The role of boundary layer schemes in meteorological and air quality simulations of the Taiwan area

Adequate air quality modeling is reliant on accurate meteorological simulations especially in the planetary boundary layer (PBL). To understand how the boundary layer processes affect the mixing and transport of air pollutants, the sensitivity of Weather Research Forecasting (WRF) model with different PBL schemes (YSU and MYJ) is utilized. Community Multiscale Air Quality (CMAQ) modeling system is performed subsequently to study the effects of the PBL physical processes on the meteorological and air quality simulations. A comparison is made of two distinct atmospheric conditions. Case 1 considers the influence of the Asian continental outflow where air pollutants carried by long-range transport (LRT) to Taiwan. The variation in ozone (O3) concentration between the two sensitivity runs is mainly caused by the PBL height difference with WRF–MYJ predicts much deeper PBL height near the frontal low-pressure region than does the WRF–YSU. Case 2 is associated with the land-sea breeze flow. In this situation O3 is locally produced from the western side of the country where major metropolitan cities and highways are located. Distinctions in O3 are caused by difference in the strength of the land-sea breeze flow between the two runs. At night the WRF–YSU predicts a weaker offshore land breeze than does the WRF–MYJ near the western coastline. During the day, the WRF–YSU predicts a stronger sea breeze near the offshore area than does the WRF–MYJ, while over the landside, the WRF–YSU predicts a lower wind speed than does the WRF–MYJ.