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Nitryl chloride (ClNO2) has been reported as a critical species of chlorine chemistry. Its chemistry interrupts a nighttime sink of NOX and emits chlorine radical (Cl•) in the daytime, consequently altering gaseous and aerosol chemistry. Recent field studies have also measured considerable concentrations of ClNO2 in South Korea under the influences of natural and anthropogenic chlorine sources. However, the impacts of ClNO2 chemistry on air quality in South Korea have yet to be evaluated. We validate simulated ClNO2 and its chemistry in South Korea using observations and a 3-D chemical transport model (CTM) during the Korea-United States Air Quality field study. We implemented the latest Chinese and Korean anthropogenic chlorine emissions in the model. We found that the model reproduces the observed spatial and temporal variations of ClNO2, including its local and transboundary transport and precursors. We found that ClNO2 chemistry results in a more efficient conversion of NO to NO2 at night and daytime acceleration of the NOX-O3 cycle. It results in an increase of O3 (1.1%), NOX (3.1%), OH (2.0%), HO2 (0.8%), and Cl• (507.8%) and a decrease of TNO3(HNO3 + aerosol nitrate, 1.7%) on the campaign mean basis.

Four different plant species, sunflower (Helianthus annuus), western redcedar (Thuja plicata), American sweetgum (Liquidambar styraciflua), and red ironbark (Eucalyptus sideroxylon), were enclosed in glass or Teflon chambers, exposed to different temperatures typically ranging from 30 °C to 43 °C, and their terpenoid emission rates were quantified using gas chromatography techniques. The results show that sunflower, western redcedar, and American sweetgum were not significant constitutive monoterpene emitters at 30 °C. Monoterpene emissions from western redcedar and American sweetgum remained negligibly low up to 35 °C–37 °C, however, at higher temperatures, the emissions began to increase at a much more rapid rate than predicted by current emission models. The monoterpene emissions from sunflower, western redcedar, and American sweetgum increased by an average factor of 22, 98, and 5900 for a temperature increase (ΔT) of 13 °C, 13 °C, and 15 °C, respectively, thereby transforming them from negligible into high monoterpene emitters. The observed emission increase was substantially higher than the model-predicted increase of 3.7-fold (ΔT = 13 °C) and 4.5-fold (ΔT = 15 °C). We demonstrate that current emission algorithms cannot accurately model the emission behavior of these plant species at the high temperatures that are characteristic of severe heatwaves. Furthermore, monoterpene emissions from western redcedar and American sweetgum remained elevated for 1–7 days after the heat stress. In contrast to the other three species, red ironbark was a significant constitutive monoterpene emitter (at 30 °C) and its emission response to temperature was close to model predictions. Each of the four species investigated in this study possesses specialized foliar terpene-storing structures, for example, glandular trichomes and oil glands. The strong monoterpene emission induction observed in some of these species may be attributed to heat-induced damage to these storage structures. However, the wall permeability of these structures may vary by species and could limit the magnitude of the heat-induced emission response., The research work presented in this paper was financially supported by the US National Science Foundation [award no: AGS-1643042]. RS acknowledges grants RYC2020-029216-I and CEX2018-000794-S funded by the Spanish Ministry of Science and Innovation and the State Research Agency (MCIN/AEI/ 10.13039/501100011033) and by the European Social Fund “ESF Investing in your future”.

A compound was observed using airborne proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) measurements in the emission plumes from the Daesan petrochemical facility in South Korea. The compound was detected at m/z 43.018 on the PTR-TOF-MS and was tentatively identified as ketene, a rarely measured reactive volatile organic compound (VOC). Estimated ketene mixing ratios as high as ∼ 50 ppb (parts per billion) were observed in the emission plumes. Emission rates of ketene from the facility were estimated using a horizontal advective flux approach and ranged from 84–316 kg h−1. These emission rates were compared to the emission rates of major known VOCs such as benzene, toluene, and acetaldehyde. Significant correlations (r2 > 0.7) of ketene with methanol, acetaldehyde, benzene, and toluene were observed for the peak emissions, indicating commonality of emission sources. The calculated average ketene OH reactivity for the emission plumes over Daesan ranged from 3.33–7.75 s−1, indicating the importance of the quantification of ketene to address missing OH reactivity in the polluted environment. The calculated average O3 production potential for ketene ranged from 2.98–6.91 ppb h−1. Our study suggests that ketene, or any possible VOC species detected at m/z 43.018, has the potential to significantly influence local photochemistry, and therefore, further studies focusing on the photooxidation and atmospheric fate of ketene through chamber studies are required to improve our current understanding of VOC OH reactivity and, hence, tropospheric O3 production.

In this study, two top-down methods-mass balance and Gaussian footprint-were used to determine SO

As the observational constraints of SO2 become a limiting factor for emission inventory and regional and global transport model validations, we present an airborne SO2 observational suite integrated on Beechcraft 1900D (B1900D) operated by Hanseo University. A chemical ionization mass spectrometry (CIMS) technique using SF6- ion chemistry is used to take advantage of fast response (

Emissions and secondary photochemical products from the Daesan petrochemical complex (DPCC), on the west coast of South Korea, were measured from the NASA DC-8 research aircraft during the Korea-United States Air Quality campaign in 2016. The chemical evolution of petrochemical emissions was examined utilizing near-source and downwind plume transects. Small alkenes, such as ethene (C2H4), propene (C3H6), and 1,3-butadiene (C4H6), dominated the hydroxyl (OH) radical reactivity near the source region. The oxidation of these alkenes in the petrochemical plumes led to efficient conversion of nitrogen oxides (NOx) to nitric acid (HNO3), peroxycarboxylic nitric anhydrides (PANs), and alkyl nitrates (ANs), where the sum of the speciated reactive nitrogen contributes more than 80% of NOy within a few hours. Large enhancements of short-lived NOx oxidation products, such as hydroxy nitrates (HNs) and peroxyacrylic nitric anhydride, were observed, in conjunction with high ozone levels of up to 250 ppb, which are attributed to oxidation of alkenes such as 1,3-butadiene. Instantaneous ozone production rates, P(O3), near and downwind of the DPCC ranged from 9 to 24 ppb h−1, which were higher than those over Seoul. Ozone production efficiencies ranged from 6 to 10 downwind of the DPCC and were lower than 10 over Seoul. The contributions of alkenes to the instantaneous secondary organic aerosol (SOA) production rate, P(SOA), were estimated to be comparable to those of more common SOA precursors such as aromatics at intermediate distances from the DPCC. A model case study constrained to an extensive set of observations provided a diagnostic of petrochemical plume chemistry. The simulated plume chemistry reproduced the observed evolution of ozone and short-lived reactive nitrogen compounds, such as PANs and HNs as well as the rate and efficiency of ozone production. The simulated peroxy nitrates (PNs) budget included large contributions (approximately 30%) from unmeasured PNs including peroxyhydroxyacetic nitric anhydride and peroxybenzoic nitric anhydride. The large, predicted levels of these PAN compounds suggest their potential importance in chemical evolution of petrochemical plumes. One unique feature of the DPCC plumes is the substantial contribution of 1,3-butadiene to ozone and potentially SOA production. This work suggests that reductions in small alkene, especially 1,3-butadiene, emissions from the DPCC should be a priority for reducing downwind ozone.

Isotopes are essential tools to apportion major sources of aerosols. We measured the radiocarbon, stable carbon, and stable nitrogen isotopic composition of PM2.5 at Taehwa Research Forest (TRF) near Seoul Metropolitan Area (SMA) during August-October 2014. PM2.5, TC, and TN concentrations were 19.4 ± 10.1 μg m-3, 2.6 ± 0.8 μg C m-3, and 1.4 ± 1.4 μg N m-3, respectively. The δ13C of TC and the δ15N of TN were - 25.4 ± 0.7‰ and 14.6 ± 3.8‰, respectively. EC was dominated by fossil-fuel sources with Fff (EC) of 78 ± 7%. In contrast, contemporary sources were dominant for TC with Fc (TC) of 76 ± 7%, revealing the significant contribution of contemporary sources to OC during the growing season. The isotopic signature carries more detailed information on sources depending on air mass trajectories. The urban influence was dominant under stagnant condition, which was in reasonable agreement with the estimated δ15N of NH4+. The low δ15N (7.0 ± 0.2‰) with high TN concentration was apparent in air masses from Shandong province, indicating fossil fuel combustion as major emission source. In contrast, the high δ15N (16.1 ± 3.2‰) with enhanced TC/TN ratio reveals the impact of biomass burning in the air transported from the far eastern border region of China and Russia. Our findings highlight that the multi-isotopic composition is a useful tool to identify emission sources and to trace regional sources of carbonaceous and nitrogen aerosols.

The Korea–United States Air Quality (KORUS-AQ) field study was conducted during May–June 2016. The effort was jointly sponsored by the National Institute of Environmental Research of South Korea and the National Aeronautics and Space Administration of the United States. KORUS-AQ offered an unprecedented, multi-perspective view of air quality conditions in South Korea by employing observations from three aircraft, an extensive ground-based network, and three ships along with an array of air quality forecast models. Information gathered during the study is contributing to an improved understanding of the factors controlling air quality in South Korea. The study also provided a valuable test bed for future air quality–observing strategies involving geostationary satellite instruments being launched by both countries to examine air quality throughout the day over Asia and North America. This article presents details on the KORUS-AQ observational assets, study execution, data products, and air quality conditions observed during the study. High-level findings from companion papers in this special issue are also summarized and discussed in relation to the factors controlling fine particle and ozone pollution, current emissions and source apportionment, and expectations for the role of satellite observations in the future. Resulting policy recommendations and advice regarding plans going forward are summarized. These results provide an important update to early feedback previously provided in a Rapid Science Synthesis Report produced for South Korean policy makers in 2017 and form the basis for the Final Science Synthesis Report delivered in 2020.

We present trace gas vertical profiles observed by instruments on the NASA DC-8 and at a ground site during the Korea-US air quality study (KORUS) field campaign in May to June 2016. We focus on the region near the Seoul metropolitan area and its surroundings where both anthropogenic and natural emission sources play an important role in local photochemistry. Integrating ground and airborne observations is the major research goal of many atmospheric chemistry field campaigns. Although airborne platforms typically aim to sample from near surface to the free troposphere, it is difficult to fly very close to the surface especially in environments with complex terrain or a populated area. A detailed analysis integrating ground and airborne observations associated with specific concentration footprints indicates that reactive trace gases are quickly oxidized below an altitude of 700 m. The total OH reactivity profile has a rapid decay in the lower part of troposphere from surface to the lowest altitude (700 m) sampled by the NASA DC-8. The decay rate is close to that of very reactive biogenic volatile organic compounds such as monoterpenes. Therefore, we argue that photochemical processes in the bottom of the boundary layer, below the typical altitude of aircraft sampling, should be thoroughly investigated to properly assess ozone and secondary aerosol formation.

Ketene, a rarely measured reactive VOC, was quantified in the emission plumes from Daesan petrochemical facility in South Korea using airborne PTR-TOF-MS measurements. Ketene mixing ratios as high as ~ 40–50 ppb were observed in the emission plumes. Emission rates of ketene from the facility were estimated using a horizontal advective flux approach and ranged from 84–316 kg h−1. These emission rates were compared to the emission rates of major VOCs such as benzene, toluene, and acetaldehyde. Significant correlations (r2 > 0.7) of ketene with methanol, acetaldehyde, benzene, and toluene were observed for the peak emissions, indicating commonality of emission sources. The calculated average ketene OH reactivity for the emission plumes over Daesan ranged from 3.33–7.75 s−1, indicating the importance of the quantification of ketene to address missing OH reactivity in the polluted environment. The calculated average O3 production potential for ketene ranged from 2.98–6.91 ppb h−1. Our study suggests that ketene has the potential to significantly influence local photochemistry and therefore, further studies focusing on the photooxidation and atmospheric fate of ketene through chamber studies is required to improve our current understanding of VOC OH reactivity and hence, tropospheric O3 production.

A new method for the concurrent treatment of Cr(VI)-contaminated wastewater and production of the useful I2 chemical was developed. The method is based on the redox reaction between Cr(VI) and I– t...

We report OH reactivity observations by a chemical ionization mass spectrometer – comparative reactivity method (CIMS-CRM) instrument in a suburban forest of the Seoul Metropolitan Area (SMA) during Korea US Air Quality Study (KORUS-AQ 2016) from mid-May to mid-June of 2016. A comprehensive observational suite was deployed to quantify reactive trace gases inside of the forest canopy including a high-resolution proton transfer reaction time of flight mass spectrometer (PTR-ToF-MS). An average OH reactivity of 30.7 ± 5.1 s−1 was observed, while the OH reactivity calculated from CO, NO + NO2 (NOx), ozone (O3), sulfur dioxide (SO2), and 14 volatile organic compounds (VOCs) was 11.8 ± 1.0 s−1. An analysis of 346 peaks from the PTR-ToF-MS accounted for an additional 6.0 ± 2.2 s−1 of the total measured OH reactivity, leaving 42.0 % missing OH reactivity. The missing OH reactivity most likely comes from VOC oxidation products of both biogenic and anthropogenic origin.

In this presentation, we will discuss the top down emission estimates of SO2 and volatile organic compounds using mass spectrometers integrated on a research aircraft with a fast-meteorological sensor. The study area is four coal power plants, one steel mill, and one petrochemical industrial facility, located in the Tae-ahn Peninsular in South Korea 50 km away from the southern tip of the Seoul Metropolitan Area. We conducted 20 research flights to closely monitor emissions from each facility. We will present detailed analysis of instantaneous emission rates to verify emission inventories to proceed their impacts to regional air quality, particularly towards the Seoul Metropolitan Area with a population of 25 millions, using a semi-Lagrangian photochemical box model.

Nitryl chloride (ClNO2) plays an important role as a night-time reservoir of NOX and the source of Cl radical during the daytime, which consequently affects the ozone photochemistry. Its impacts on regional air quality in East Asia, however, are not fully understood so far. We here use extensive observations during the international KORea-US cooperative Air Quality field study in Korea (KORUS-AQ), which occurred in May-June 2016, with a 3-D chemistry transport model to examine the impacts of ClNO2 chemistry on radical species and total nitrate concentrations in East Asia. We first update the model by implementing chlorine chemistry and latest anthropogenic chlorine emissions of China and South Korea. We conduct model simulations for May-June, 2016 and validate the model by comparing against the observations from the KORUS-AQ campaign. We find that the ClNO2 chemistry in the model results in an increase of ozone by ~1.4 ppbv (~2.5%), Cl radical by ~ 4.6x103 molec cm-3 (~3600%), OH ~8.2x104 molec cm-3 (~5.3%), HO2 ~6.6 molec cm-3 (~3.0%), a decrease of TNO3 (HNO3 + nitrate aerosol) concentrations by ~2 μg m-3 on a daily mean basis during the campaign. Overall, the enhanced conversion of NO to NO2 driven by ClNO2 chemistry contributes to higher oxidant concentrations in the model. As a result, the updated model shows a better agreement with the observations in Korea during the KORUS-AQ campaign.

The Arctic is rapidly transforming due to sea ice loss, increasing shipping activity, and oil and gas development. Associated marine and combustion emissions influence atmospheric aerosol composition, impacting complex aerosol–cloud–climate feedbacks. To improve understanding of the sources and processes determining Arctic aerosol composition, atmospheric particles were collected aboard the Korean icebreaker R/V Araon cruising within the Bering Strait and Chukchi Sea during August 2016. Offline analyses of individual particles by microspectroscopic techniques, including scanning electron microscopy with energy dispersive X-ray spectroscopy and atomic force microscopy with infrared spectroscopy, provided information on particle size, morphology, and chemical composition. The most commonly observed particle types were sea spray aerosol (SSA), comprising ∼60–90%, by number, of supermicron particles, and organic aerosol (OA), comprising ∼50–90%, by number, of submicron particles. Sulfate and nitrate were internally mixed within both SSA and OA particles, consistent with particle multiphase reactions during atmospheric transport. Within the Bering Strait, SSA and OA particles were more aged, with greater number fractions of particles containing sulfate and/or nitrate, compared to particles collected over the Chukchi Sea. This is indicative of greater pollution influence within the Bering Strait from coastal and inland sources, while the Chukchi Sea is primarily influenced by marine sources.

Peroxyacetyl nitrate (PAN) is produced by photochemical oxidation reactions with abundant NOx and volatile organic compounds (VOCs); therefore, it is considered as a photochemical pollution indicator. In this study, PAN, O3, and their precursors were measured at three heights (5.4, 23, and 40.5 m) on a 41-m tower in Taehwa Research Forest (TRF) near the Seoul Metropolitan Area (SMA) from August 25 to September 9, 2011. The PAN was determined every 2 minutes using gas chromatography with luminol chemiluminescence detection (GC-LCD). All reactive gases were measured for 15 minutes at each height. The mean and maximum PAN concentrations were 0.3 and 3.1 ppbv, respectively. The mean and maximum O3 concentrations were 13.1 and 79.8 ppbv, respectively. The average NOx concentration was 6.57 ppbv. At the TRF, PAN and O3 concentrations were well correlated (r = 0.8) and greatly elevated when the air mass was affected by urban outflows from the SMA, which was clearly demonstrated by an increase in NO2. These high NO2 concentrations were observed along with a shift in wind direction at 17:00 (KST) and resulted in the maximum observed values of PAN and O3 in the present study. In addition, the concentration enhancement was more pronounced for PAN and at heights above the canopy. These results highlight PAN as a robust tracer indicating urban impacts at peri-urban forest sites.

Author(s): Kim, S; Jeong, D; Sanchez, D; Wang, M; Seco, R; Blake, D; Meinardi, S; Barletta, B; Hughes, S; Jung, J; Kim, D; Lee, G; Lee, M; Ahn, J; Lee, SD; Cho, G; Sung, MY; Lee, YH; Park, R | Abstract: We present the ambient ozone and relevant observed trace gas dataset in Seoul, South Korea, during the Megacity Air Pollution Studies (MAPS)-Seoul field campaign from May to June of 2015 (MAPS-Seoul 2015). We observed two distinctive periods, one with higher and the other with lower daytime ozone levels despite mostly clear conditions for both periods. The importance of peroxy radical contributions to excess ozone production is illustrated by the substantial differences in the Leighton constant (Φ) for the two periods. Moreover, higher levels of hydroxyl radical (OH) reactivity (s–1) were observed during the high ozone episode compared to the low ozone episode by as much as ~5 s–1. The contributions of nitrogen oxides (NOx) to OH reactivity become less important than those of volatile organic compounds (VOCs) during the high ozone episode, which suggests the NOx saturated ozone production regime. It was also notable that the biogenic VOC isoprene consistently contributed the most to OH reactivity from among the observed VOCs during the afternoon throughout the whole field campaign. Finally, we ran multiple box model scenarios to evaluate the ozone production rates of three different air mixtures: a high ozone mixture, a low ozone mixture, and a simulation of the regional air quality. The results indicate that the total OH reactivity levels and the relative contributions of VOCs to NOx play critical roles in ozone production rates. The simulated air quality mixture results in lower OH reactivity, causing lower ozone production rates than those calculated for the high ozone mixture, which clearly indicates the need for further improvements in the regional model to accurately simulate ozone precursors in the region. The results of this study suggest that a comprehensive trace gas dataset combined with observations of the OH reactivity enables us to properly diagnose the photochemistry behind ozone pollution, leading to effective ozone abatement policies.

Author(s): Kim, H; Choi, WC; Rhee, HJ; Suh, I; Lee, M; Blake, DR; Kim, S; Jung, J; Lee, G; Kim, DS; Park, SM; Ahn, J; Lee, SD | Abstract: To understand the chemical mechanisms of controlling factors in ozone (O3) formation in early summer in Seoul, a comprehensive study encompassing measurement and modeling was conducted under the Megacity Air Pollution Study-Seoul (MAPS-Seoul) campaign. From May 18 to June 12, 2015, O3 and peroxyacetyl nitrate (PAN) were measured, along with their precursors, including NOx and volatile organic compounds (VOCs), at the Korea Institute of Science and Technology, located in northeast Seoul. VOCs were sampled in a canister twice a day (at 09:30 and 15:00) and analyzed via gas chromatography. The meteorological conditions and chemical regimes of the air masses were clearly distinguished during the study period. In May, NOx concentrations were higher with more pronounced diurnal cycles of precursors and O3 under constant westerly winds. By contrast, stagnant conditions developed in June, which reduced the inflow of primary emissions from the downtown area but increased the influence from the neighboring forest under high temperatures. As a result, the ratio of O3 to odd oxygen was higher in June, indicating a less efficient removal of O3 by NOx. In the same context, the air mass was chemically more aged with a higher NO2/NOx ratio and enhanced OH reactivity of oxygenated and biogenic VOCs in June. The overall measurement results suggest that O3 formation is slightly more sensitive to VOCs than to NOx in Seoul during this season, when O3 concentrations are the highest of the year.

Isoprene plays a critical role in air quality and climate. Photosynthesis (gross primary productivity, GPP) and formaldehyde (HCHO) are both related to isoprene emission at large spatiotemporal scales, but neither is a perfect proxy. We apply multiple satellite products and site-level measurements to examine the impact of water deficit on the three interlinked variables at the Missouri Ozarks site during a 20-day mild dryness stress in summer 2011 and a 3-month severe drought in summer 2012. Isoprene emission shows opposite responses to the short- and long-term droughts, while GPP was substantially reduced in both cases. In 2012, both remote-sensed solar-induced fluorescence (SIF) and satellite HCHO column qualitatively capture reductions in flux-derived GPP and isoprene emission, respectively, on weekly to monthly time scales, but with muted responses. For instance, as flux-derived GPP approaches zero in late summer 2012, SIF drops by 29–33% (July) and 19–27% (August) relative to year 2011. A possible explanation is that electron transport and photosystem activity are maintained to a certain extent under the drought stress. Similarly, flux tower isoprene emissions in July 2012 are 54% lower than July 2011, while the relative reductions in July for 3 independent satellite-derived HCHO data products are 27%, 12% and 6%, respectively. We attribute the muted HCHO response to a photochemical feedback whereby reduced isoprene emission increases the oxidation capacity available to generate HCHO from other volatile organic compound sources. Satellite SIF offers a potential alternative indirect method to monitor isoprene variability at large spatiotemporal scales from space, although further research is needed under different environmental conditions and regions. Our analysis indicates that fairly moderate reductions in satellite SIF and HCHO column may imply severe drought conditions at the surface.

One of the least understood aspects in atmospheric chemistry is how urban emissions influence the formation of natural organic aerosols, which affect Earth’s energy budget. The Amazon rainforest, during its wet season, is one of the few remaining places on Earth where atmospheric chemistry transitions between preindustrial and urban-influenced conditions. Here, we integrate insights from several laboratory measurements and simulate the formation of secondary organic aerosols (SOA) in the Amazon using a high-resolution chemical transport model. Simulations show that emissions of nitrogen-oxides from Manaus, a city of ~2 million people, greatly enhance production of biogenic SOA by 60–200% on average with peak enhancements of 400%, through the increased oxidation of gas-phase organic carbon emitted by the forests. Simulated enhancements agree with aircraft measurements, and are much larger than those reported over other locations. The implication is that increasing anthropogenic emissions in the future might substantially enhance biogenic SOA in pristine locations like the Amazon., It remains unclear how urban emissions influence the formation of secondary organic aerosols (SOA), including in the Amazon forest. Here, the authors simulate the formation of SOAs in the Amazon using a high-resolution regional chemical transport model. They find that urban emissions of NOx from Manaus enhance the production of biogenic SOA by 60–200%.

To estimate dry deposition flux of atmospheric water-soluble nitrogen (N), including ammonium (NH4+), nitrate (NO3&minus, ), and water-soluble organic nitrogen (WSON), aerosol samples were collected over the subarctic western North Pacific Ocean in the summer of 2016 aboard the Korean icebreaker IBR/V Araon. During the cruise, concentrations of NH4+, NO3&minus, and WSON in bulk (fine + coarse) aerosols ranged from 0.768 to 25.3, 0.199 to 5.94, and 0.116 to 14.7 nmol m&minus, 3, respectively. Contributions of NH4+, NO3&minus, and WSON to total water-soluble N represented ~74%, ~17%, and ~9%, respectively. Water-soluble N concentrations showed a strong gradient from the East Asian continent to the subarctic western North Pacific Ocean, indicating that water-soluble N species were mainly derived from anthropogenic or terrestrial sources. During sea fog events, coarse mode NO3&minus, was likely to be scavenged more efficiently by fog droplets than fine mode NO3&minus, besides, WSON was detected only in fine mode, suggesting that there may have been a significant influence of sea fog on WSON, such as the photochemical conversion of WSON into inorganic N. Mean dry deposition flux for water-soluble total N (6.3 &plusmn, 9.4 &micro, mol m&minus, 2 d&minus, 1) over the subarctic western North Pacific Ocean was estimated to support a minimum carbon uptake of 42 &plusmn, 62 &micro, mol C m&minus, 2d&minus, 1 by using the Redfield C/N ratio of 6.625.

Developing a cost-effective method for the separation and recovery of nanomaterials for water treatment is challenging due to the significantly high recovery cost associated with nanomaterial-based water treatment processes. In this study, we synthesized magnetically separable iron oxide/tungsten oxide (Fe2O3/WO3) composites through a chemical co-precipitation method and employed them as peroxymonosulfate (PMS) activators for the degradation of organic pollutants under visible light. Electron spin resonance analysis, chemical quenching, and photoluminescence analysis suggested that hydroxyl radicals, sulfate radicals, and valence band holes contribute to the degradation processes in the Fe2O3/WO3/PMS system under visible light. The results of the degradation and recovery experiments based on the mass ratio of WO3 to Fe2O3 ([WO3]:[Fe2O3]) in the Fe2O3/WO3 composite indicated that the Fe2O3/WO3 composite with [WO3]:[Fe2O3] = 2:1, which can be completely recovered using a magnet (magnetic flux density = 2500 G), is the optimal photocatalyst for PMS activation. The effects of reaction parameters, such as the PMS concentration, Fe2O3/WO3 dosage, solution pH, and background anions (chloride, carbonate, nitrate, and phosphate)/humic acid, on the degradation kinetics were investigated and discussed. Under visible light irradiation, the Fe2O3/WO3/PMS system efficiently degraded various organic pollutants, including 4-chlorophenol, 2-chlorophenol, 4-bromophenol, 4-methylphenol, 2,4-dimethylphenol, bisphenol A, tryptophan, sulfamethoxazole, sulfisoxazole, and furfuryl alcohol. In addition, the complete degradation of 4-chlorophenol in the Fe2O3/WO3/PMS system under visible light was achieved for up to five degradation cycles when Fe2O3/WO3 was reused after recovery using a magnet.

A new method for the activation of peroxymonosulfate (PMS) using ferric ions (Fe3+) and visible light (λ > 420 nm) was developed and investigated as a water treatment method for the degradation of various organic pollutants. Complete degradation of 100 μM of 4-chlorophenol (4-CP) was achieved after 60 min in the presence of PMS (1 mM) and Fe3+ (1 mM) under visible-light irradiation. However, the degradation of 4-CP was negligible or minor in the absence of either PMS, Fe3+, or visible-light irradiation. The visible-light absorption of Fe3+ was enhanced through complexation with PMS (HSO5−−Fe(OH)2+), although PMS itself does not absorb visible light. Inner-sphere electron transfer in the HSO5−−Fe(OH)2+ complex under visible light generated sulfate (SO4 −) and hydroxyl radicals ( OH). The production of SO4 − and OH in the PMS/Fe3+/visible light system was verified by electron paramagnetic resonance (EPR) spectroscopy and fluorescence spectroscopy. The degradation of 4-CP was significantly reduced with isopropyl alcohol (as a scavenger for both OH and SO4 −), but only slightly reduced with tert-butyl alcohol (as a OH scavenger). This behavior suggests that SO4 − acts as a primary oxidant in the PMS/Fe3+/visible light system. The PMS/Fe3+/visible light system efficiently degraded a wide spectrum of organic pollutants (e.g., 4-CP, bisphenol A, 2,4-dimethylphenol, furfuryl alcohol, sulfamethoxazole, tryptophan, and sulfanilamide). In addition, the degradation efficiency of the PMS/Fe3+/visible light system remained constant over multiple cycles with the intermittent addition of PMS only.

This study presents a freezing method for accelerating the peroxymonosulfate (PMS)-mediated degradation process. The degradation of furfuryl alcohol (FFA) in the presence of PMS was markedly accelerated by freezing. The degradation efficiency of FFA was only 10.4% in aqueous solution at 25 °C, but 100% degradation was achieved in frozen solution at −20 °C after 3 h of reaction at [FFA] = 20 µM and [PMS] = 100 µM. This accelerated PMS-mediated degradation of FFA in the frozen solution is due to the concentration of both PMS and FFA in ice grain boundaries, which increases the collision frequency between PMS and FFA thereby facilitating redox transformation. The mapping images of PMS and FFA in the frozen sample obtained using confocal Raman microscopy provide clear evidence of the accumulation of PMS and FFA in the ice grain boundaries after freezing. The experimental results with sulfate radical (SO4 −) scavengers, no production of hydroxyl radicals ( OH) and SO4 −, and the highly pollutant-dependent degradation efficiency suggest that the PMS-mediated degradation in frozen solution primarily proceeds through the direct electron transfer from organic pollutants to PMS (non-radical mechanism) rather than the reaction of SO4 − or OH with organic pollutants (radical mechanism). The degradation efficiency of the PMS/freezing system was similar across the pH range of 3–10. In addition, the PMS/freezing system worked efficiently in the temperature range of −10 to −35 °C. This result implies that the PMS/freezing system can be operated without external energy in cold regions.

During the May-June 2016 International Cooperative Air Quality Field Study in Korea (KORUS-AQ), light synoptic meteorological forcing facilitated Seoul metropolitan pollution outflow to reach the remote Taehwa Research Forest (TRF) site and cause regulatory exceedances on 24 days. Two of these severe pollution events are thoroughly examined. The first, occurring on 17 May 2016, tracks transboundary pollution transport exiting eastern China and the Yello Sea, traversing the Seoul Metropolitan Area (SMA), and then reaching TRF in the afternoon hours with severely polluted conditions. This case study indicates that although outflow from China and the Yellow Sea were elevated with respect to chemically unperturbed conditions, the regulatory exceedance at TRF was directly linked in time, space, and altitude to urban Seoul emissions. The second case studied, occurring on 09 June 2016, reveals that increased levels of biogenic emissions, in combination with amplified urban emissions, were associated with severe levels of pollutions and a regulatory exceedance at TRF. The case studies are assessed with multiple aircraft, model (photochemical and meteorological) simulations, in-situ chemical sampling, and extensive ground-based profiling at TRF. These observations clearly identify TRF and the surrounding rural communities as receptor sites for severe pollution events associated with Seoul outflow, which will result in long-term negative effects to both human health and agriculture in the affected areas.

Biogenic isoprene emissions play a very important role in atmospheric chemistry. These emissions are strongly dependent on various environmental conditions, such as temperature, solar radiation, plant water stress, ambient ozone and CO2 concentrations, and soil moisture. Current biogenic emission models (i.e., Model of Emissions of Gases and Aerosols from Nature, MEGAN) can simulate emission responses to some of the major driving variables, such as short-term variations in temperature and solar radiation, but the other factors are either missing or poorly represented. In this paper, we propose a new modelling approach that considers the physiological effects of drought stress on plant photosynthesis and isoprene emissions for use in the MEGAN3 biogenic emission model. We test the MEGAN3 approach by integrating the algorithm into the existing MEGAN2.1 biogenic emission model framework embedded into the global Community Land Model of the Community Earth System Model (CLM4.5/CESM1.2). Single-point simulations are compared against available field measurements at the Missouri Ozarks AmeriFlux (MOFLUX) field site. The modelling results show that the MEGAN3 approach of using of a photosynthesis parameter (Vcmax) and soil wetness factor (βt) to determine the drought activity factor leads to better simulated isoprene emissions in non-drought and drought periods. The global simulation with the MEGAN3 approach predicts a 17% reduction in global annual isoprene emissions, in comparison to the value predicted using the default CLM4.5/MEGAN2.1 without any drought effect. This reduction leads to changes in surface ozone and oxidants in the areas where the reduction of isoprene emissions is observed. Based on the results presented in this study, we conclude that it is important to simulate the drought-induced response of biogenic isoprene emission accurately in the coupled Earth System model.