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According to the 2017 National Air Pollutant Emissions Inventory (NEI), air pollutant emissions in the Republic of Korea comprised 817,420 metric tons (hereafter tons) of CO, 1,189,800 tons of NOx, 315,530 tons of SOx, 592,582 tons of TSP, 218,476 tons of PM10, 91,731 tons of PM2.5, 15,555 tons of black carbon (BC), 1,047,585 tons of VOCs, and 308,298 tons of NH3. Emissions of the 13 first-level emission source categories, which constitute the NEI, were estimated and, based on their characteristics, the emission source categories were grouped into five sectors (energy, industry, road, non-road, and everyday activities and others). In addition, the contributions of primary PM2.5 and its four precursors (NOx, SOx, VOCs, and NH3) to the 2017 NEI were assessed in this study. The emission contributions of NOx to the NEI were 36.5% for the road sector, which was the highest of those of all the air pollutants for this sector; NOx emissions for this sector were 4.2% lower than those in the previous year. The emission contributions of SOx and PM2.5 to the NEI were higher than those of the other air pollutants for the industry sector; SOx and PM2.5 emissions for this sector decreased by 9.8% and 19.7%, respectively, compared with those in the previous year. The emission contributions of VOCs and NH3 to the NEI were 65.3% and 83.9% for the everyday activities and others sector, respectively, higher than those of the other air pollutants for this sector; VOCs and NH3 emissions for this sector increased by 0.8% and 2.9%, respectively, compared with those in the previous year. A three-dimensional (3D) chemical transport modeling system was used to validate the emission estimates. These data suggest that simulated SOx emissions were overestimated in areas with dense large-scale industrial complexes, such as Jeollanam-do, Gyeongsangbuk- do, and Ulsan, and that simulated NOx emissions were overestimated in Seoul, Incheon, and Jeollanam-do.

The nation-wide PM2 5 concentration from December 2019 to March 2020 (2019 Winter) in South Korea was observed as low as 24 mu g/m(3), showing the lowest seasonal mean PM2 5 concentrations for the last five years Consequently, the PM2 5 concentration during the Seasonal Management has dropped by 26% and 23% compared to those for the same months in 2018 (2018 Winter), and the previous three years (2016 similar to 2018), respectively In this study, the observations and air quality simulations with a set of fixed anthropogenic emissions were incorporated to quantitatively separate the meteorology and emission influences on the PM2 5 change in South Korea during the 2019 Winter The results show that meteorology and emission-driven influence has decreased the national mean PM2 5 concentrations during the 2019 Winter by 9% and 18%, respectively when compared to the 2018 Winter On the other hand, the same comparison to PM2 5 concentrations for the previous three years explained approximately 2% increase and 24% drop with meteorology and emission-driven influence, respectively Monthly mean PM2 5 changes have varied for each month and exhibited the largest drop in February 2020 by 24% when compared to February 2019 (a 27% drop from the previous 3-year mean for the month) It may reflect the abrupt PM2 5-related emission reductions in Northeast Asia after the COVID-19 pandemic Air quality simulations with perturbed emissions presented that an increase of South Korean domestic impact and a decrease of foreign emission impact between the 2018 and 2019 Winters It represents that South Korean domestic efforts to reduce PM2 5 concentrations become more efficient under the meteorology condition during the 2019 Winter

The atmospheric mineral aerosol reaction (AMAR) model, which was developed to simulate dust-driven heterogeneous chemistry of SO2 and NOx, was combined with the comprehensive air quality model with...

The Korea-United States Air Quality (KORUS-AQ) field study was conducted during May–June 2016 to understand the factors controlling air quality in South Korea. Extensive aircraft and ground network observations from the campaign offer an opportunity to address issues in current air quality models and reduce model-observation disagreements. This study examines these issues using model evaluation against the KORUS-AQ observations and intercomparisons between models. Six regional and two global chemistry transport models using identical anthropogenic emissions participated in the model intercomparison study and were used to conduct air quality simulations focusing on ozone (O3), aerosols, and their precursors for the campaign. Using the KORUSv5 emissions inventory, which has been updated from KORUSv1, the models successfully reproduced observed nitrogen oxides (NOx) and volatile organic compounds mixing ratios in surface air, especially in the Seoul Metropolitan Area, but showed systematic low biases for carbon monoxide (CO), implying possible missing CO sources in the inventory in East Asia. Although the DC-8 aircraft-observed O3 precursor mixing ratios were well captured by the models, simulated O3 levels were lower than the observations in the free troposphere in part due to too low stratospheric O3 influxes, especially in regional models. During the campaign, the synoptic meteorology played an important role in determining the observed variability of PM2.5 (PM diameter ≤ 2.5 μm) concentrations in South Korea. The models successfully simulated the observed PM2.5 variability with significant inorganic sulfate-nitrate-ammonium aerosols contribution, but failed to reproduce that of organic aerosols, causing a large inter-model variability. From the model evaluation, we find that an ensemble of model results, incorporating individual models with differing strengths and weaknesses, performs better than most individual models at representing observed atmospheric compositions for the campaign. Ongoing model development and evaluation, in close collaboration with emissions inventory development, are needed to improve air quality forecasting.

Sixty days after the lockdown of Hubei province, where the coronavirus was first reported, China's true recovery from the pandemic remained an outstanding question. This study investigates how human activity changed during this period using observations of surface pollutants. By combining surface data with a three-dimensional chemistry model, the impacts of meteorological variations and variations in yearly emissions control are minimized, demonstrating how pollutant levels over China changed before and after the Lunar New Year from 2017 to 2020. The results show that the reduction in NO2 concentrations, an indicator of emissions in the transportation sector, was clearly deeper and longer in 2020 than in normal years, and started to recover after February 15. By contrast, PM2.5 emissions had not yet recovered by the end of March, showing a reduction around 30 % compared with normal years. SO2 emissions had not affected significantly by the pandemic. Additional model study using a top-down emissions adjustment still confirms a reduction around 25 % in unknown surface PM2.5 emissions over the same period, even after realistically updating SO2 and NOx emissions. This evidence suggests that different economic sectors in China may be recovering at different rates, with the fastest recovery in transportation and a slower recovery likely in agriculture. The apparent difference between the recovery timelines of NO2 and PM2.5 implies that monitoring a single pollutant alone (e.g. NOx emissions) is insufficient to draw conclusions on the overall recovery of the Chinese economy.

Nitrogen oxide (NOx) emissions from the South Korean cement industry are investigated with remote-sensing measurements, surface observations, and in situ aircraft measurements. In the Yeongwol, Danyang, and Jecheon regions of central South Korea, six closely located cement factories produce 31 million tons of cement annually. Their impact on the regional environment has been a public-policy issue, but their pollutants have not been continuously monitored nor have emissions inventories been fully verified. Using a newly developed downscaling technique, remote-sensing analyses show that Ozone Monitoring Instrument (OMI) NO2 column densities over the cement kilns have more than twice the modeled concentrations, indicating that the kilns are one of the most dominant NOx emission point sources in South Korea. Observed NOx emissions are stronger in the spring, suggesting that these sources play an important role in the formation of surface ozone and secondary particulate matter. These emissions also slightly increased in recent years, even while most major South Korean cities posted a declining trend in NOx emissions. Photochemical models (during May to July 2015) demonstrate that emissions from the South Korean cement industry have significant environmental impacts, both on surface ozone (up to approximately 4 ppb) and PM2.5 (up to approximately 2 &micro, g/m3).

The impact of regional emissions (e.g., domestic and international) on surface particulate matter (PM) concentrations in the Seoul metropolitan area (SMA), South Korea, and its sensitivities to meteorology and emissions inventories are quantitatively estimated for 2014 using regional air quality modeling systems. Located on the downwind side of strong sources of anthropogenic emissions, South Korea bears the full impact of the regional transport of pollutants and their precursors. However, the impact of foreign emissions sources has not yet been fully documented. We utilized two regional air quality simulation systems: (1) a Weather Research and Forecasting and Community Multi-Scale Air Quality (CMAQ) system and (2) a United Kingdom Met Office Unified Model and CMAQ system. The following combinations of emissions inventories are used: the Intercontinental Chemical Transport Experiment-Phase B, the Inter-comparison Study for Asia 2010, and the National Institute of Environment Research Clean Air Policy Support System. Partial contributions of domestic and foreign emissions are estimated using a brute force approach, adjusting South Korean emissions to 50 %. Results show that foreign emissions contributed ∼ 60 % of SMA surface PM concentration in 2014. Estimated contributions display clear seasonal variation, with foreign emissions having a higher impact during the cold season (fall to spring), reaching ∼ 70 % in March, and making lower contributions in the summer, ∼ 45 % in September. We also found that simulated surface PM concentration is sensitive to meteorology, but estimated contributions are mostly consistent. Regional contributions are also found to be sensitive to the choice of emissions inventories.

This article presents the results of a detailed source apportionment study of the high particulate matter (PM) event in the Seoul Metropolitan Area (SMA), South Korea, during late February 2014. Using the Comprehensive Air Quality Model with Extensions with its Particulate Source Apportionment Technology (CAMx-PSAT), we defined 10 source regions, including five in China, for spatially and chemically resolved analyses. During the event, the spatially averaged PM10 concentration at all PM10 monitors in the SMA was 129 μg/m3, while the PM10 and PM2.5 concentrations at the BulGwang Supersite were 143 μg/m3 and 123 μg/m3, respectively. CAMx-PSAT showed reasonably good PM model performance in both China and the SMA. For February 23–27, CAMx-PSAT estimated that Chinese contributions to the SMA PM10 and PM2.5 were 84.3 μg/m3 and 80.0 μg/m3, respectively, or 64% and 70% of the respective totals, while South Korea's respective domestic contributions were 36.5 μg/m3 and 23.3 μg/m3. We observed that the spatiotemporal pattern of PM constituent concentrations and contributions did not necessarily follow that of total PM10 and PM2.5 concentrations. For example, Beijing-Tianjin-Hebei produced high nitrate concentrations, but the two most-contributing regions to PM in the SMA were the Near Beijing area and South Korea. In addition, we noticed that the relative contributions from each region changed over time. We found that most ammonium mass that neutralized Chinese sulfate mass in the SMA came from South Korean sources, indicating that secondary inorganic aerosol in the SMA, especially ammonium sulfates, during this event resulted from different major precursors originating from different regions.

Both surface and satellite observations have shown a decrease in NO

Seventeen years (2001–2017) of surface observations and spatial synoptic classification (SSC) data are used to analyze the characteristics of surface ozone concentration according to synoptic weather patterns. While weather conditions are known to play an important role in regional air quality, the extent to which synoptic weather patterns affect the production of high ground-level ozone concentrations has not yet been fully quantified. Using thermal characteristics and geographic origins, the SSC method classifies air masses into six types: dry polar (DP), dry moderate (DM), dry tropical (DT), moist polar (MP), moist moderate (MM), and moist tropical (MT). We link daily maximum 8-h ozone concentrations (MDA8 O3) from 306 monitoring sites to the closest SSC classifications at 17 airport sites and then analyze their association. We find that DM, DT, and MT are commonly associated with high ozone, whereas DT produces ozone with the greatest efficiency, especially high levels of concentration. This finding implies a potentially strong connection between surface ozone and climate change because the occurrence of DT weather has increased by more than three times over the past 50 years in South Korea. Sensitivity tests reveal that mean MDA8 ozone may increase by 3.5% (7.5%) as the DT frequency increases by 200% (300%). The impacts are larger for higher levels of concentration, with 31.7% (63.3%) or more prevalence of the >80 ppb range with the same increased DT frequency. We conclude that synoptic weather and its long-term trends play important roles in the increased surface ozone recently seen in South Korea.

Anthropogenic emissions in East Asia have changed dramatically in recent years. To measure these changing emissions in support of air-quality modeling, we developed a top-down emission update system using surface observations and a geographical information system spatial-allocation technique. We deploy a data-processing system to construct adjustment factors to prefecture-level SO2 emissions by comparing surface and modeled observations. A case study is conducted over East Asia for 2016 in which we update Chinese SO2 emissions using measurements from around 1500 surface monitoring sites. Model simulations using updated SO2 emissions are improved relative to the existing simulation system (e.g., R = 0.23 to R = 0.8), suggesting that the newly designed system provides an efficient, practical forecast solution. Finally, estimated SO2 emissions are compared with existing emission inventories, agreeing well with recent reports of reduced SO2 emissions from Chinese anthropogenic sources.

Both surface and satellite observations have shown a decrease in NOx emissions in East Asian countries in recent years. In order to reflect the recent NOx emission reduction and to investigate its impact on surface O3 concentrations in Asian megacities, we adjusted two bottom-up regional emission inventories of which base years are 2006 (E2006) and 2010 (E2010), respectively. We applied direct and relative emission adjustments to both E2006 and E2010 to constrain NOx emissions using OMI NO2 vertical column densities. Except for the relative emission adjustment with E2006, modeling results with adjusted emissions exhibit that NOx emissions over East Asian megacities (Beijing, Shanghai, Seoul, and Tokyo) in the bottom-up inventories are generally overestimated. When the direct emission adjustment is applied to E2006, model biases in the Seoul Metropolitan Area (SMA), South Korea are reduced from 24 ppb to 2 ppb for NOx (=NO+NO2) and from −9 ppb to 0 ppb for O3. In addition, NO2 model biases in Beijing and Shanghai in China are reduced from 8 ppb to 18 ppb–0 ppb and 1 ppb, respectively. Daily maximum 8-h average O3 model biases over the same places are decreased by 8 ppb and 14 ppb. Further analyses suggest that the reduction in domestic South Korean NOx emissions plays a significant role in increasing O3 concentrations in SMA. We conclude that the current strong drive to reduce NOx emissions as part of the strategy to lower particulate matter concentrations in South Korea can account for increased O3 concentrations in recent years and suggest that more aggressive NOx emissions will be necessary soon.

This study identified the key chemical components based on an analysis of the seasonal variations of ground level PM2.5 concentrations and its major chemical constituents (sulfate, nitrate, ammonium, organic carbon, and elemental carbon) in the Seoul Metropolitan Area (SMA), over a period of five years, ranging from 2012 to 2016. It was found that the mean PM2.5 concentration in the SMA was 33.7 &mu, g/m3, while inorganic ions accounted for 53% of the total mass concentration. The component ratio of inorganic ions increased by up to 61%&ndash, 63% as the daily mean PM2.5 concentration increased. In spring, nitrate was the dominant component of PM2.5, accounting for 17%&ndash, 32% of the monthly mean PM2.5 concentrations. In order to quantify the impact of long-range transport on the SMA PM2.5, a set of sensitivity simulations with the community multiscale air-quality model was performed. Results show that the annual averaged impact of Chinese emissions on SMA PM2.5 concentrations ranged from 41% to 44% during the five years. Chinese emissions&rsquo, impact on SMA nitrate ranged from 50% (winter) to 67% (spring). This result exhibits that reductions in SO2 and NOX emissions are crucial to alleviate the PM2.5 concentration. It is expected that NOX emission reduction efforts in China will help decrease PM2.5 concentrations in the SMA.

The impact of regional emissions (e.g., domestic and international) on surface particulate matter (PM) concentrations in the Seoul Metropolitan Area (SMA), South Korea and its sensitivities to meteorology and emissions inventories are quantitatively estimated for 2014 using regional air quality modeling systems. Located on the downwind side of strong sources of anthropogenic emissions, South Korea bears the full impact of the regional transport of pollutants and their precursors. However, the impact of foreign emission sources have not yet been fully documented. We utilized two regional air quality simulation systems: (1) a Weather Research and Forecasting and Community Multi-Scale Air Quality (CMAQ) system; and (2) a United Kingdom Met Office Unified Model and CMAQ system. The following combinations of emission inventories are used: the Intercontinental Chemical Transport Experiment-Phase B, Inter-comparison Study for Asia 2010, and the National Institute of Environment Research Clean Air Policy Support System. Partial contributions of domestic and foreign emissions are estimated using a brute force approach, adjusting South Korean emissions to 50 %. Results show that foreign emissions contributed ~ 65 % of SMA surface PM concentration in 2014. Estimated contributions display clear seasonal variation, with foreign emissions having a higher impact during the cold season (Fall to Spring), reaching ~ 80 % in March, and making lower contributions in the summer, ~ 40 % in July. We also found that simulated surface PM concentration is sensitive to meteorology, but estimated contributions are mostly robust. Regional contributions are also found to be sensitive to the choice of emissions inventories.

Recent changes of surface particulate matter (PM) concentration in the Seoul Metropolitan Area (SMA), South Korea, are puzzling. The long-term trend of surface PM concentration in the SMA declined in the 2000s, but since 2012 its concentrations have tended to incline, which is coincident with frequent severe hazes in South Korea. This increase puts the Korean government’s emission reduction efforts in jeopardy. This study reports that interannual variation of surface PM concentration in South Korea is closely linked with the interannual variations of wind speed. A 12-year (2004–2015) regional air quality simulation was conducted over East Asia (27-km) and over South Korea (9-km) to assess the impact of meteorology under constant anthropogenic emissions. Simulated PM concentrations show a strong negative correlation (i.e. R = −0.86) with regional wind speed, implying that reduced regional ventilation is likely associated with more stagnant conditions that cause severe pollutant episodes in South Korea. We conclude that the current PM concentration trend in South Korea is a combination of long-term decline by emission control efforts and short-term fluctuation of regional wind speed interannual variability. When the meteorology-driven variations are removed, PM concentrations in South Korea have declined continuously even after 2012.

We demonstrate that daily pollutant transport patterns in East Asia are visible from satellite images when inspected with corresponding synoptic weather analyses. Transport pathways of air pollutants in East Asia are investigated using satellite observations, surface weather charts, and chemical-transport model simulations. It is found that during cool season (fall to spring), pollutant transports in East Asia are largely determined by synoptic weather patterns associated with high pressure system over southern China, which is extended from the Siberia High, and low pressure system over Manchuria, which is initiated by Altai-Sayan cyclogenesis. Based on the relative location and strength of these weather systems, three types of synoptic weather patterns that may contribute to pollutants transport in East Asia, especially in China and Korea, are identified: i.e., (1) a strengthening of the Siberian High and its southeastward propagation; (2) a high-pressure system over southern China followed by a frontal passage associated with a northern low-pressure system; and (3) a stagnant high-pressure system over southern China. For all three patterns, the high-pressure system in southern China is essential for the development of regional air pollution, while frontal activities associated with low-pressure system provide a forcing mechanism to transport those pollutants eastward or southeastward. Observed and simulated surface PM distributions show good agreement in both aerosol optical depth and NO2 column density further implying that anthropogenic emissions also contribute to regional events of high surface PM concentrations. It is argued that the quasi-periodic migration of synoptic weather systems in East Asia works as an efficient pump of pollutants; i.e., regional air pollutions developed under high-pressure systems are transported downstream by low-pressure systems.