Abstract
In this study, the chemical components of aerosols observed at ground level and in upper layers during the Korea–United States Air Quality (KORUS-AQ) campaign were analyzed in two representative metropolitan areas of Korea: the Seoul metropolitan area (SMA) and the Busan-containing southeastern metropolitan area (BMA). First, we characterized emissions using the Clean Air Policy Support System (CAPSS) emission statistics, and compared them with both ground- and aircraft-based measurements obtained during the KORUS-AQ campaign. The emission statistics showed that the SMA had higher NOx levels, whereas BMA had significantly higher SO2 levels. Ground-level observations averaged for the summer season also showed SMA–nitrate and BMA–sulfate relationships, reflecting the CAPSS emission characteristics of both areas. However, organic carbon (OC) was higher in BMA than SMA by a factor of 1.7, despite comparable volatile organic compound (VOC) emissions in the two areas. DC-8 aircraft-based measurements showed that, in most cases, nitrogen-rich localities were found in the SMA, reflecting the emission characteristics of precursors in the two sampling areas, whereas sulfur-rich localities in the BMA were not apparent from either ground-based or aircraft observations. KORUS-AQ measurements were classified according to two synoptic conditions, stagnant (STG) and long-range transport (LRT), and the nitrate-to-sulfate (N/S) ratio in both ground and upper layers was higher in the SMA for both cases. Meanwhile, organic aerosols reflected local emissions characteristics in only the STG case, indicating that this stagnant synoptic condition reflect local aerosol characteristics. The LRT case showed elevated peaks of all species at altitudes of 1.0–3.5 km, indicating the importance of LRT processes for predicting and diagnosing aerosol vertical distributions over Northeast Asia. Other chemical characteristics of aerosols in the two metropolitan areas were also compared.
Highlights
Particulate matter less than 2.5 μm in size (PM2.5 ) in the atmosphere is directly emitted as a pollutant through processes such as fossil fuel combustion in factories and automobiles, and is generated secondarily through atmospheric chemical reactions from gas-phase precursors
The present study explores the DC-8 aircraft measurements of PM2.5 chemical components obtained during the KORUS-AQ campaign over the Busan-containing southeastern metropolitan area (BMA), and assesses the vertical structures through comparisons with those in the Seoul metropolitan area (SMA)
We explored the emissions characteristics in two areas, SMA and BMA, through the assessment of the annual total nitrogen oxides (NOx), SOx, and volatile organic compound (VOC) emissions according to Clean Air Policy Support System (CAPSS)
Summary
Particulate matter less than 2.5 μm in size (PM2.5 ) in the atmosphere is directly emitted as a pollutant through processes such as fossil fuel combustion in factories and automobiles, and is generated secondarily through atmospheric chemical reactions from gas-phase precursors. During the KORUS-AQ campaign, both in situ surface measurements and aircraft observations of the upper layers were collected concerning air pollutants, including secondarily generated aerosols, VOCs, ozone, and cloud condensation nuclei (CCN), and some impact analysis studies were conducted in the main metropolitan area [11,12,13,14,15]. In the absence of other observations, the DC-8 aircraft measurements obtained during the KORUS-AQ campaign allow for the analysis of vertical PM2.5 structures from disaggregated chemical components using both ground measurements and aircraft observations (measurements of upper layers) Such paired aerosol measurements, coupling and integrating data from the surface (or lower atmosphere) to the upper layer, can be used to determine source distributions such as industrial complexes, port facilities, and thermal power plants, as well as external PM2.5 inflow routes in the real atmosphere, which are essential for understanding aerosol features from a source and receptor perspective. Atmosphere 2021, 12, 1451 ments were taken in SMA and BMA, and compared in terms of the distributions of mass and chemical components, as well as associations with local circulation patterns
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