Ozone (O3), a short-lived climate pollutant, continues to increase despite policies aimed at suppressing its precursors in South Korea. The government operates approximately 500 observatories to monitor O3 and trace gases. Researchers use these data to address the ongoing issue of increasing O3 levels. However, challenges in data retrieval from observatories may introduce biases in O3 studies. In this study, we developed a graph-based machine learning model to simulate missing O3 concentrations for mitigate bias. The model incorporates spatiotemporal distribution characteristics using a merged observation dataset from South Korea in 2021. Regardless of region or length of missing data, the model effectively simulates O3 variations with R2 of up to 0.9 and RMSE of 3.6. To determine the influence of input parameters on O3 interpolation, we used eXplainable AI methods. The results indicated that NO2 is the most important factor in cities, while photochemical indicators are more influential in provinces.

A series of experiments was conducted to characterize a medium-sized 27-m3 smog chamber, KIST atmospheric processes simulation chamber (K-CAPS) in terms of the gas and particle wall losses, spectrum of light sources, and background reactivity and evaluate its suitability for simulating atmospheric reactions. Photo-oxidation experiments using a toluene and NOx mixture were then carried out to investigate the effects of the UV lamp type, UV intensity, and ammonium sulfate seeds on the formation of secondary organic aerosols (SOA) and O3, and on the physicochemical properties of SOA including hygroscopicity. When UVA and UVB lamps were used together, formation of SOA and O3 was faster than that for UVA lamps alone. And higher UV intensity also resulted in faster formation of SOA and O3, but the increase in O3 with accumulated OH exposure and the increase in SOA with reacted toluene concentrations are consistent regardless of photolysis rate of NO2 implying that increment in UV intensity can be acceptable to shorten the experiment time for relatively long aging processes such as multiday reactions. More SOA and less O3 were formed when ammonium sulfate seeds were initially injected and average RH was relatively higher, compared to the dry experiment without seeds. These results must be useful to understand the physicochemical properties of SOA formed through photo-oxidation of anthropogenic VOCs in real-world atmospheric conditions.

For a comprehensive evaluation of the key factors determining the oxidative potential (OP) of PM2.5, 75 samples of PM2.5 were collected in urban Seoul, South Korea, during 2019-2021, and dithiothreitol consumption (DTTv) was measured using a DTT assay, coupled with an analysis of major constituents and stable isotope ratios of PM2.5. For the entire sample set, the mean DTTv value was 0.58 ± 0.48 nmol m-3 min-1 for PM2.5 of 29.1 ± 12.2. DTTv exhibited a general dependence on of PM2.5 concentrations and major constituents, including NO4+, SO42-, NH4+, and organic carbon (OC). Specifically, NO3- and NH4+ demonstrated the most robust correlation with DTTv during the cold season, whereas only elemental carbon (EC) showed a significant correlation with DTTv in the warm season. The δ13C of total carbon (TC) and δ15N of total nitrogen (TN) displayed an inverse correlation concerning DTT activities, suggesting the significant contribution from solid fossil fuels and biomass burning to the oxidative potential of PM2.5, particularly during the cold season when PM2.5 was notably high. In contrast, vehicle emissions were found to influence DTTv even at low PM2.5 levels in warm seasons. This study provides insights into the intricate dynamics influencing the oxidative potential of PM2.5.

The high level of ozone throughout the troposphere is an emerging concern for East Asia and Southeast Asia. Here, we analyze available surface ozone measurements from the past two decades (2005-2021) over eight countries, with 10 ozonesonde and aircraft measurements within this region. At the surface, the seasonal mean ozone over 2017-2021 varies from 30 nmol mol-1 (i.e., 30 ppb) in Southeast Asia to 75 nmol mol-1 in summer in northern China. The metric of seasonal 95th percentile ozone can identify the multiple hot spots of ozone pollution of over 85 nmol mol-1 in Southeast Asia. The new World Health Organization (WHO) peak-season ozone standard indicates that both East Asia and Southeast Asia face a widespread risk of long-term exposure. The surface ozone increase in South Korea and Southeast Asia from 2005 was leveling off or even decreasing in the past decade, while the ozone increase in the 2000s over China has amplified since 2013. Surface ozone trends in Japan and Mongolia were flat in the past decade. In the troposphere, the available measurements show an overall increasing tendency at different altitudes from a three-decade perspective, although the trend in the past decade remains unclear due to data availability. The difference in the tropospheric ozone level between East Asia and Southeast Asia is likely due to the high background ozone from the stratospheric intrusion over Northeast Asia. In terms of ozone controls, our results suggest that anthropogenic emissions determine the occurrence of high ozone levels, but the underappreciated strong ozone climate penalty, particularly over Southeast Asia, will make ozone controls harder under a warmer climate.

This study examined the seasonal variations and influencing factors for black carbon (BC) concentrations and aerosol optical depth (AOD) at the Socheongcho Ocean Research Station (SORS) on the Korean Peninsula from July 2019 to December 2020. An AOD algorithm was developed and validated using the Geo-KOMPSAT-2A (GK-2A) satellite. The GK-2A AOD demonstrated comparable performance to that of Low Earth Orbit satellites, including the Terra/MODIS (R2 = 0.86), Aqua/MODIS (R2 = 0.83), and AERONET AODs (R2 = 0.85). Multi-angle absorption photometry revealed that seasonal average BC concentrations were the highest in winter (0.91 ± 0.80 µg·m−3), followed by fall (0.80 ± 0.66 µg·m−3), wet summer (0.75 ± 0.55 µg·m−3), and dry summer (0.52 ± 0.20 µg·m−3). The seasonal average GK-2A AOD was higher in wet summer (0.45 ± 0.37 µg·m−3) than in winter. The effects of meteorological parameters, AERONET AOD wavelength, and gaseous substances on GK-2A AOD and BC were investigated. The SHapley Additive exPlanations-based feature importance analysis for GK-2A AOD identified temperature, relative humidity (RH), and evaporation as major contributors. BC concentrations were increased, along with PM2.5 and CO levels, due to the effects of combustion processes during fall and winter. Analysis of high-aerosol-loading cases revealed an increase in the fine-mode fraction, emphasizing the meteorological effects on GK-2A AOD. Thus, long-range transport and local BC sources played a critical role at the SORS.

Air pollution in Chiang Mai during the dry winter season is extremely severe. During this period, high levels of fine particles are primarily generated by open biomass burning in Thailand and neighboring countries. In this study, ambient VOC(Volatile Organic Compounds) samples were collected using an adsorbent tube from 13 March to 26 March 2024, with careful consideration of sampling uncertainties to ensure data reliability. Furthermore, while interannual variability exists, the findings reflect atmospheric conditions during this specific period, allowing for an in-depth VOC assessment. A comprehensive approach to VOCs was undertaken, including benzene, toluene, ethylbenzene, m,p-xylene (BTEX); biogenic volatile organic compounds (BVOCs); and carbonyl compounds. Regression analysis was performed to analyze the correlation between isoprene concentrations and wind direction. The results showed a significant variation in isoprene levels, indicating their high concentrations due to biomass burning originating from northern areas of Chiang Mai. The emission sources of BTEX and carbonyl compounds were inferred through their ratio analysis. Additionally, correlation analyses between PM2.5, BTEX, and carbonyl compounds were conducted to identify common emission pathways. The ratio of BTEX among compounds suggested that long-range pollutant transport contributed more significantly than local traffic emissions. Carbonyl compounds were higher during the episode period, which was likely due to local photochemical reactions and biological contributions. Previous studies in Chiang Mai have primarily focused on PM2.5, whereas this study examined individual VOC species, their temporal trends, and their interrelationships to identify emission sources.

Abstract. Studying tropospheric ozone over the remote areas of the planet, such as the open oceans and the polar regions, is crucial to understand the role of ozone as a global climate forcer and regulator of atmospheric oxidative capacity. A focus on the pristine oceanic and polar regions complements the available land-based data sets and provides insights into key photochemical and depositional loss processes that control the concentrations, spatio-temporal variability of ozone, and the physico-chemical mechanisms driving these patterns. However, an assessment of the role of ozone over the oceanic and polar regions has been hampered by a lack of comprehensive observational data sets. Here, we present the first comprehensive collection of ozone data over the oceans and the polar regions. The overall data set consists of 77 ship cruises/buoy-based observations and 48 aircraft-based campaigns. The data set, consisting of more than 630,000 independent ozone measurement data points covering the period from 1977 to 2022 and an altitude range from the surface to 5000 m (with a focus on the lowest 2000 m), allows systematic analyses of the spatio-temporal distribution and long-term trends over the defined 11 ocean/polar regions. The data sets from ships, buoys, and aircrafts are complemented with an ozonesonde data set from 29 launch sites or field campaigns, and by 21 non-polar and 17 polar ground-based stations data sets. The data were filtered by using backward trajectories calculated with the HYSPLIT model from the individual observation points to extract essentially oceanic observations, defined as air masses that have travelled over oceans for 72 hours or more, which were further tested with the coincident Radon observations. The oceanic and polar data thus selected showed typically flat diurnal patterns at high latitudes and daytime decreases (11–16 %) at low latitudes, indicating the adequacy of the data collection and processing procedures, as well as the potential for further studies of processes with statistical robustness and coverage. The ship/buoy- and aircraft-based data sets presented here will supplement the land-based ones in the TOAR-II database to provide a fully global assessment of tropospheric ozone.

Significant PM2.5 pollution has been prevalent on a regional scale in East Asia including a megacity Seoul in South Korea. Here, we explore fine-aerosol episodes occurred in Seoul during the Satellite Integrated Joint monitoring of Air Quality (SIJAQ) campaign from October to November of the 2021, focusing on experimental evidences of heterogeneous reactions to form secondary aerosol under a highly oxidized atmospheric condition. At this urban site in Seoul, vehicle exhaust was the clear source of fresh emissions, leading to a high level of NO and small refractory black carbon (rBC) particles (mass median diameter of 162 nm +/- 16 nm) in the morning time. The hourly mass concentration of PM2.5 ranged from 5.3 mu g m(-3) to 146.1 mu g m(-3), averaging at 24.5 +/- 22.2 mu g m(-3). During the campaign, the most intense episode, EP3 (November 18-21), recorded an average PM2.5 concentration of 72.5 +/- 38.2 mu g m(-3), peaking at 146.1 mu g m(-3), was characterized by relatively higher temperature (similar to 12 degrees C) and relative humidity (67 %) on average thoroughly governed by continental migratory high and westerly winds. While the average NO3- concentration was 27.7 mu g m(-3), four times the whole campaign's average, EP3 was highlighted by a high morning NO2/NOx ratio and significantly elevated daytime and nighttime O-x (O-3+NO2) concentrations compared to non-episode days. Throughout the entire campaign, NOz surrogate (NO2(CL)-NO2(CAPS)), O-x, and Fmoderate + thick (the combined number fractions of moderately and thickly coated-rBC particles) tended to increase with the PM2.5 concentration. During the daytime, as PM2.5 increased, Fmoderate + thick showed a monotonic increase, accompanied by RH rising from 54 +/- 16% to 63 +/- 11%. In contrast, at nighttime of humid condition with RH often exceeding 70% the enhancement of Fmoderate + thick was more sensitive to condensable gas levels than RH. Given that high levels of PM2.5 (>60 mu g m(-3)) were observed only during EP3, enhanced levels of NOz surrogate, O-x, F-moderate + thick,F- and RH were evident characteristics of EP3. Such chemical and meteorological conditions suggest that the chemically enhanced oxidation state was evident during EP3, which promoted the formation of secondary aerosols on primary particles including rBC, especially under conditions of elevated RH. Considering the recent trend of increasing number of vehicles and rising atmospheric O-3 concentrations in East Asia, future studies should be well designed to investigate the detailed mechanisms involved in heterogeneous reactions that lead to the formation of secondary aerosols.

Odor is becoming one of the serious environmental issues as the industry develops. Electron beam technology has recently attracted attention as an AOP (Advanced Oxidation Process) for air purification, water treatment, and soil remediation. This work studied the removal of major livestock odor such as ammonia (NH3), hydrogen sulfide (H2S), and methanethiol (CH3SH) using a continuous gas flow electron beam treatment process. The effects of initial odor gas concentration, type of background gas, absorbed dose of the electron beam, voltage of the electron accelerator, and odor gas flow rate on the removal of odor gas were all studied in this continuous gas flow treatment system. As the absorbed dose of electron beam was increased, the removal efficiencies of odor gases NH3, H2S, and CH3SH all increased gradually. As the initial concentration of odor gas was decreased and as the flow rate of odor gas was increased, the removal efficiencies also increased. Regarding background gas, the odor gas removal efficiency was found to be in descending order of O2 > air > N2. The lower the voltage (MeV) of the electron beam, the higher the odor gas removal efficiency. This was attributed to the fact that, to set the same absorbed dose (kGy), as the voltage decreases, the current value (mA) increases. For the byproducts, as the absorbed dose of electron beam was increased, the concentration of byproducts increased. Regarding the gas-phase continuous electron beam treatment reactions, the optimal operating conditions must be derived by considering various operational variables, including the initial concentration, electron beam dose, background gas type, gas flow rate, and electron beam voltage. The results of this study show that, among several possibly relevant variables in removing odor gases in the continuous flow electron beam irradiation process, the current value can be considered one of the most important variables, along with the initial concentration and background gas.

Characteristics of atmospheric new particle formation (NPF) events were investigated using the data obtained from the ship measurement campaign named Yellow Sea Air Quality (YES-AQ) over the Yellow Sea during the springtime from 2019 to 2022. NPF events occurred 15 times for the valid 128 observation days for the four-year period, and the average and standard deviation formation rate (FR) and growth rate (GR) of the NPF events were 2.38 +/- 1.53 cm(-3) s(-1) and 4.11 +/- 2.81 nm h(-1), respectively. The FR and GR were close to those in urban regions, implying the unique characteristics of the Yellow Sea. Owing to the NPF events, the number concentrations of total aerosols and nucleation mode particles increased by approximately 7850 and 6002 cm(-3), respectively, and those of cloud condensation nuclei at 0.2% and 0.6% supersaturation increased by about 1269 and 3269 cm(-3), respectively. The NPF events mostly occurred under the meteorological conditions of low temperature and relative humidity as well as high solar radiation and wind speed. These meteorological conditions appeared predominantly when the air mass originated from the continent north of the Korean Peninsula. The current analyses based on the data measured repeatedly during a specific period each year, which were not well conducted in other maritime NPF studies, highlight the reliability of the presented characteristics of NPF events over the Yellow Sea.

Shortened multiday reaction experiments were conducted using the KIST chamber for atmospheric processes simulation (K-CAPS) to characterize the effects of ammonia (NH3) and relative humidity (RH) on the formation of secondary organic aerosols (SOA) due to photooxidation of a mixture of toluene and inorganic gases such as NOx, SO2, and NH3. UV lamps were repeatedly turned on for 3 h (daytime) and off for 6 h (nighttime), and precursors were injected to a reaction bag once (Multiday Initial injection, MI) or repeatedly (Multiday Cyclic injection, MC) to simulate high particulate matter episode due to foreign inflow episode and domestic stagnation episodes, respectively. As a result, the amount of SOA formed in the humid (RH 80 %) MI experiments with ammonia was approximately 1.1 times more than in the traditional single day experiment and approximately 1.6 times more than in the MC experiment, implying that aging processes including nighttime effects without additional emission of precursors during transport can produce more SOA as reactions progressed further under the experimental conditions of this study. The higher the initial RH, the more SOA was formed, with a slope increasing approximately 1.2 μg/m3 per unit RH, and the shorter run time required for SOA to increase to 30 μg/m3 (twice the WHO PM10 standard), with a slope decreasing approximately 0.3 h per unit RH, implying that more humid condition caused during long-range transport across the oceans is one of the possible reasons of high secondary aerosol formation. The SOA formation was reduced by approximately 60 % in the absence of ammonia, suggesting that ammonia reduction is needed to decrease not only secondary inorganic aerosols but also SOA. These results are useful to understand the major reason of high pollution of particulate matters by episode cases in urban areas.

From October till November in 2010 and during March of 2011, when Chinese outflow events were frequently encountered, the chemical composition of submicron particles (PM1.0) was determined hourly using a particle-into-liquid sampler at the Gosan Climate Observatory. Three distinctive pollution plume types were identified: haze aerosols impacted by biomass combustion, nanoparticle bursts associated with outflow from Beijing, and saline soil particles from salt deposits. The highest PM1.0 concentration was observed in a fall haze event, under near-stagnant high-pressure synoptic conditions that were characterized by the lowest visibility (< 5 km) and the highest K+ and OC concentrations, indicating the influence of biomass combustion. When strong high-pressure systems develop in China, they efficiently export fresh urban emissions from Beijing to the study region, as distinguished by nanoparticle bursts of > 104 cm−3 with highly elevated SO2 levels, even during the night. When air masses move rapidly from northeastern China to Gosan under strong wind conditions, the Ca2+ concentration, along with that of Cl− and Na+, is enhanced in PM1.0, which is attributed to the influence of saline transport from dry lakes. The results of this study reveal compositional details and information on both number and mass concentration for different PM1.0 plumes from anthropogenic and natural sources, all of which are associated with different kinds of Chinese outflow events.

Over the past few years, peroxyacetyl nitrate (PAN) has drawn significant attention as a key indicator of photochemical pollution owing to its intimate relationship with ozone and associated health effects. This study presents measurements conducted at the Korea University campus in Seoul during the high-ozone seasons from 2018 to 2021. PAN concentration was measured using fast gas chromatography with luminol chemiluminescence detection (GC-LCD), alongside measurements of O-3, volatile organic compounds (VOCs), NO, NO2, and meteorological variables, including boundary layer height (BLH). The mean concentrations of PAN and O-3 over the years were 0.56 ppbv and 35 ppbv in 2018, 1.29 ppbv and 58 ppbv in 2019, 0.21 ppbv and 50 ppbv 2020, and 0.53 ppbv and 46 ppbv in 2021, respectively. The annual variation observed in Seoul is consistent with trends seen in major cities worldwide during the COVID19 pandemic, reflecting a substantial reduction in urban emissions. Notably, the mean concentration of NOx and VOCs decreased significantly by more than 50 % and 25%, respectively, from 2019 to 2021. At temperatures above 30 degrees C, PAN decomposition was accelerated, decoupling a consistent positive relationship between PAN and O-3 in 2020 and 2021. The results of a 0-D photochemical model (F0AM) calculation demonstrated that PAN formation primarily stems from anthropogenic VOCs, particularly > C2 alkenes. Elevated PAN concentrations during nighttime were attributed to boundary layer expansion and upper-air entrainment. Instances where PAN concentrations surged to at least 3 ppbv or higher in 2019 were attributed to biomass burning impacted air, as evidenced by concurrent elevations in K+ and OC in PM2.5, and O-3. This study underscores the complex interplay of factors influencing PAN and ozone enhancements under decreased precursor levels, with an emphasis on dynamic change in the boundary layer, and long-distance transport of non-fossil sources during agricultural burning seasons.

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, O-3 , 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 O-3 concentrations were 13.1 and 79.8 ppbv, respectively. The average NOx concentration was 6.57 ppbv. At the TRF, PAN and O-3 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 O-3 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.

To understand the chemical mechanisms of controlling factors in ozone (O-3) 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, O-3 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 O-3 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 O-3 to odd oxygen was higher in June, indicating a less efficient removal of O-3 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 O-3 formation is slightly more sensitive to VOCs than to NOx in Seoul during this season, when O-3 concentrations are the highest of the year.

We have conducted a quantitative analysis of volatile organic compounds (VOCs) in Seoul from September 2022 to June 2023, employing passive air samplers (PAS) at 25 sites and continuous monitoring at five photochemical assessment monitoring stations (PAMS). Comparing VOCs concentrations and compositions from PAS and PAMS during the same time periods, we found that most VOCs showed no significant difference (p-value >0.05) between the methods, except for olefins, which were overestimated by 24 % in passive sampling, confirming PAS as an effective tool for assessing the spatial distribution of VOCs species over large areas. Throughout Seoul, median values of total volatile organic compounds (TVOCs) concentrations collected with passive samplers remained stable with a standard deviation of 1.22 ppbv, typically ranging from 11 to 13 ppbv, except for an increase during winter in the southwestern regions of the city, where intense industrial and vehicular emissions are reported in the current Clean Air Policy Support System (CAPSS) emissions inventory. Positive matrix factorization (PMF) analysis using the passive data revealed general consistency in the spatial distribution of area and road emissions when compared with CAPSS emission inventory, although localized discrepancies were observed. In quantitative assessments of TVOCs comparing PAS observations with emission-based models, modeled values were within 1.5 times the interquartile range of observed PAS concentrations over Seoul. However, the lack of detection of emission hotspots in southeastern Seoul in the PAS data, coupled with the omission of photochemical loss in our dispersion-only models, indicates that the current CAPSS emission inventory may significantly underestimate actual ambient VOCs levels, especially in summer.

"Nowadays, because of the global air pollution issue caused by fine dust, fine dust collection and removal technologies are crucial for enhancing living environments and human health. This research proposes a new pilot-scale electrospray cyclone (ESC) designed for the collection of submicron dust particles. The experimental apparatuses comprised a cyclone dust collector and an insulating tank. Initially, laboratory-scale single-nozzle visualization tests were conducted to determine the droplets’ number and size under various operating conditions. Subsequently, based on the visualization research outcomes, modifications were made to a section of the existing industrial cyclone, which was combined with the ESC. Performance assessments of the pilot-scale ESC were conducted under diverse water flowrates and corona power conditions. The capture efficiencies for PM10, PM2.5, and PM1.0 were measured up to 98.2%, 95.4%, and 90.3%, respectively. Both the environmental and economic viabilities of the newly-proposed ESC in this study were evaluated based on three aspects: its capacitive particle collection efficiency; capital cost and operational power consumption. This evaluation method has been defined as the Levelized Cost of Precipitator (LCOP), and it is intended to assess the environmental and economic performance of dust collectors. In these results, the ESC indicates relatively high quality of the dust collectors on the environmental and economic aspects. The environmental effect evaluation is based on non-captured particle emission. Based on these indices, we assess that the ESC has one of the promising alternatives of commercial precipitators."