Impact of tropical cyclone track change on regional air quality.

There has been an increase in tropical cyclones (TCs) in the western North Pacific (WNP) that traverse with a northward recurving track towards East Asia and a decrease in TC tracks entering the South China Sea (SCS) in the past few decades. To investigate the potential impact of the prevailing TC track change on Hong Kong air quality, an analysis has been carried out based on historical data (1991 to 2010) of TC tracks and air quality. Compared to TCs in other regions, TCs in the vicinity of Taiwan (Region 2, R2) have the greatest impact on Hong Kong air quality due to regional transport of air pollutants from the highly industrialized Pearl River Delta (PRD). In the last twenty years, the number of days with TCs in R2 (May to October) has increased by 45% from 111days in the period 1991-2000 to 161days in 2001-2010, during which there was an increase in yearly TC-related pollution episodes of approximately 3 episodes per year in Hong Kong. The enhancement of mean O concentration due to TCs in R2 is reported as 82% (~50.8μg/m at a rural station) and 58% (~16.8μg/m at an urban station) higher than the summer averages. A similar enhancement is also observed for PM (called RSP) and SO with an average of 70% (i.e., 22.2μg/m) and 100% (i.e., 15.2μg/m) increases, respectively. Overall, the 20years of historical data show that the O concentrations on the TC-affected days are increasing at the estimated rates of 0.5μg/m and 2.6μg/m per year, respectively, in the urban and remote areas, which are significantly higher than the increase of 0.3μg/m and 0.4μg/m per year in the average summer concentrations.