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, which occurred on 9 June 2016, reveals that
increased levels of biogenic emissions, in combination with amplified urban
emissions, were associated with severe levels of pollution and a regulatory
exceedance at TRF. In summary, domestic emissions may be causing more
pollution than by transboundary 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.
Observations of massive air-pollution transport and associated air quality in the Yellow Sea region
