Asian dust and pollution transport-A comprehensive observation in the downwind Taiwan in 2006

摘要

This study analyzed the air pollution episode which affected Taiwan on March 19 and 20, 2006, an event confirmed to have been caused by Asian dust (AD). During this AD event, the maximum hourly values of PM_(2.5) and PM(2.5-10) particles at 136 and 218 μg m~(-3), respectively, were recorded at the Taipei aerosol supersite (TAS) located in northern Taiwan. Moreover, of Taiwan's 74 air quality monitoring stations, 65 (on March 19) and 29 stations (March 20) recorded daily average concentrations of PM_(10) which exceeded Taiwan's air quality standard of 125 μg m~(-3). This AD event not only greatly increased the PM_(2.5) and PM_(2.5-10) concentrations, but the gaseous pollutants transported by the northeast monsoon were predicted to adversely affect Taiwan as well. In addition to ground measurements, an aerosol layer was detected in Taipei, the thickness of which was verified to be about 800 m through the light detection and ranging (LIDAR) method. During the AD-affected period (defined as the situation where the concentration of PM_(2.5-10) maintains a high value), the black carbon (BC) fraction of PM_(2.5) was reduced from 15.7 to 5.6%; sulfate fraction of PM_(2.5) increased from 7.1 to 19.8%; and the nitrate fraction of PM_(2.5) was reduced slightly from 10.3 to 8.1% at the TAS site. Moreover, the particles' number size spectra showed a decrease in the amount of particles with a diameter of less than 200 nm, indicating that the rise of the concentration of PM_(2.5) increased along with the increase of PM_(2.5) particles with diameters larger than 200 nm. This study demonstrates that anthropogenic pollutants from the Asian mainland including nitrates, sulfates, BC, gaseous pollutants (CO, SO_2, and O_3), and other fractions of fine particles, would influence the downwind regions as the AD is transported.