Paper Title
Orographic Effect on Air Quality in Taiwan: An Island with Complex Terrain

Abstract
Weather types and orography are important factors on air quality, especially in island which has complex terrain and amount of emission. In this study, air quality monitoring data of all regular stations of Taiwan Environmental Protection Administration (TEPA) and Weather Research and Forecasting model (WRF) were used to examine the PM2.5 events during 2013-2017. The spatial distribution of air pollutants correlated with terrain and environmental flow were checked to understand the orographic impact. The most frequently weather type dominates the air quality of Taiwan, continental high pressure, was analyzed at first, it found that the high-pressure center moved to more northern (base region is between 30-35 N) instead of the historical position year by year during the winter. Additionally, there were 135 episodes occurred when the prevailing wind direction was northern-east, when the air pollutants accumulated in leeside and southern areas of this island. In these cases, the winter northern-east wind passed the high mountain terrain (Central Mountain Range, CMR) and split in lower atmosphere. The split flow formed leeside vortices and determined the accumulation areas, the results indicate environmental flow wind interacted with the terrain is one of the important keys in air quality issues of Taiwan. Keywords - Orography, WRF, Air Quality, Leeside Vortex