Long-range transport of Asian dust and air pollutants to Taiwan

Dust storms and long-range transport of pollutants are major environmental concerns of Taiwan during the winter monsoon season when northeasterly winds prevail following passages of cold fronts. To quantify the impact on air quality, we develop an objective method to classify and study the long-range transport processes by examining the frontal passages in two representative years. We have found that there is about one frontal passage per week in winter and spring, consistent with the climatological average. The long-range transport events are classified into three types according to their degrees of impact on levels of dusts and air pollutants in Taiwan, namely dust storms (DS), long-range transport with pollutants (FP), and long-range transport of background air masses (13G). DS cases occurred 4.7% of the time over 14 months and had a large average PM10 concentration of 127.6 mu g m(-3) at Wan-Li station. FP cases occurred 1.9% of the time and the mean concentration of PM10 during the FP periods was about 85 mu g m(-3). BG cases happened 18.6% of the time and the mean concentration of PM10 was 32.8 mu g m(-3). Dust storms and air pollutants tend to be transported in different air parcels as evidenced by a lack of correlation between dust aerosols and air pollutants. The frequency of local pollution (LP) cases was 71.7% in winter and spring. The average PM10 concentration of LP cases at the Wan-Li station was 47.4 mu g m(-3). However, about one to two-thirds of the PM10 during LP cases can be attributed to the long-range transport. When this contribution is taken into account, we estimate that the contribution of long-range transport to PM10 abundance in northern Taiwan during winter and spring to be in the range of 50 % to 75 %.