A preliminary study of turbulent coherent structures and ozone air quality in Seoul using the WRF-CMAQ model at a 50 m grid spacing

Abstract

The effects of turbulent coherent structures on daytime ozone air quality in Seoul, South Korea are investigated through a case study using the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) model at a horizontal grid spacing of 50 m. In Seoul, sea breeze and convective structures develop in the daytime. Due to the different wind directions above and below the planetary boundary layer (PBL) top, eddies are formed at the PBL top when updrafts related to convective structures reach above the PBL top. Air at lower level, which has higher concentrations of O3 precursors and lower O3 concentration than air at upper level, is transported upward by convective structures and eddies at the PBL top. Some of the transported air reaches above the PBL top, resulting in the vigorous chemical production of O3 above the PBL top in the afternoon. An integrated process rate analysis is performed to examine the impacts of turbulent coherent structures on O3 concentration in detail. The chemical production of O3 generally appears in updraft areas except near the surface because O3 precursors at lower level are transported by updrafts. Below the height of ~1 km, the horizontal advection of air from other areas to updraft areas increases O3 concentration in updraft areas because O3 concentration in updraft areas is generally lower than that in other areas. Slightly above the PBL top, air with low O3 concentration diverges from updraft areas and air with high O3 concentration at upper level is transported downward by downdrafts around updraft areas.