Case study of the Asian dust and pollutant event in spring 2006: Source, transport, and contribution to Taiwan

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Surface measurements and a regional dust model were used to analyze the source, transport, and contribution of a dust event transporting with aerosol pollutant over Taiwan from 16 to19 March, 2006. During the event, the hourly aerosol concentrations reached close to 400μgm−3 in northern Taiwan, and approximately 300μgm−3 in other areas of the island. Trajectory and regional dust models show that the dust event originated in eastern Mongolia and northern China, and the dust layer can descend from 2 to 3km in the source area to below 1.5km over Taiwan. On the other hand, model results show that pollution was transported near the surface from coastal China to Taiwan. During this dust event, polluted aerosol was first observed over northern Taiwan right after a frontal passage, and the concentration was strongly enhanced following the passage of the light rainfall 12h later. The descent of dusty air from the free troposphere lagged the arrival of polluted air by 7h, and was partially mixed with polluted aerosol when the transport decelerated over Taiwan.During the event, dust particles accounted for up to 60% of observed particulate matter less than 10μm (PM10) over Taiwan, but decreased to less than 35% for particulate matter less than 2.5μm (PM2.5) over most areas of the island. On the other hand, the long-range transport of non-dust aerosols, mainly anthropogenic pollutants, accounted for close to 30% of observed PM10 concentration in northern and western Taiwan prior to dust arrival, and the contribution of PM2.5 increased to close to 40% over the same areas. Local emission of aerosols accounted for less than 25% of PM10 concentrations in northern Taiwan, but was about 60% for PM2.5 in central and southern Taiwan because these areas are less influenced by long-range transport.