Abstract
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 of ozone 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 Yellow 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. In summary, domestic emissions may be causing more pollution than by trans-boundary pathways, which have been historically believed to be the major source of air pollution in South Korea. 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.
Highlights
The spatiotemporal characteristics of ozone (O3), nitrogen dioxide (NO2) and other urban pollutants have been monitored at the ground level within the Seoul Metropolitan Area (SMA) and throughout the Republic of Korea for several decades (Seo et al, 2014)
As part of the KORUS-AQ study, nearly continuous chemical measurements at the surface and within the first 3 km a.s.l. have quantified several of the key pollution features responsible for O3 exceedances observed at a rural site downwind of Seoul
The combination of aircraft (NASA DC-8, Hanseo University King Air, and National Aeronautics and Space Administration (NASA) B-200), in situ and remotely sensed (O3 lidar, ceilometer) measurements, in conjunction with photochemical model simulations, have produced significant findings about the origins of pollution reaching Taehwa Research Forest (TRF) that appear to be representative of other rural sites in South Korea
Summary
The spatiotemporal characteristics of ozone (O3), nitrogen dioxide (NO2) and other urban pollutants have been monitored at the ground level within the Seoul Metropolitan Area (SMA) and throughout the Republic of Korea (commonly referred to as South Korea) for several decades (Seo et al, 2014). More recent findings describe the highest O3 events occurring at rural sites 30 km (Taehwa Forest: TRF, 37.3123◦ N, 127.3106◦ E, 160 m a.s.l.; Kim et al, 2013) and 100 km (Chuncheon, 37.881◦ N, 127.676◦ E; Jeon et al, 2014) from the SMA Both of those studies linked the high-pollution events to mobile (vehicular) source emissions in the presence of natural biogenic emissions (i.e., advection of SMA emissions away from their origins and into a highBVOC environment of increased O3 production efficiency). 3.3) of the 11 TRF 1 h exceedances are examined with aircraft and ground-based measurements including O3 lidar and ceilometer backscatter profiles These are complemented by a photochemical box model used to calculate net O3 production and are used distinguish urban and industrial emissions from one of mixed urban and biogenic origins These are complemented by a photochemical box model used to calculate net O3 production and are used distinguish urban and industrial emissions from one of mixed urban and biogenic origins (Sect. 4)
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