved broadly by source type. The NOx influence on SOA formation was calculated offline based on measured and modeled VOC:NOx ratios. Finally, the SOA formation from all organic precursors (including SVOCs and IVOCs) was modeled based on recently derived parameterizations that accounted for vapor wall loss artifacts in chamber experiments. The updated model was used to simulate a 2-week summer episode over southern California at a model resolution of 8 km. When combustion-related POA was treated as semi-volatile, modeled POA mass concentrations were reduced by 15 %–40 % in the urban areas in southern California but were still too high when compared against “hydrocarbon-like organic aerosol” factor measurements made at Riverside, CA, during the Study of Organic Aerosols at Riverside (SOAR-1) campaign of 2005. Treating all POA (except that from marine sources) to be semi-volatile, similar to diesel exhaust POA, resulted in a larger reduction in POA mass concentrations and allowed for a better model–measurement comparison at Riverside, but this scenario is unlikely to be realistic since this assumes that POA from sources such as road and construction dust are semi-volatile too. Model predictions suggested that both SVOCs (evaporated POA vapors) and IVOCs did not contribute as much as other anthropogenic precursors (e.g., alkanes, aromatics) to SOA mass concentrations in the urban areas (NOx-dependent. Accounting for the influence of NOx using the VOC:NOx ratios resulted in better predictions of OA mass concentrations in rural/remote environments but still underpredicted OA mass concentrations in urban environments. The updated model's performance against measurements combined with the results from the sensitivity simulations suggests that the OA mass concentrations in southern California are constrained within a factor of 2. Finally, simulations performed for the year 2035 showed that, despite reductions in VOC and NOx emissions in the future, SOA mass concentrations may be higher than in the year 2005, primarily from increased hydroxyl radical (OH) concentrations due to lower ambient NO2 concentrations.

This study aimed to develop a technique to chemically characterize odor issues in neighborhoods of designated industrial zones with pronounced emissions of volatile organic compounds (VOCs). Due to the elusive nature of odor plumes, speedy detection with sufficient sensitivity is required to capture the plumes. In this demonstration, proton-transfer-reaction mass spectrometry (PTR-MS) was used as the front-line detection tool in an industrial zone to guide sampling canisters for in-laboratory analysis of 106 VOCs by gas chromatography-mass spectrometry/flame ionization detector (GC-MS/FID). The fast but less accurate PTR-MS coupled with the slow but accurate GC-MS/FID method effectively eliminates the drawbacks of each instrument and fortifies the strength of both when combined. A 10-day PTR-MS field screening period was conducted to determine suitable trigger VOC species with exceedingly high mixing ratios that were likely the culprits of foul odors. Twenty canister samples were then collected, triggered by m/z 43, 61 (ethyl acetate, fragments, EA), m/z 73 (methyl ethyl ketone, MEK), or m/z 88 (morpholine) in all cases. Internal consistency was confirmed by the high correlation of critical species in the PTR-MS and trigger samples. Several long-lived halocarbons were exploited as the intrinsic internal reference for quality assurance. Oxygenated VOCs (OVOCs) accounted for 15%-75% of the total VOC mixing ratios in the triggered samples. However, EA and MEK, the most prominent OVOC species, did not appear to have common sources with morpholine, which presented with PTR-MS peaks incoherent with the other OVOCs. Nevertheless, these distinctive OVOC plumes were consistent with the multiple types of odor reported by the local residents. In contrast with the triggered sampling, random samples in the same industrial zone and roadside samples in a major metropolitan area were collected. The pronounced OVOC content in the triggered samples highlighted the advantage over random grab sampling to address odor issues.

Aerosol type plays a critical role in the relationship between aerosol optical depth (AOD) and particulate matter (PM) mass concentration. Here, we present a mathematical formulation of how PM...

Traffic-related air pollutants (TRAPs) pose a serious health hazard for residents and commuters in urban areas. In this study, a real-time mobile monitoring system was deployed in Taipei, a typical East Asian city with an overlap of high population density, traffic, and special structures (e.g., viaducts), to capture the on-road TRAPs at different times of the day. In general, black carbon, ultrafine particles (UFPs), CO concentrations, and lung deposition surface area (LDSA) were positively correlated with traffic flow, and for PM2.5, a more independent fluctuating concentration was observed. During rush-hour periods, the mean concentrations of UFPs, PM2.5, and LDSA were 6.12 × 104 ± 3.83 × 104 cm−3, 23 ± 8 μg/m3, and 2.29 × 102 ± 1.20 × 102 μm2/cm3, respectively. Additionally, the UFP number concentration and LDSA were two times higher along the high-traffic commuting route than along the lower traffic route. Pollutants tended to accumulate at sites near viaducts and high buildings and were significantly influenced by vehicle composition. In this study, the ratio of LDSA to total particle surface area concentration was used as an indicator of the degree of particle irregularity, which was directly related to aging during transport.

International audience; Nitrous acid (HONO) is an important radical precursor that can impact secondary pollutant levels, especially in urban environments. Due to uncertainties in its heterogeneous formation mechanisms, models often under predict HONO concentrations. A number of heterogeneous sources at the ground have been proposed but there is no consensus about which play a significant role in the urban boundary layer. We present a new one-dimensional chemistry and transport model which performs surface chemistry based on molecular collisions and chemical conversion, allowing us to add detailed HONO formation chemistry at the ground. We conducted model runs for the 2010 CalNex campaign, finding good agreement with observations for key species such as O3, NOx, and HOx. With the ground sources implemented, the model captures the diurnal and vertical profile of the HONO observations. Primary HOx production from HONO photolysis is 2–3 times more important than O3 or HCHO photolysis at mid-day, below 10 m. The HONO concentration, and its contribution to HOx, decreases quickly with altitude. Heterogeneous chemistry at the ground provided a HONO source of 2.5 × 1011 molecules cm−2 s−1 during the day and 5 × 1010 molecules cm−2 s−1 at night. The night time source was dominated by NO2 hydrolysis. During the day, photolysis of surface HNO3/nitrate contributed 45%–60% and photo-enhanced conversion of NO2 contributed 20%–45%. Sensitivity studies addressing the uncertainties in both photolytic mechanisms show that, while the relative contribution of either source can vary, HNO3/nitrate is required to produce a surface HONO source that is strong enough to explain observations.

Light-absorbing organic carbon (or brown carbon, BrC) has been recognized as a critical driver in regional-to-global climate change on account of its significant contribution to light absorption. BrC sources vary from primary combustion processes (burning of biomass, biofuel, and fossil fuel) to secondary formation in the atmosphere. This paper investigated the light-absorbing properties of BrC such as site-specific mass absorption cross-section (MACBrC), absorption Angstrom exponent (AAEBrC), and the absorbing component of the refractive index (kBrC) by using light absorption measurements from a 7-wavelength aethalometer over an urban environment of Chiang Mai, Thailand in northern peninsular Southeast Asia (PSEA), from March to April 2016. The contribution of BrC to total aerosol absorption (mean ± SD) was 46 ± 9%, 29 ± 7%, 24 ± 6%, 20 ± 4%, and 15 ± 3% at 370, 470, 520, 590, and 660 nm, respectively, highlighting the significant influence of BrC absorption on the radiative imbalance over northern PSEA. Strong and significant associations between BrC light absorption and biomass-burning (BB) organic tracers highlighted the influence of primary BB emissions. The median MACBrC and kBrC values at 370 nm were 2.4 m2 g−1 and 0.12, respectively. The fractional contribution of solar radiation absorbed by BrC relative to BC (mean ± SD) in the 370–950 nm range was estimated to be 34 ± 7%, which can significantly influence the regional radiation budget and consequently atmospheric photochemistry. This study provides valuable information to understand BrC absorption over northern PSEA and can be used in model simulations to reassess the regional climatic impact with greater accuracy.

Many aromatic compounds (e.g., polycyclic aromatic hydrocarbons (PAHs)) found in atmospheric aerosols are toxic and exist in both unsubstituted and substituted forms. Previous studies have mainly concentrated on investigating unsubstituted PAHs, leaving the substituted compounds largely uncharacterized. This study focuses on detection of both unsubstituted and substituted aromatics in ambient aerosol samples using ultrahigh-resolution mass spectrometry. Aerosol samples collected from roadside, urban, and suburban sites in Hong Kong were characterized by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) coupled with atmospheric pressure photoionization (APPI) or electrospray ionization (ESI). In the APPI+ mode, 166 aromatic CH formulas (i.e., formulas containing C and H only and with a double bond equivalent (DBE) of 4 or higher) were determined through molecular formula calculations based on an accurate m/z determination. Among the determined aromatic CH formulas, 141 are possible alkylated monocyclic aromatic hydrocarbon (MAH) or PAH formulas, and account for ≥ 45% of the total intensity by aromatic CH+ formulas. Both APPI+ and ESI+ are effective in detecting nitroaromatics (i.e., CHO2N1 formulas and DBE ≥ 5). The two ionization modes provide complementary formula coverage, with formulas determined by APPI+ extending to higher DBE and those by ESI+ covering higher carbon numbers. Alkylated nitrobenzene compounds are the most abundant among nitroaromatics, and they, together with alkylated nitro-PAHs, account for > 80% of the total intensity of aromatic CHO2N+ formulas, indicating the importance of these compounds in real aerosol samples. Aromatic CHN+ and CHO+ formulas are also determined, confirming the atmospheric presence of some previously reported O- and N-containing aromatic compounds and revealing new possible formulas. The determination of aromatic organic formulas in this study provides useful guidance for future quantitative analysis of hazardous aromatic compounds. Future work is needed to determine the abundance and to study the toxicity of alkylated MAHs and PAHs outside the 16 US EPA priority PAH compounds.

Volcanic eruptions are important natural sources of gases and aerosols to the environment. However, their impact on the global cycle of trace elements, including mercury (Hg), remains poorly understood. On 9 April 2021, La Soufriere volcano (13.33°N, 61.18°W) erupted in the Caribbean Sea. Ozone Monitoring Instrument (OMI) measurements of sulfur dioxide (SO2) tracked the transport of volcanic SO2 in the troposphere over long distances from the source, including to the western North Pacific ∼10 day after eruption. A spike in gaseous and particle-bound mercury concentrations along with a peak in aerosol back-scattering coefficient at Lulin Atmospheric Background Station (LABS, 23.47°N, 120.87°E; 2862 m AMSL) coincided with the volcanic plume transport on 19 April. The slope of gaseous elemental mercury vs. carbon monoxide concentrations during the event was 0.027, which is distinctly higher than for Southeast Asia biomass burning (slope = 0.005) and East Asia outflow (0.011) pollution sources. Arrival of the plume high above Taiwan was confirmed by significant changes in signature aerosol properties. Thus, with critical observational evidence, our study reported for the first time enhanced mercury levels ∼18000 km downwind from a volcano source, providing an important check on volcanic Hg emission strength.

In this study, we investigated the influences of stratospheric intrusion (SI) on the tropospheric ozone (O3) at Lulin Atmospheric Background Station (LABS, 2862 m MSL), a representative high-altitude site in East Asia. Thresholds for surface O3, carbon monoxide (CO), and relative humidity (RH) were set to identify SI events at LABS. Accordingly, 3.0% of the observation period was impacted by SI leading to a net O3 enhancement of 14.6 ± 9.6 ppb at LABS. Factors influencing the two most common SI event types affecting LABS, i.e. tropopause folds (major) and tropical cyclones (minor), were discussed. We utilized ERA5 reanalysis products (meteorology and O3) to trace and analyze the pathway and mechanism of these SI types over sub-tropical East Asia. With a conceptual model, we illustrate two driving circulations for SI air at ∼200 hPa that affect subtropical East Asia. SI air generated due to Rossby wave breaks are transported equatorward and downward into the troposphere. The southern westerlies passing south of the Tibetan Plateau can further push the SI air eastward. A SI event in 2007 with a significant O3 enhancement of 43.4 ppb caused by typhoon Nari was detected and discussed to depict the second SI type.

Despite many demonstrated benefits that biochars can have on agricultural soils, there are few examples of profitable biochar utilization on commercial farms. Barriers to profitability include successfully pairing waste streams, production facilities, and farms where biochar is utilized. However, farm-scale biochar systems, which utilize agricultural wastes as feedstocks and produce energy and biochar for on-farm use, may have efficiency advantages over regional, industrial biochar production. Two critical uncertainties for the feasibility of on-farm production are 1) whether a biochar can be produced from on-farm feedstocks with appropriate qualities for soil amendment, and 2) whether on-farm feedstocks are sufficiently abundant to meet on-farm demand. Here we evaluate these issues for a farm-scale gasification system in NE Washington State that produces biochar from grass seed screenings and straw. Field trials to evaluate the biochar as a liming alternative found it was highly effective when broadcast at a rate of at least 18 Mg ha−1. Biochar outperformed hydrated lime in the first year of the study and improved yields by a factor of 2.88 across both years. Biochar produced from on-farm feedstocks were sufficient to amend 6.3–11.8% of the production area annually, translating to a return interval of 9–16 years. Potential co-production of electrical power far exceeded on-farm demand for operating a seed cleaning mill. We conclude that an on-farm biochar production system is physically feasible for meeting demands for both power and liming amendments.

In this study, the trends and factors influencing wintertime precipitation chemistry at a remote site downwind of continental East Asia were investigated. A total of 336 precipitation samples were collected from 2005 to 2019 at Pengjia Islet, a site ~56 km north of the main island of Taiwan. Overall, the samples had a volume-weighted mean pH of 4.81 (ranging from 3.03 to 7.00), with 74% of samples considered as acid rain (pH

The formation of sulfate (SO42−) in the atmosphere is linked chemically to its direct precursor, sulfur dioxide (SO2), through several key oxidation paths for which nitrogen oxides or NOx (NO and NO2) play essential roles. Here we present a coherent description of the dependence of SO42– formation on SO2 and NOx under haze-fog conditions, in which fog events are accompanied by high aerosol loadings and fog-water pH in the range of 4.7–6.9. Three SO42– formation regimes emerge as defined by the role played by NOx. In the low-NOx regime, NOx act as catalyst for HOx, which is a major oxidant for SO2, whereas in the high-NOx regime, NO2 is a sink for HOx. Moreover, at highly elevated NOx levels, a so-called NO2-oxidant regime exists in which aqueous NO2 serves as the dominant oxidant of SO2. This regime also exists under clean fog conditions but is less prominent. Sensitivity calculations using an emission-driven box model show that the reduction of SO42– is comparably sensitive to the reduction of SO2 and NOx emissions in the NO2-oxidant regime, suggesting a co-reduction strategy. Formation of SO42− is relatively insensitive to NOx reduction in the low-NOx regime, whereas reduction of NOx actually leads to increased SO42– production in the intermediate high-NOx regime. Distinct dependence of atmospheric SO42– formation on NOx levels in haze-fog events is revealed by SO42– production isopleths that are obtained through simulations of atmospheric chemistry with a box model.

East Asian Dust (EAD) has had a measurable impact on global climate and air quality, including visibility and human health, in numerous locations around the globe over the past decade. The accuracy of an air quality modeling system to simulate dust events is vital for early warning systems. The most significant dust event observed in 6 years for northern Taiwan occurred during 4th–9th April 2018, and was characterized by high wind speeds (9–13 m s−1) upon arrival to the region. We assessed the windblown dust emission treatment across various modifications and found better model performance by decreasing the soil moisture factor and updating the aerosol speciation profile over East Asia. In the optimized CMAQ simulation, uplifted dust particles reached a maximum height of 500–700 hPa, which is crucial for effective transport of the dust plume to the downwind Taiwan region. However, by tracking the vertical distribution profile, we found the model was insufficient to estimate dust aerosol after exiting from over the continent and entering the marine boundary layer. Our simulation indicated the dust event consisted of two plumes, where the first one was significantly impacted by wet deposition (−70.65%) from a rainfall belt stretching across Japan, Korea and the East China Sea. Then, low wind speed during a period of no precipitation over the marine area led to even greater dust deposition (−89.11%) from the second plume, resulting in a consistent negative bias for the simulation. This modeling study highlights the importance of improving the dust emission treatment for a better simulation of dust aerosol transport over the marine boundary layer. To reduce the uncertainty in the dust outflow region, the deposition mechanisms for the CMAQ dust treatment should be revised.

Gas-phase biogenic volatile organic compounds (BVOCs) are oxidized in the troposphere to produce secondary pollutants such as ozone (O3), organic nitrates (RONO2), and secondary organic aerosol (SOA). Two coupled zero-dimensional models have been used to investigate differences in oxidation and SOA production from isoprene and α-pinene, especially with respect to the nitrate radical (NO3), above and below a forest canopy in rural Michigan. In both modeled environments (above and below the canopy), NO3 mixing ratios are relatively small (3 contributes 12 % of total daytime α-pinene oxidation below the canopy while only contributing 4 % above. Increasing background pollutant levels to simulate a more polluted suburban or peri-urban forest environment increases the average contribution of NO3 to daytime below-canopy α-pinene oxidation to 32 %. Gas-phase RONO2 produced through NO3 oxidation undergoes net transport upward from the below-canopy environment during the day, and this transport contributes up to 30 % of total NO3-derived RONO2 production above the canopy in the morning (∼ 07:00). Modeled SOA mass loadings above and below the canopy ultimately differ by less than 0.5 µg m−3, and extremely low-volatility organic compounds dominate SOA composition. Lower temperatures below the canopy cause increased partitioning of semi-volatile gas-phase products to the particle phase and up to 35 % larger SOA mass loadings of these products relative to above the canopy in the model. Including transport between above- and below-canopy environments increases above-canopy NO3-derived α-pinene RONO2 SOA mass by as much as 45 %, suggesting that below-canopy chemical processes substantially influence above-canopy SOA mass loadings, especially with regard to monoterpene-derived RONO2.

Single Particle Aerosol Mass Spectrometers (SPAMS) have been increasingly deployed for aerosol studies in Asia. To date, SPAMS is most often used to provide unscaled information for both the size and chemical composition of individual particles. The instrument's lack of accuracy is primarily due to only a fraction of particles being detected after collection, and the instrumental sensitivity is un-calibrated for various chemical species in mixed ambient aerosols. During a campaign from January to April 2013 at a coastal site in Hong Kong, the particle number information and ion intensity of major PM 2.5 components collected by SPAMS were scaled by comparing with collocated bulk PM 2.5 measurements of hourly or higher resolution. The bulk measurements include PM 2.5 mass by a SHARP 5030 Monitor, major ions by a Monitor for Aerosols & Gases in ambient Air (MARGA), and organic carbon (OC) and elemental carbon (EC) by a Sunset OCEC analyzer. During the data processing, both transmission efficiency (scaled with the Scanning Mobility Particle Sizer) and hit efficiency conversion were considered, and component ion intensities quantified as peak area (PA) and relative peak area (RPA) were analyzed to track the performance. The comparison between the scaled particle mass assuming a particle density of 1.9 g cm −3 from SPAMS and PM 2.5 concentration showed good correlation (R 2 = 0.81) with a slope of 0.814 ± 0.004. Regression analysis results suggest an improved scaling performance using RPA compared with PA for most of the major PM 2.5 components, including sulfate, nitrate, potassium, ammonium, OC and EC. Thus, we recommend preferentially scaling these species using the RPA. For periods of high K + concentrations (>1.5 μg m −3 ), under-estimation of K + by SPAMS was observed due to exceeding the dynamic range of the acquisition board. When only applying the hit efficiency correction, data for sulfate, nitrate, ammonium, potassium and OC were in reasonably good correlation (R 2 = 0.56–0.79) with the bulk measurements, suggesting semi-quantified data by the hit efficiency correction can be utilized when transmission efficiency correction is not available. More inter-comparisons of this type are needed to assess the inter-instrument variability among different SPAMS instruments.

International audience; Measurements of hydroxyl (OH) and hydroperoxy (HO2*) radical concentrations were made at the Pasadena ground site during the CalNex-LA 2010 campaign using the laser-induced fluorescence-fluorescence assay by gas expansion technique. The measured concentrations of OH and HO2* exhibited a distinct weekend effect, with higher radical concentrations observed on the weekends corresponding to lower levels of nitrogen oxides (NOx). The radical measurements were compared to results from a zero-dimensional model using the Regional Atmospheric Chemical Mechanism-2 constrained by NOx and other measured trace gases. The chemical model overpredicted measured OH concentrations during the weekends by a factor of approximately 1.4 ± 0.3 (1σ), but the agreement was better during the weekdays (ratio of 1.0 ± 0.2). Model predicted HO2* concentrations underpredicted by a factor of 1.3 ± 0.2 on the weekends, while measured weekday concentrations were underpredicted by a factor of 3.0 ± 0.5. However, increasing the modeled OH reactivity to match the measured total OH reactivity improved the overall agreement for both OH and HO2* on all days. A radical budget analysis suggests that photolysis of carbonyls and formaldehyde together accounted for approximately 40% of radical initiation with photolysis of nitrous acid accounting for 30% at the measurement height and ozone photolysis contributing less than 20%. An analysis of the ozone production sensitivity reveals that during the week, ozone production was limited by volatile organic compounds throughout the day during the campaign but NOx limited during the afternoon on the weekends.

Long-range transport (LRT) of air pollutants from East Asia during the northeast monsoon season impacts several downwind locations. In 2020, the initial COVID-19 lockdowns in China overlapped with Week 3 of the Chinese New Year (CNY) holiday, and an Asian outflow event. Thus, movement of the Chinese populace from city to city was already greatly reduced by the time of the LRT episode, although the reductions in industrial output are less clear. We found NO2 column concentrations were reduced by 24% during the CNY Week 3 this year compared to previous years. The attenuated transport event arrived to northern Taiwan with a PM2.5 concentration, Graphical abstract Unlabelled Image, Highlights • COVID-19 lockdown in China reduced long-range transport of air pollution to Taiwan. • OMI NO2 over central-north China reduced by 24% compared to previous years. • PM2.5 concentration in northern Taiwan 2 times lower compared to similar episode • CMAQ simulation with 50% reduced emission in China matches measured PM2.5 in Taiwan. • Avoided PM2.5 pollution equivalent to 0.5 μg m−3 reduction for entire winter season

Semi-volatile and intermediate-volatility organic compounds (SVOCs and IVOCs) from anthropogenic sources are likely to be important precursors of secondary organic aerosol (SOA) in urban airsheds yet their treatment in most models is based on limited and obsolete data, or completely missing. Additionally, gas-phase oxidation of organic precursors to form SOA is influenced by the presence of nitric oxide (NO), but this influence is poorly constrained in chemical transport models. In this work, we updated the organic aerosol model in the UCD/CIT chemical transport model to include (i) a semi-volatile and reactive treatment of primary organic aerosol (POA), (ii) emissions and SOA formation from IVOCs, (iii) the NOX influence on SOA formation, and (iv) SOA parameterizations for SVOCs and IVOCs that are corrected for vapor wall loss artifacts during chamber experiments. All updates were implemented in the statistical oxidation model (SOM) that simulates the chemistry, thermodynamic properties, and gas/particle partitioning of organic aerosol (OA). Model treatment of POA, SVOCs, and IVOCs was based on an interpretation of a comprehensive set of source measurements and resolved broadly by source type. The NOX influence on SOA formation was calculated offline based on measured and modeled VOC:NOX ratios. And finally, the SOA formation from all organic precursors (including SVOCs and IVOCs) was modeled based on recently derived parameterizations that accounted for vapor wall loss artifacts in chamber experiments. The updated model was used to simulate a two week summer episode over southern California at a model resolution of 8 km. When combustion-related POA was treated as semi-volatile, modeled POA mass concentrations were reduced by 30–50 % in the urban areas in southern California but were still too high when compared against measurements made at Riverside, CA during the Study of Organic Aerosols at Riverside (SOAR-1) campaign of 2005. Treating all POA (except that from marine sources) to be semi-volatile resulted in a larger reduction in POA mass concentrations and allowed for a better model-measurement comparison at Riverside. Model predictions suggested that both SVOCs (evaporated POA vapors) and IVOCs did not contribute significantly to SOA mass concentrations in the urban areas (

Many aromatic compounds (e.g., polycyclic aromatic hydrocarbons (PAHs)) found in atmospheric aerosols are toxic and exist in both unsubstituted and substituted forms. Previous studies have mainly concentrated on investigating unsubstituted PAHs, leaving the substituted compounds largely uncharacterized. This study focuses on detection of both unsubstituted and substituted aromatics in ambient aerosol samples using ultrahigh-resolution mass spectrometry. Aerosol samples collected from roadside, urban, and suburban sites in Hong Kong were characterized by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) coupled with atmospheric pressure photoionization (APPI) or electrospray ionization (ESI). In the APPI+ mode, 166 aromatic CH formulas (i.e., formulas containing C and H only and with a double bond equivalent (DBE) of 4 or higher) were determined through molecular formula calculations based on an accurate m/z determination. Among the determined aromatic CH formulas, 141 are possible alkylated monocyclic aromatic hydrocarbon (MAH) or PAH formulas, and account for ≥ 45% of the total intensity by aromatic CH+ formulas. Both APPI+ and ESI+ are effective in detecting nitroaromatics (i.e., CHO

In this study, we investigated the seasonal, diurnal, and episodic characteristics of aerosol nitrate concentrations in PM2.5 at a suburban receptor site in Hong Kong using an hourly MARGA sampled dataset. At the site, large spikes in the NO3− concentration have been observed in all seasons, and are easily overlooked in datasets examining 24 h average concentrations. As a key component to PM2.5, nitrate constituted between 5 and 12% of the mass concentration on average per month, but contributed up to 25% during some episodic cases spanning only a few hours. Seasonal variations of PM2.5 nitrate concentrations at the site were driven by temperature and excess [NH4+] in the aerosol, defined as the amount of ammonium in excess of that required for satisfying [NH4+]/[SO42−] = 1.5. The vast majority of winter nitrate data was associated with ammonium-rich aerosols ([NH4+]/[SO42−] > 1.5), with the diurnal variation tracking the availability of excess [NH4+]. Distinctly different than winter conditions, the summer nitrate data was in ammonium-poor regime and tracked nitric acid concentrations, a photochemical tracer. A regression analysis of measured nitrate with the excess [NH4+] shows good correlation in spring, summer and winter (R2: 0.72–0.81), with slopes greater than 0.7 indicating the majority of excess NH4+ is associated with PM2.5 nitrate. It was found that measured nitrate exceeded excess [NH4+] in samples of low excess [NH4+] availability, leading to our finding that nitric acid attaching to sea salt and crustal particles in the fine mode is a non-negligible route (constituting up to ∼20% of the PM2.5 nitrate in this study) to assimilate nitrate into the PM2.5 aerosol. Accounting for both this minor route and the ammonia + nitric acid route may prove useful in modeling efforts to capture PM2.5 nitrate measurement fluctuations, particularly during events of a large influx of alkali particles, such as dust storms.

Successful development of approaches to quantify impacts of diverse landuse and associated agricultural management practices on ecosystem services is frequently limited by lack of historical and contemporary landuse data. We hypothesized that ground truth data from one year could be used to extrapolate previous or future landuse in a complex landscape where cropping systems do not generally change greatly from year to year because the majority of crops are established perennials or the same annual crops grown on the same fields over multiple years. Prior to testing this hypothesis, it was first necessary to classify 57 major landuses in the Willamette Valley of western Oregon from 2005 to 2011 using normal same year ground-truth, elaborating on previously published work and traditional sources such as Cropland Data Layers (CDL) to more fully include minor crops grown in the region. Available remote sensing data included Landsat, MODIS 16-day composites, and National Aerial Imagery Program (NAIP) imagery, all of which were resampled to a common 30 m resolution. The frequent presence of clouds and Landsat7 scan line gaps forced us to conduct of series of separate classifications in each year, which were then merged by choosing whichever classification used the highest number of cloud- and gap-free bands at any given pixel. Procedures adopted to improve accuracy beyond that achieved by maximum likelihood pixel classification included majority-rule reclassification of pixels within 91,442 Common Land Unit (CLU) polygons, smoothing and aggregation of areas outside the CLU polygons, and majority-rule reclassification over time of forest and urban development areas. Final classifications in all seven years separated annually disturbed agriculture, established perennial crops, forest, and urban development from each other at 90 to 95% overall 4-class validation accuracy. In the most successful use of subsequent year ground-truth data to classify prior year landuse, an overall 57-class accuracy of 75% was achieved despite the omission of 10 entire classes, most of which were annually disturbed or perennial crops grown on very few fields. Synthetic ground-truth data for the 2004 harvest year based on the most common landuse classes over the following 7 years classified 49 of 57 categories at an overall accuracy of 96% in a final version that included CLU polygon majority rule, default smoothing and aggregation, and forcing of urban development and forest from multi-year majority-rule.

Organic carbon (OC) and elemental carbon (EC) are operationally defined by analytical methods. As a result, OC and EC measurements are protocol dependent, leading to uncertainties in their quantification. In this study, more than 1300 Hong Kong samples were analyzed using both National Institute for Occupational Safety and Health (NIOSH) thermal optical transmittance (TOT) and Interagency Monitoring of Protected Visual Environment (IMPROVE) thermal optical reflectance (TOR) protocols to explore the cause of EC disagreement between the two protocols. EC discrepancy mainly (83 %) arises from a difference in peak inert mode temperature, which determines the allocation of OC4NSH, while the rest (17 %) is attributed to a difference in the optical method (transmittance vs. reflectance) applied for the charring correction. Evidence shows that the magnitude of the EC discrepancy is positively correlated with the intensity of the biomass burning signal, whereby biomass burning increases the fraction of OC4NSH and widens the disagreement in the inter-protocol EC determination. It is also found that the EC discrepancy is positively correlated with the abundance of metal oxide in the samples. Two approaches (M1 and M2) that translate NIOSH TOT OC and EC data into IMPROVE TOR OC and EC data are proposed. M1 uses direct relationship between ECNSH_TOT and ECIMP_TOR for reconstruction: M1 : ECIMP_TOR = a × ECNSH_TOT + b; while M2 deconstructs ECIMP_TOR into several terms based on analysis principles and applies regression only on the unknown terms: M2 : ECIMP_TOR = AECNSH + OC4NSH − (a × PCNSH_TOR + b), where AECNSH, apparent EC by the NIOSH protocol, is the carbon that evolves in the He–O2 analysis stage, OC4NSH is the carbon that evolves at the fourth temperature step of the pure helium analysis stage of NIOSH, and PCNSH_TOR is the pyrolyzed carbon as determined by the NIOSH protocol. The implementation of M1 to all urban site data (without considering seasonal specificity) yields the following equation: M1(urban data) : ECIMP_TOR = 2.20 × ECNSH_TOT − 0.05. While both M1 and M2 are acceptable, M2 with site-specific parameters provides the best reconstruction performance. Secondary OC (SOC) estimation using OC and EC by the two protocols is compared. An analysis of the usability of reconstructed ECIMP_TOR and OCIMP_TOR suggests that the reconstructed values are not suitable for SOC estimation due to the poor reconstruction of the OC / EC ratio.

We analyze an expanded data set of oxygenated volatile organic compounds (OVOCs) in air measured by several instruments at a surface site in Pasadena near Los Angeles during the National Oceanic and Atmospheric Administration California Nexus study in 2010. The contributions of emissions, chemical formation, and removal are quantified for each OVOC using CO as a tracer of emissions and the OH exposure of the sampled air masses calculated from hydrocarbon ratios. The method for separating emissions from chemical formation is evaluated using output for Pasadena from the Weather Research and Forecasting-Chemistry model. The model is analyzed by the same method as the measurement data, and the emission ratios versus CO calculated from the model output agree for ketones with the inventory used in the model but overestimate aldehydes by ~70%. In contrast with the measurements, nighttime formation of OVOCs is significant in the model and is attributed to overestimated precursor emissions and overestimated rate coefficients for the reactions of the precursors with ozone and NO3. Most measured aldehydes correlated strongly with CO at night, suggesting a contribution from motor vehicle emissions. However, the emission ratios of most aldehydes versus CO are higher than those reported in motor vehicle emissions and the aldehyde sources remain unclear. Formation of several OVOCs is investigated in terms of the removal of specific precursors. Direct emissions of alcohols and aldehydes contribute significantly to OH reactivity throughout the day, and these emissions should be accurately represented in models describing ozone formation. ©2018. American Geophysical Union. All Rights Reserved.

Liquid water content (LWC) is the amount of liquid water on aerosols. It contributes to visibility degradation, provides a surface for gas condensation, and acts as a medium for heterogeneous gas/particle reactions. In this study, 520 half-hourly measurements of ionic chemical composition in PM2.5 at a receptor site in Hong Kong are used to investigate the dependence of LWC on ionic chemical composition, particularly on the relative abundance of sulfate and nitrate. LWC was estimated using a thermodynamic model (AIM-III). Within this data set of PM2.5 ionic compositions, LWC was highly correlated with the multivariate combination of sulfate and nitrate concentrations and RH (R2 = 0.90). The empirical linear regression result indicates that LWC is more sensitive to nitrate mass than sulfate. During a nitrate episode, the highest LWC (80.6 ± 17.9 μg m−3) was observed and the level was 70% higher than that during a sulfate episode despite a similar ionic PM2.5 mass concentration. A series of sensitivity tests were conducted to study LWC change as a function of the relative nitrate and sulfate abundance, the trend of which is expected to shift to more nitrate in China as a result of SO2 reduction and increase in NOx emission. Starting from a base case that uses the average of measured PM2.5 ionic chemical composition (63% SO42−, 11% NO3−, 19% NH4+, and 7% other ions) and an ionic equivalence ratio, [NH4+]/(2[SO42−] + [NO3−]), set constant to 0.72, the results show LWC would increase by 204% at RH = 40% when 50% of the SO42− is replaced by NO3− mass concentration. This is largely due to inhibition of (NH4)3H(SO4)2 crystallization while PM2.5 ionic species persist in the aqueous phase. At RH = 90%, LWC would increase by 12% when 50% of the SO42− is replaced by NO3− mass concentration. The results of this study highlight the important implications to aerosol chemistry and visibility degradation associated with LWC as a result of a shift in PM2.5 ionic chemical composition to more nitrate in atmospheric environments as is expected in many Chinese cities.

Total hydroxyl radical (OH) reactivity was measured at the PROPHET (Program for Research on Oxidants: PHotochemistry, Emissions, and Transport) forested field site in northern Michigan during the 2009 Community Atmosphere–Biosphere INteraction EXperiment (CABINEX). OH reactivity measurements were made with a turbulent-flow reactor instrument at three heights from the forest floor above (21 and 31 m) and below (6 m) the canopy at three different time periods during the CABINEX campaign. In addition to total OH reactivity measurements, collocated measurements of volatile organic compounds (VOCs), inorganic species, and ambient temperature were made at the different heights. These ancillary measurements were used to calculate the total OH reactivity, which was then compared to the measured values. Discrepancies between the measured and calculated OH reactivity, on the order of 1–24 s−1, were observed during the daytime above the canopy at the 21 and 31 m heights, as previously reported for this site. The measured OH reactivity below the canopy during the daytime was generally lower than that observed above the canopy. Closer analysis of the measurements of OH reactivity and trace gases suggests that the missing OH reactivity could come from oxidation products of VOCs. These results suggest that additional unmeasured trace gases, likely oxidation products, are needed to fully account for the OH reactivity measured during CABINEX.

Research on relationships between dissolved nutrients and land-use at the watershed scale is a high priority for protecting surface water quality. We measured dissolved nitrogen (DN) and ortho-phosphorus (P) along 130 km of the Calapooia River (Oregon, USA) and 44 of its sub-basins for 3 years to test for associations with land-use. Nutrient concentrations were analyzed for spatial and seasonal patterns and for relationships with land-use and stream discharge. Ortho-P and DN were higher in lower-elevation sub-basins dominated by poorly drained soils and agricultural production compared with higher-elevation sub-basins dominated by well-drained soils and forests. Eight lower basins had at least one sample period with nitrate-N 10 mg L(-1). The Calapooia River had lower concentrations of dissolved nutrients compared with lower sub-basins, often by an order of magnitude. Dissolved organic N represented a greater proportion of DN in the upper forested sub-basins. Seasonal nutrient concentrations had strong positive correlations to the percent of a sub-basin that was managed for agriculture in all seasons (p values ≤ 0.019) except summer. Results suggest that agricultural lands are contributing to stream nutrient concentrations. However, poorly drained soils in agricultural areas may also contribute to the strong relationships that we found between dissolved nutrients and agriculture.

[1] Organic aerosols (OA) in Pasadena are characterized using multiple measurements from the California Research at the Nexus of Air Quality and Climate Change (CalNex) campaign. Five OA components are identified using positive matrix factorization including hydrocarbon-like OA (HOA) and two types of oxygenated OA (OOA). The Pasadena OA elemental composition when plotted as H : C versus O : C follows a line less steep than that observed for Riverside, CA. The OOA components from both locations follow a common line, however, indicating similar secondary organic aerosol (SOA) oxidation chemistry at the two sites such as fragmentation reactions leading to acid formation. In addition to the similar evolution of elemental composition, the dependence of SOA concentration on photochemical age displays quantitatively the same trends across several North American urban sites. First, the OA/ΔCO values for Pasadena increase with photochemical age exhibiting a slope identical to or slightly higher than those for Mexico City and the northeastern United States. Second, the ratios of OOA to odd-oxygen (a photochemical oxidation marker) for Pasadena, Mexico City, and Riverside are similar, suggesting a proportional relationship between SOA and odd-oxygen formation rates. Weekly cycles of the OA components are examined as well. HOA exhibits lower concentrations on Sundays versus weekdays, and the decrease in HOA matches that predicted for primary vehicle emissions using fuel sales data, traffic counts, and vehicle emission ratios. OOA does not display a weekly cycle—after accounting for differences in photochemical aging —which suggests the dominance of gasoline emissions in SOA formation under the assumption that most urban SOA precursors are from motor vehicles.

Seed mill screenings would be a considerable biofeedstock source for bioenergy and char production. Char produced from the gasification of residues resulting from cleaning of grass seed and small grains could be recycled to a cropping system as a soil amendment if chemical characterization determined that the gasification process had not produced or concentrated deleterious chemical or physical factors that might harm the environment, crop growth or yield. Previous reports have shown that char derived from the pyrolysis of a variety of biomass feedstocks has potential to enhance soil quality by pH adjustment, mineral amendment, and improved soil porosity. The objective of this research was to characterize char produced from Kentucky bluegrass seed mill screenings (KBss) by a small-scale gasification unit, operated at temperatures between 600 and 650 °C, with respect to polycyclic aromatic hydrocarbons, selected heavy metals, as well as other physical and chemical characteristics, and determine its suitability for agricultural application as a soil amendment. We utilized KBss as a model for seed and grain-cleaning residues with the understanding that chemical and physical characteristics of char produced by gasification or other cleaning residues may differ based on soil and environmental conditions under which the crops were produced. Our results support the hypothesis that KBss char could be applied in a cropping system without toxic environmental consequences and serve multiple purposes, such as; recycling critical plant macro- and micro-nutrients back to existing cropland, enhancing soil carbon sequestration, managing soil pH, and improving water holding capacity. Crop field trails need to be implemented to further test these hypotheses.

Hydroxyl (OH) and hydroperoxyl (HO2) radicals are key species driving the oxidation of volatile organic compounds that can lead to the production of ozone and secondary organic aerosols. Previous measurements of these radicals in forest environments with high isoprene, low NOx conditions have shown serious discrepancies with modeled concentrations, bringing into question the current understanding of isoprene oxidation chemistry in these environments. During the summers of 2008 and 2009, OH and peroxy radical concentrations were measured using a laser-induced fluorescence instrument as part of the PROPHET (Program for Research on Oxidants: PHotochemistry, Emissions, and Transport) and CABINEX (Community Atmosphere-Biosphere INteractions EXperiment) campaigns at a forested site in northern Michigan. Supporting measurements of photolysis rates, volatile organic compounds, NOx (NO + NO2 and other inorganic species were used to constrain a zero-dimensional box model based on the Regional Atmospheric Chemistry Mechanism, modified to include the Mainz Isoprene Mechanism (RACM-MIM). The CABINEX model OH predictions were in good agreement with the measured OH concentrations, with an observed-to-modeled ratio near one (0.70 ± 0.31) for isoprene mixing ratios between 1–2 ppb on average. The measured peroxy radical concentrations, reflecting the sum of HO2 and isoprene-based peroxy radicals, were generally lower than predicted by the box model in both years.

Gas-phase biogenic volatile organic compounds (BVOCs) are oxidized in the troposphere to produce secondary pollutants such as ozone (O3), organic nitrates (RONO2), and secondary organic aerosol (SOA). The nitrate radical (NO3) is especially reactive towards isoprene and monoterpenes such as α-pinene. A zero-dimensional model has been used to investigate differences in oxidation and SOA production from these two BVOCs, especially with respect to hydroxyl radical (OH) and NO3, above and below a forest canopy in rural Michigan using local data and data from a monitoring site in Detroit. In all modeled scenarios, NO3 concentrations are relatively small (0.5–3 pptv); however, daytime concentrations below the canopy are two-to-three times larger than those above. In the rural scenario, NO3 contributes up to 20 % of daytime oxidation of α-pinene below the canopy, and this contribution increases to around 40 % in the polluted cases. Oxidation of isoprene is almost entirely dominated by reaction with OH, as expected. The most significant first-generation RONO2 formation mechanism varies significantly between scenarios and by canopy location. Nonetheless, in every scenario, daytime production of first-generation RONO2 through NO3 + α-pinene is more significant below the canopy than above. While SOA mass loadings are moderate (2 μg m−3 or less), total SOA production is consistently enhanced below the canopy, due to the combined effects of elevated isoprene and reduced NO concentrations. Furthermore, below the canopy, the total amount of RONO2 SOA produced through NO3 oxidation of α-pinene during the daytime (10:00–18:00), while small in absolute terms, is more than twice as large as the amount produced above the canopy during that time period in every scenario. In the rural ambient case, a minimum of 74 % of α-pinene RONO2 SOA is formed solely from initial oxidation by NO3. The relative abundances of HO2 and NO are shown to substantially impact both total SOA production and RONO2 SOA composition. The results presented emphasize the need for more detailed studies regarding the influence of NO3 throughout forest canopies in different environments.

Vegetation emits large quantities of biogenic volatile organic compounds (BVOC). At remote sites, these compounds are the dominant precursors to ozone and secondary organic aerosol (SOA) production, yet current field studies show that atmospheric models have difficulty in capturing the observed HOx cycle and concentrations of BVOC oxidation products. In this manuscript, we simulate BVOC chemistry within a forest canopy using a one-dimensional canopy-chemistry model (Canopy Atmospheric CHemistry Emission model; CACHE) for a mixed deciduous forest in northern Michigan during the CABINEX 2009 campaign. We find that the base-case model, using fully-parameterized mixing and the simplified biogenic chemistry of the Regional Atmospheric Chemistry Model (RACM), underestimates daytime in-canopy vertical mixing by 50–70% and by an order of magnitude at night, leading to discrepancies in the diurnal evolution of HOx, BVOC, and BVOC oxidation products. Implementing observed micrometeorological data from above and within the canopy substantially improves the diurnal cycle of modeled BVOC, particularly at the end of the day, and also improves the observation-model agreement for some BVOC oxidation products and OH reactivity. We compare the RACM mechanism to a version that includes the Mainz isoprene mechanism (RACM-MIM) to test the model sensitivity to enhanced isoprene degradation. RACM-MIM simulates higher concentrations of both primary BVOC (isoprene and monoterpenes) and oxidation products (HCHO, MACR+MVK) compared with RACM simulations. Additionally, the revised mechanism alters the OH concentrations and increases HO2. These changes generally improve agreement with HOx observations yet overestimate BVOC oxidation products, indicating that this isoprene mechanism does not improve the representation of local chemistry at the site. Overall, the revised mechanism yields smaller changes in BVOC and BVOC oxidation product concentrations and gradients than improving the parameterization of vertical mixing with observations, suggesting that uncertainties in vertical mixing parameterizations are an important component in understanding observed BVOC chemistry.

Agricultural practices, including tillage, fertilization, and residue management, can affect surface runoff, soil erosion, and nutrient cycling. These processes, in turn, may adversely affect (1) quality of aquatic resources as habitat for amphibians, fish, and invertebrates, (2) costs of treating surface and ground water to meet drinking water standards, and (3) large-scale biogeochemistry. This study characterized the surface water sources of nitrogen (N) (total, nitrate (NO 3 − ), ammonium (NH 4 + ), and dissolved organic N) and sediment active within 40 subbasins of the Calapooia River Basin in western Oregon in monthly samples over three cropping years. The subbasins included both independent and nested drainages, with wide ranges in tree cover, agricultural practices, slopes, and soils. Sediment and N form concentra- tions were tested against weather and agricultural practice variables. Subbasin land use ranged from 96% forest to 100% agriculture. Average slopes varied from 1.3% to 18.9%, and surface water quality ranged from 0.5 to 43 mg L -1 (ppm) total N maxima and 29 to 249 mg L -1 suspended sediment maxima. Total N during the winter was positively related to percentage landcover of seven common agricultural crops (nongrass seed summer annuals, established seed crops of perennial ryegrass (Lolium perenne L.), tall fescue (Schedonorus phoenix {Scop.} Holub), orchardgrass (Dactylis glomerata L.), clover (Trifolium spp.), and newly planted stands of perennial ryegrass and clover) and negatively related to cover by trees and one seed crop, Italian (annual) ryegrass (Lolium multiflorum). Results for NO 3 − and total N were highly simi- lar. Sediment concentrations were most strongly related to rainfall totals during periods of 4 and 14 days prior to sampling, with smaller effects of soil disturbance. Fourier analysis of total N over time identified four prominent groups of subbasins: those with (1) low, (2) medium, and (3) high impacts of N (up to 2, 8, and 21 mg L -1 , respectively) and a strong cyclical signal peaking in December and (4) those with very high impact of N (up to 43 mg L -1 ) and a weak time series signal. Preponderance of N in streams draining agriculturally dominated subbasins was in the form of the NO 3 − ion, implying mineralization of N that had been incorporated within plant tissue following its initial application in the spring as urea-based fertilizer. Since mineralization is driven by seasonal rainfall and temperature patterns, changes in agronomic practices designed to reduce prompt runoff of fertilizer are unlikely to achieve to more than ~24% reduction in N export to streams.

We reanalyze a data set of hydrocarbons in ambient air obtained by gas chromatography-mass spectrometry at a surface site in Pasadena in the Los Angeles basin during the NOAA California Nexus study in 2010. The number of hydrocarbon compounds quantified from the chromatograms is expanded through the use of new peak-fitting data analysis software. We also reexamine hydrocarbon removal processes. For alkanes, small alkenes, and aromatics, the removal is determined by the reaction with hydroxyl (OH) radicals. For several highly reactive alkenes, the nighttime removal by ozone and nitrate (NO3) radicals is also significant. We discuss how this nighttime removal affects the determination of emission ratios versus carbon monoxide (CO) and show that previous estimates based on nighttime correlations with CO were too low. We analyze model output from the Weather Research and Forecasting-Chemistry model for hydrocarbons and radicals at the Pasadena location to evaluate our methods for determining emission ratios from the measurements. We find that our methods agree with the modeled emission ratios for the domain centered on Pasadena and that the modeled emission ratios vary by 23% across the wider South Coast basin. We compare the alkene emission ratios with published results from ambient measurements and from tunnel and dynamometer studies of motor vehicle emissions. We find that with few exceptions the composition of alkene emissions determined from the measurements in Pasadena closely resembles that of motor vehicle emissions.

The objective of this research was the development of a method that integrated an activity analysis model of profits from production with a biophysical model, and included the capacity for optimization over multiple objectives. We specified a hybrid genetic algorithm using activity analysis as a local search method, and NSGA-II for calculation of the multiple objective Pareto optimal set. We describe a parallel computing approach to computation of the genetic algorithm, and apply the algorithm to evaluation of an input tax to regulate pollution from agricultural production.