Recent changes of trans-boundary air pollution over the Yellow Sea: Implications for future air quality in South Korea

Characteristics of sub-micron aerosols in the Yellow Sea and its environmental implications

The Yellow Sea, characterized by an influx of both natural marine and anthropogenic pollutants, coupled with favorable photochemical conditions, serve as key sites for potential interactions between atmospheric gases and aerosols. A recent air monitoring campaign in the Yellow Sea revealed aerosol contributions from four sources, with the highest mass concentrations and dominance of NO3- (38.1 ± 0.37 %) during winds from China. Indications of potential secondary aerosol formation were observed through the presence of hydrolysis and oxidation products of nitrate and volatile organic compounds. Correlations between time series distributions of biomass burning organic aerosols and particle number counts (Dp 100-500 nm, R2 = 0.94) further suggest potential size growth through adsorption and scavenging processes. The results from this study provide observational evidence of a shift in atmospheric compositions from sulfate to nitrate, leading to an increased atmospheric nitrogen deposition in the Yellow Sea.

Back-trajectory analyses for evaluating the transboundary transport effect to the aerosol pollution in South Korea

This study performed a back-trajectory analysis to determine the influence of transboundary transport on the extent of aerosol pollution in South Korea, based on 5-year PM2.5 measurements (2015-2019) in five cities covering South Korea. A transboundary transport case was selected if a back trajectory passed over a dedicated region (BOX 1 and BOX 2) in the Yellow Sea. First, we found that the frequency of transboundary transport largely increases in the high pollution case, and this pattern is almost consistent for all months and all five cities, indicating the importance of investigating the horizontal direction of air mass movement associated with PM2.5, which has been discussed extensively in previous studies. In this study, we also examined the altitude change and straight moving distance (defined as travel distance) of back trajectories regarding the extent of local PM2.5. Consequently, we found that back trajectories in high aerosol pollution showed much lower altitudes and shorter travel differences, implying a significant contribution of surface emissions and stagnant air conditions to severe aerosol pollution. As a result, the local PM2.5 level was not significantly enhanced when the air mass passed over the Yellow Sea if transboundary transport occurred at high altitudes with rapid movement (i.e., high altitude and long travel distance back-trajectory). Based on these results, we suggest utilizing the combined information of the horizontal direction, altitude variation, and length of back trajectories to better evaluate transboundary transport.

Identifying the external N and Hg inputs to the estuary ecosystem based on the triple isotopic information (δ15NNO3, Δ17ONO3 and δ18ONO3)

The supply and sources of N and Hg in the Geum estuary of the western coast of Korea were evaluated. Triple isotope proxies (δ15NNO3, Δ17ONO3 and δ18ONO3) of NO3- combined with conservative mixing between river and ocean waters were used to improve isotope finger-printing methods. The N pool in the Geum estuary was primarily influenced by the Yellow Sea water, followed by riverine discharge (821 × 106 mol yr-1) and atmospheric deposition (51 × 106 mol yr-1). The influence of the river was found to be greater for Hg than that of the atmosphere. The triple isotope proxies revealed that the riverine and atmospheric inputs of N have been affected by septic wastes and fossil fuel burning, respectively. From the inner estuary towards offshore region, the influence of the river diminishes, thus increasing the relative impact of the atmosphere. Moreover, the isotope proxies showed a significant influence of N assimilation in February and nitrification in May.

High aerosol loading over the Bohai Sea: Long-term trend, potential sources, and impacts on surrounding cities

Air pollution over the oceans has received less attention compared to densely populated urban areas of continents. The Bohai Sea, a semi-enclosed sea in northern China, is surrounded by thirteen industrial cities that have experienced significant improvements in air quality over the past decade. However, the changes in air pollution over the Bohai Sea and its impacts on surrounding cities remain poorly understood. To address this, this study investigated the evolution of air pollution and its chemical composition in the Bohai Sea over four decades, utilizing satellite remote sensing data, reanalysis datasets, emissions inventories, and statistical modeling. Historically, the region has suffered from severe air pollution, resulting from a combination of continental emissions and marine inputs (e.g., sea salt, ports and maritime vessel activities). The aerosol optical depth (AOD) over the sea was higher than the mean levels observed in its surrounding coastal cities. Statistically, 45% of the air masses reaching the Bohai Sea are associated with natural sources (dust- and marine-rich), while the remainder carry anthropogenic pollutants from continental regions. With the exception of Cangzhou city, these coastal cities suffer from air pollutants originating from the Bohai Sea. Cities in the northern region of the sea, spanning from Tianjin to Yingkou, are particularly impacted. The majority of the surrounding cities are affected by a large proportion of anthropogenic aerosol types transported through air masses from the Bohai Sea, including those from biomass burning and industrial activities. These findings emphasize the considerable influence of human-induced sources in the Bohai Sea on neighboring urban areas. Furthermore, being a maritime region, natural sources like sea salt and dust from the sea may also exert a discernible impact on the neighboring environment.

The Joint Clean Air Actions and air quality spillovers in China

Facing severe air pollution in its North Plain, the central government of China initiated the Joint Clean Air Action (JCAA) in 2017 to facilitate pollution mitigation efforts across the region. While quite a few studies investigated the effectiveness of this regulation, much less attention is paid to the pollution spillover effects. We empirically examine the effects, and show that 1) air quality in the east of the target cities has been improved due to positive spillover of improved air quality under the JCAA; 2) the beneficiary spillover lasts for two seasons and disappeared in autumn and winter; 3) air quality in the north, south and west directions are almost not changed; 4) wind direction and topography, two determinants of atmospheric transport, have a considerable influence over the spillover effects. Our study provides a fresh perspective to understand the impacts of the JCAA policy and underlines the necessity of taking both pollution and air quality spillover effects into the cost-benefit analysis.Implications: Pollution regulations in one place may increase pollution in other places, as production and emissions are re-allocated under the incentives induced by regional-specific regulations. This phenomenon has long been recognized in the literature as pollution spillover. However, if the relevant production and emissions are not re-allocated, at least not re-allocated in large quantities, local air quality improvement induced by regulations may also benefit the neighboring areas. We call this effect air quality spillover. Both spillover effects should be rigorously evaluated, which is of scientific interest by itself and also contributes to a comprehensive cost-benefit analysis of environmental regulations.

Adverse impacts of Asian dust events on human health and the environment-A probabilistic risk assessment study on particulate matter-bound metals and bacteria in Seoul, South Korea

This study aimed to assess the impact of Asian dust (AD) on the human health and the environment. Particulate matter (PM) and PM-bound trace elements and bacteria were examined to determine the chemical and biological hazards associated with AD days and compared with non-AD days in Seoul. On AD days, the mean PM10 concentration was ∼3.5 times higher than that on non-AD days. Elements generated from the Earth's crust (Al, Fe, and Ca) and anthropogenic sources (Pb, Ni, and Cd) were identified as major contributors to coarse and fine particles, respectively. During AD days, the study area was recognized as "severe" for pollution index and pollution load index levels, and "moderately to heavily polluted" for geoaccumulation index levels. The potential cancer risk (CR) and non-CR were estimated for the dust generated during AD events. On AD days, total CR levels were significant (in 1.08 × 10^-5-2.22 × 10^-5), which were associated with PM-bound As, Cd, and Ni. In addition, inhalation CR was found to be similar to the incremental lifetime CR levels estimated using the human respiratory tract mass deposition model. In a short exposure duration (14 days), high PM and bacterial mass deposition, significant non-CR levels, and a high presence of potential respiratory infection-causing pathogens (Rothia mucilaginosa) were observed during AD days. Significant non-CR levels were observed for bacterial exposure, despite insignificant levels of PM10-bound elements. Therefore, the substantial ecological risk, CR, and non-CR levels for inhalation exposure to PM-bound bacteria, and the presence of potential respiratory pathogens, indicate that AD events pose a significant risk to both human lung health and the environment. This study provides the first comprehensive examination of significant non-CR levels for bacteria and carcinogenicity of PM-bound metals during AD events.

Assessment of air quality in North Korea from satellite observations

North Korea's air quality is poorly understood due to a lack of reliable data. Here, we analyzed urban- to national-scale air quality changes in North Korea using multi-year satellite observations. Pyongyang, Nampo, Pukchang, and Munchon were identified as pollution hotspots. On a national scale, we found that North Korea experienced 6.7, 17.8, and 20.6 times greater amounts of nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and carbon monoxide (CO) per unit primary energy supply (PES) than South Korea from 2005 to 2018. Besides, North Korea had a 24.3 times larger aerosol optical depth (AOD) per PES than South Korea from 2011 to 2018. Severe CO and aerosol pollution is aligned with extensive biofuel combustion. High SO₂ pollution corresponds with the strong coal dependence of the industry. The change rates of the national average columns for NO₂, SO₂, and CO were + 3.6, -4.4, and -0.4 % yr^-1, respectively. The AOD change rate was -4.8 % yr^-1. Overall decreasing trends, except for NO₂, are likely due to a decline in coal-fired PES. Positive NO₂ trends are consistent with increasing industrial activities. Each pollutant showed consistent patterns of linear trends, even after correcting the influence of transboundary pollution. Flue gas control and biofuel consumption reduction seem necessary to improve North Korea's air quality.

Long-Term Trend of the Levels of Ambient Air Pollutants of a Megacity and a Background Area in Korea

It is imperative to understand the changes of the levels of air pollutants in Northeast Asia with respect to the changes of the emissions of air pollutants. In this study, we analyzed long-term trends of both the chemical composition of fine particles and gaseous species in Seoul, a megacity, and Baengnyeong Island, a background area located in the Yellow Sea of Republic of Korea (South Korea) from 2012 to 2019. Long-term changes of the concentrations of air pollutants were analyzed using the Mann–Kendall trend test and Sen’s slope. Since the SO2 emissions in this region have been significantly reduced during last decade, NO3– has become the major species of fine particles instead of SO42–. Seoul and Baengnyeong Island are rich in NH4+ in the atmosphere, and due to the SO2 emission reduction, the balance of ammonia–nitric acid–sulfuric acid has been changed, and the concentration of NO3– has increased. This trend is more obvious in Baengnyeong Island than Seoul due to the lower local emissions in Baengnyeong Island. As a result of this study, it is possible to confirm that concentrations of air pollutants and the majority of aerosols affecting PM2.5 concentrations in Northeast Asia have changed according to the changes in emissions in this region.

Identification of source areas of polycyclic aromatic hydrocarbons in Ulsan, South Korea, using hybrid receptor models and the conditional bivariate probability function

This study identifies the emission source areas for the atmospheric polycyclic aromatic hydrocarbons (PAHs) detected in Ulsan, South Korea. To achieve this, in addition to a conditional bivariate probability function (CBPF), two hybrid receptor models - the three-dimensional potential source contribution function (3D-PSCF) model and the 3D concentration weighted function (3D-CWT) model - were used, both of which adopt trajectory segments within the mixing layer. Notably, the fraction-weighted trajectory (FWT), a combination of PAH gas/particle partitioning with a hybrid receptor model, was introduced for the first time in this study to support the identification of emission source areas using other approaches (i.e., 3D-PSCF, 3D-CWT, and CBPF). Consequently, it was found that gaseous PAHs in Ulsan mostly originated from local emission sources (i.e., transportation and industrial emissions) throughout the year, whereas particulate PAHs were likely to originate from emission sources in China (e.g., Shandong, Hebei, and Liaoning) during spring and winter via long-range transport. However, in summer and fall, the influence of local emissions on particulate PAHs appeared to be stronger. The FWT was able to distinguish between local and distant sources more effectively, especially in summer and fall, i.e., the periods when local sources increased their contribution. This study thus increases the understanding of the long-range transport of PAHs in Northeast Asia, and the novel FWT approach exhibits the potential to be employed in the source area identification of various semi-volatile organic chemicals.

Effect of filter collection efficiency on the clean air delivery rate in an air cleaner

The performance of an air cleaner is evaluated by the clean air delivery rate (CADR), which is defined as the measure of the delivery of contaminant-free air. Herein, we conducted comparative analyses of various particulate air filters with various collection efficiencies. We installed each filter in identical commercial air cleaners to determine the effects of the collection efficiency on the CADR. Three different filters (E11, E12, and H13 classes) were prepared to determine the effects of the filter collection efficiency and pressure drop on the air cleaner performance (ie, the CADR). Based on experimental data, filters E11 and E12 had similar CADRs and flow rates. However, filter H13, which had the highest collection efficiency and the lowest flow rate, had the lowest CADR. This indicates that even if a filter with higher collection efficiency is installed in an air cleaner, the larger pressure drop causes a reduction in the air flow rate. The CADR value is widely distributed for a flow rate range for commercially available models; however, the collection efficiencies for most air cleaners on the market lie in a narrow range. Therefore, the flow rate has the most direct impact on the performance of a commercial air cleaner.

Role of sea fog over the Yellow Sea on air quality with the direct effect of aerosols

In this study, we investigate the impact of sea fog over the Yellow Sea on air quality with the direct effect of aerosols for the entire year of 2016. Using the WRF-CMAQ two-way coupled model, we perform four model simulations with the up-to-date emission inventory over East Asia and dynamic chemical boundary conditions provided by hemispheric model simulations. During the spring of 2016, prevailing westerly winds and anticyclones caused the formation of a temperature inversion over the Yellow Sea, providing favorable conditions for the formation of fog. The inclusion of the direct effect of aerosols enhanced its strength. On foggy days, we find dominant changes of aerosols at an altitude of 150-200 m over the Yellow Sea resulted by the production through aqueous chemistry (~12.36% and ~3.08% increases in sulfate and ammonium) and loss via the wet deposition process (~-2.94% decrease in nitrate); we also find stronger wet deposition of all species occurring in PBL. Stagnant conditions associated with reduced air temperature caused by the direct effect of aerosols enhanced aerosol chemistry, especially in coastal regions, and it exceeded the loss of nitrate. The transport of air pollutants affected by sea fog extended to a much broader region. Our findings show that the Yellow Sea acts as not only a path of long-range transport but also as a sink and source of air pollutants. Further study should investigate changes in the impact of sea fog on air quality in conjunction with changes in the concentrations of aerosols and the climate.

Discrepancy between scientific measurement and public anxiety about particulate matter concentrations

This study presents the characteristics and relevance of air quality in the sensitive public environment by analyzing scientific observations and social data detailing the present status of particulate matter (PM) concentrations alongside the changes in the public perception. By projecting time-series data under the same conditions over long periods of time, the difference between the clarity in the information provided by the media and scientific data was quantified, and the patterns in these fields were identified. We confirmed that the PM mass loads in the atmosphere and column concentrations continue to decrease whereas the number of media articles and internet searches with related key words increased over the same period. It was observed that the number of articles in the media increased by 10.5 times over the same period in which the PM mass in the atmosphere decreased by approximately 2.5%. The correlation analysis between the scientific observation data and social data showed significant correlation for the pairs of PM₁₀ and aerosol optical thickness (AOT), meteorological visibility and relative humidity, and media publications with the number of internet portal searches. These results indicate that individual interest and anxiety about the air quality increased quantitatively as a result of these issues being mentioned in new media sources. These results demonstrate the reasons why atmospheric scientists should provide more information about current air quality to the public and exert their professionality in scientific and public discourse.

Role of emissions and meteorology in the recent PM2.5 changes in China and South Korea from 2015 to 2018

In this study, we examined the change rates of PM_2.5 concentrations, aerosol optical depth (AOD), and the concentrations of PM_2.5 precursors, such as SO₂ and NO₂, in China and South Korea using surface and satellite observations from 2015 to 2018. To quantify the impacts of the emissions and meteorology on the concentration changes, we performed a series of air quality simulations with year-specific meteorology and a fixed anthropogenic emissions inventory. The surface PM_2.5 observations in China and South Korea decreased at rates of 9.1 and 4.3%/yr during the study period, respectively. The AODs from Moderate Resolution Imaging Spectroradiometer (MODIS) and Geostationary Ocean Color Imager (GOCI) also decreased faster over China than the AODs over South Korea. For the PM_2.5 decrease in China, the emission impact was more significant (73%) than the meteorology impact (27%). On the contrary, in South Korea, the emissions and meteorology impacts on PM_2.5 reductions were similar (51% vs 49%). The SO₂ concentration over China in 2018 significantly reduced to approximately half of the level in 2015. In turn, the sulfate concentration in Baengnyeong (BN), located in a downwind pathway from China to South Korea, decreased at a rate of 0.79%/month. However, the nitrate concentration in BN showed an increasing trend due to the non-linear chemical reactions among sulfate-nitrate-ammonium. The increased nitrate compensated for the reduced PM_2.5 concentration from the sulfate decrease at BN. Additionally, the number of high (>50 μg/m³) PM_2.5 concentration days continuously decreased in China, but the number in South Korea increased. It is noted that emission reductions in an upwind area do not guarantee corresponding air quality improvement in the downwind area when complex secondary aerosol formation processes, as well as spatiotemporal changes in meteorology, are involved in the transboundary transport of air pollutants.

Light absorption enhancement of particulate matters and their source apportionment over the Asian continental outflow site and South Yellow Sea

Light absorption enhancement of black carbon due to the aerosol mixing states is an important parameterization for climate modeling, while emission source contributions to the enhancement factor are unclear. An intensive campaign was conducted simultaneously at a China coastal site (Qingdao city) and maritime sites (South Yellow Sea, SYS) in August and Nov to Dec 2018. The absorption enhancement (E_MAC) of the black carbon was calculated using a two-step solvent dissolution protocol and found 1.96 ± 0.68, 1.64 ± 0.38, and 2.40 ± 0.76 for Qingdao summer (QS), Qingdao autumn (QA), and SYS, respectively. Positive matrix factorization (PMF) model identified six sources of PM_2.5 and E_MAC, which were secondary aerosol (with contribution 27.9% and 29.2%), coal combustion (24.9% and 20.2%), industrial emissions (15.2% and 25.4%), sea salt (6.9% and 9.6%), vehicle emissions (12.1% and 10.9%), and soil dust (13.0% and 4.7%), respectively. These sources increased the absorption of black carbon by a factor of 1.25 ± 0.11 (secondary aerosol), 1.21 ± 0.20 (industrial emissions), 1.17 ± 0.08 (coal combustion), 1.09 ± 0.07 (vehicle emissions), 1.08 ± 0.17 (sea salt), and 1.04 ± 0.10 (soil dust). Based on the correlation between PM and E_MAC source contributions, we estimated that secondary aerosols, industrial emissions, and coal combustion contributed to 74.8% of absorption enhancement at a regional scale in China. The source apportionment for E_MAC offers a new diagnosis for each source regarding aerosol forcing simulation which inputs from the individual emission sector.

Assessment of long-range transboundary aerosols in Seoul, South Korea from Geostationary Ocean Color Imager (GOCI) and ground-based observations

To better understand air quality issues in South Korea, it is essential to identify the main contributors of air pollution and to quantify the effects of transboundary transport. In this study, geostationary satellite measurements were used to assess the effects of aerosol transport on air quality in South Korea. This study proposes a method to define the long-range transport (LRT) of aerosols into the Korean Peninsula using remote sensing obervations and back-trajectories and estimates the LRT effects on air quality in Seoul using in-situ particulate matter (PM) measurements. Aerosol optical depths (AODs) are obtained from the Geostationary Ocean Color Imager (GOCI), and the back-trajectories are from the National Ocean and Atmospheric Administration (NOAA) HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. For LRT events, satellite observations showed high AOD plumes over the Yellow Sea, a pathway between Eastern China and South Korea, and the movements of aerosol plumes transported to South Korea were also detected. PM_2.5 concentrations, PM₁₀ concentrations, and AOD during LRT increased by 52%, 49%, and 81%, respectively, relative to their average values for 2015-2018. To quantitatively characterize the LRT of aerosols, the effects of LRT on PM_2.5 concentrations were estimated for each PM concentration category. The contribution of LRT to PM_2.5 concentrations was estimated to be 33% during 2015-2018. When high concentrations of PM_2.5 were observed in Seoul, they were likely to be associated with LRT events.

Direct and cross impacts of upwind emission control on downwind PM2.5 under various NH3 conditions in Northeast Asia

Emissions reductions in upwind areas can influence the PM_2.5 concentrations in downwind areas via long-range transport. However, few studies have assessed the impact of upwind PM_2.5 precursor controls on changes in downwind PM_2.5 concentrations. In this study, we analyzed the overall impact of PM_2.5 precursor emission controls in upwind areas on PM_2.5 in downwind areas with two types of impacts: "direct impact" and "cross impact." The former refers to PM_2.5 changes in downwind areas due to the transported PM_2.5 itself, whereas the latter represents PM_2.5 changes due to reactions between the transported gaseous precursors and intermediates (i.e., HNO₃) originating from upwind areas and locally emitted precursors (i.e. NH₃) in the downwind areas. As a case study, we performed air quality modeling for Northeast Asia for January 15-17, 2016 by setting China and South Korea as the upwind and downwind areas, respectively. To account for potential spatiotemporal variations in NH₃ emissions in downwind areas, we considered two NH₃ conditions. When NOx emissions in China were reduced by 35%, in downwind areas the PM_2.5 concentrations decreased by 2.2 μg/m³ under NH₃-rich conditions, while PM_2.5 concentrations increased by 2.3 μg/m³ under NH₃-poor conditions. The direct impact increased by 4.0 μg/m³ in both cases due to upwind NO_x disbenefit effects. However, the cross impacts led to a PM_2.5 decrease of 6.2 μg/m³ under NH₃-rich conditions versus a PM_2.5 increase of 1.7 μg/m³ under NH₃-poor conditions. We noted that PM_2.5 concentrations in the downwind areas may not improve unless a cross impact outweighs a direct impact. This may be one of the reasons why South Korea PM_2.5 concentrations have not declined despite efforts by China to reduce their PM_2.5 precursor emissions.

The implication of the air quality pattern in South Korea after the COVID-19 outbreak

By using multiple satellite measurements, the changes of the aerosol optical depth (AOD) and nitrogen dioxide (NO₂) over South Korea were investigated from January to March 2020 to evaluate the COVID-19 effect on the regional air quality. The NO₂ decrease in South Korea was found but not significant, which indicates the effects of spontaneous social distancing under the maintenance of ordinary life. The AODs in 2020 were normally high in January, but they became lower starting from February. Since the atmosphere over Eastern Asia was unusually stagnant in January and February 2020, the AOD decrease in February 2020 clearly reveals the positive effect of the COVID-19. Considering the insignificant NO₂ decrease in South Korea and the relatively long lifetime of aerosols, the AOD decrease in South Korea may be more attributed to the improvement of the air quality in neighboring countries. In March, regional atmosphere became well mixed and ventilated over South Korea, contributing to large enhancement of air quality. While the social activity was reduced after the COVID-19 outbreak, the regional meteorology should be also examined significantly to avoid the biased evaluation of the social impact on the change of the regional air quality.

Correcting model biases of CO in East Asia: impact on oxidant distributions during KORUS-AQ

Global coupled chemistry-climate models underestimate carbon monoxide (CO) in the Northern Hemisphere, exhibiting a pervasive negative bias against measurements peaking in late winter and early spring. While this bias has been commonly attributed to underestimation of direct anthropogenic and biomass burning emissions, chemical production and loss via OH reaction from emissions of anthropogenic and biogenic volatile organic compounds (VOCs) play an important role. Here we investigate the reasons for this underestimation using aircraft measurements taken in May and June 2016 from the Korea-United States Air Quality (KORUS-AQ) experiment in South Korea and the Air Chemistry Research in Asia (ARIAs) in the North China Plain (NCP). For reference, multispectral CO retrievals (V8J) from the Measurements of Pollution in the Troposphere (MOPITT) are jointly assimilated with meteorological observations using an ensemble adjustment Kalman filter (EAKF) within the global Community Atmosphere Model with Chemistry (CAM-Chem) and the Data Assimilation Research Testbed (DART). With regard to KORUS-AQ data, CO is underestimated by 42% in the control run and by 12% with the MOPITT assimilation run. The inversion suggests an underestimation of anthropogenic CO sources in many regions, by up to 80% for northern China, with large increments over the Liaoning Province and the North China Plain (NCP). Yet, an often-overlooked aspect of these inversions is that correcting the underestimation in anthropogenic CO emissions also improves the comparison with observational O₃ datasets and observationally constrained box model simulations of OH and HO₂. Running a CAM-Chem simulation with the updated emissions of anthropogenic CO reduces the bias by 29% for CO, 18% for ozone, 11% for HO₂, and 27% for OH. Longer-lived anthropogenic VOCs whose model errors are correlated with CO are also improved, while short-lived VOCs, including formaldehyde, are difficult to constrain solely by assimilating satellite retrievals of CO. During an anticyclonic episode, better simulation of O₃, with an average underestimation of 5.5 ppbv, and a reduction in the bias of surface formaldehyde and oxygenated VOCs can be achieved by separately increasing by a factor of 2 the modeled biogenic emissions for the plant functional types found in Korea. Results also suggest that controlling VOC and CO emissions, in addition to widespread NO _x controls, can improve ozone pollution over East Asia.

Impact of the COVID-19 Outbreak on Air Quality in Korea

The COVID-19 pandemic has led countries to take action, which has included practicing social distancing or lockdown. Many cities are experiencing air quality improvements due to human activity restrictions. The purpose of this study was to compare the air quality between 2020 and the previous three years, focusing on the two cities (Seoul and Daegu) where coronavirus is spreading the fastest in Korea. Significant decreases in PM2.5, PM10, CO, and NO2 were observed in both cities. In particular, compared to the same period of 2017-2019, in March 2020, PM2.5 showed remarkable reductions of 36% and 30% in Seoul and Daegu, respectively. The effects of social distancing have maximized improvements in air quality due to reduced transboundary pollutants. The PM2.5/PM10 ratio was significantly reduced after social distancing, indicating that the contribution of traffic-related PM2.5 declined. Air quality improved overall from January to July, and the most noticeable drop in the air quality index (AQI) was observed in April. These findings indicate that relatively weak social distancing measures compared to a COVID-19 lockdown can help reduce air pollutant levels. At the same time, however, changes in air quality in the neighboring countries caused by COVID-19 control action are affecting Korea.

Spatial variability of sedimentary carbon in South Yellow Sea, China: impact of anthropogenic emission and long-range transportation

During the last few decades, sedimentary carbons gain great concerns of research interest among the scientific committee worldwide due to their adverse impact on aquatic chemistry, ecology, and hence human health along with global climate change. In the present study, we investigated the spatial distribution of mass concentration of sedimentary carbon (viz. black carbon: BC, and its components, char and soot) along with their burial fluxes in the surface sediments of the South Yellow Sea (SYS). The concentration of sedimentary carbon is measured by using an emerging method of thermal/optical reflectance. The observed BC concentration is found in the range of 0.02-1.02 mg g^-1 with a mean value of 0.49 ± 0.26 mg g^-1. The mean burial fluxes of BC, char, and soot also have a similar spatial variation to their concentration with the mean value along with relative standard deviation (in bracket) 22.43 ± 12.49 (~ 56%), 5.90 ± 3.99 (~ 68%), and 16.53 ± 10.67 (65%), respectively. Relatively lower value of char/soot ratio, i.e., 0.48 ± 0.22, indicates the dominance of soot in surface sediments that could be mainly derived from the fossil fuel combustion which is further confirmed from emission inventory data suggesting maximum contribution, i.e., ~ 66-80%, of the total BC emission emitted from residential and industrial emission sources. The back trajectories analysis revealed a significant impact of long-range transportation on BC concentration in the surface sediments of SYS. Further study of BC concentrations in sea sediments and their interaction with other organic/inorganic compounds in continental shelves is highly needed for a better understanding of the global carbon cycle.