5B: Results from KORUS-AQ to guide air quality improvement in Korea

ACOM scientists participated in, and continue to analyze results from, the KORUS-AQ field campaign, jointly led by NASA and Korean agencies and universities in May-June 2016 in South Korea.  One area of analysis is using the WRF Tracer forecast (provided to support flight planning during the campaign) to explore the role of transport of pollution from China into the Seoul area. An example of this ongoing analysis is shown in Figure 5B.1. Figure 1a shows the  simulated model tracer concentrations interpolated to the time and location of surface air quality monitors in the Seoul area. The model includes three tracers for different regions in China: Beijing, Shandong and Shanghai. The results show two pronounced periods with influence of transport from China: Period 1 around May 16-18, and Period 2 from around 26-31 May. During Period 1, most influence is predicted from the Beijing and Shandong area with an average transport time of ~2 days, while during Period 2 the Shanghai tracer shows larger influence; specifically on May 27. The model estimates a transport time of ~3 days for this period.  While Period 2 had been identified as a transport period in previous studies, little attention had been given to Period 1. The strongest influence happened on May 17 (Figure 1b), just at the end of a period of strong dynamic forcing and before the onset of a multi-day stagnation period with weak synoptic flow over Korea and a persistent anticyclone. To confirm the modeled transport, we compare the WRF tracers to aircraft observations of CCl4, which has been shown to be a good tracer for China transport (Figure 1c). There is good agreement between enhancements in the China tracers and enhanced CCl4. This confirms that on 17 May transport from China was influencing the Seoul area and shows that most of the transport occurred at low altitudes. Further analysis will attempt to quantify the contribution of transported to local air pollution during this period.

WRF tracer concentrations
Figure 1: (a) Daily (8-18LT) average WRF tracer concentrations for Beijing, Shandong and Shanghai and their sum (“China”) for locations of air quality monitors in the Seoul metropolitan area. (b) Surface WRF China tracer on 17 May at 4 UTC (13 LT) with DC-8 aircraft track overlaid. Numbers indicate the hours into the flight. (c) Curtain plot of WRF China tracer along the DC-8 track. The black thick lines indicates the aircraft altitude and the thin black line indicates the modeled boundary layer height. Aircraft measurements of CCl4 are shown in red, with red arrows indicating periods of enhanced CCl4. Click for larger image.