Asian dust over northern China and its impact on the downstream aerosol chemistry in 2004

TSP and PM2.5 aerosol particles were synchronously sampled at six sites along the transport pathway of dust storms from desert regions to coastal areas in the spring of 2004 to investigate the regional characteristics of Asian dust and its impact on aerosol chemistry over northern China. Factor analysis of daily PM10 concentrations in 17 cities showed that northern China can be basically divided into five regions: (1) Northern Dust Region, (2) Northeastern Dust Region, (3) Western Dust Region, (4) Inland Passing Region, and (5) Coastal Region. Northern Dust Region was characterized by a high content of Ca. Northeastern Dust Region was a relatively clean area with a low concentration of pollutants and secondary ions in comparison to other regions. Inland Passing Region and Coastal Region showed high concentrations of anthropogenic pollutants. The impact of Asian dust on aerosol chemistry decreased in the order Yulin/Duolun > Beijing > Qingdao/Shanghai as transport distance increased. The ratio of Ca/Al, which showed significant differences in different regions over northern China, is suggested to be a tracer to identify the sources of dust storms. Asian dust either mixes pollutants on the pathway and carries them to the downwind regions or dilutes the pollutants over northern China, which affects the aerosol composition more in coarse particles in those areas near source regions and more in fine particles in downwind areas. The ratio of NO3-/SO42- during dust storms was significantly reduced and the lowest generally appeared after the peak of dust. Our results showed that Asian dust plays a critical role in buffering the acidity of aerosols over northern China by a potential increase of similar to 1 unit pH for the aerosol particles in spring.