Chemical Characteristics of Particulate Matter during a Heavy Dust Episode in a Coastal City, Xiamen, 2010
Xiamen, as a southeastern coastal city, is hardly affected by dust storms (DSs) sourced from the arid and semiarid areas in North or Northwestern China in spring. Unfortunately, during 21–23 March, 2010, the heaviest DS that had been recorded in past 50 years affected air quality seriously. Continuous particulate matter monitor was employed for the observation of PM2.5 (aerodynamic diameter less than 2.5 μm) and PM10 (aerodynamic diameter less than 10 μm) during 20–24 March 2010. Total suspended particulate (TSP) samples during this episode were also collected and their characteristics of element species and water-soluble ions were illustrated to characterize the heavy pollution in Xiamen. The DS peaked on 21 March, with the highest concentrations of 454.51 μg/m3 and 990.24 μg/m3 for PM2.5 and PM10, respectively. The variations of ratio for PM2.5/PM10 indicated that PM10 was the main particles that were influenced by DS. The higher ratios (DS/Non dust days) of Al, Fe, Mg, Mn, and Ba were over 5.0, which are primarily from a soil. However, the ratios of Zn, V, As, Ti, and Cr, mainly from anthropogenic sources, had a range of 1.3 to 3.4. These results suggested that the soil-sourced species made more contribution to DS particles compared to the anthropogenic species. The mass fractions of water-soluble ions in TSP indicated that the concentrations of K+, Ca2+, Mg2+, F-, NO2-, and NO3- were evidently higher in DS samples than those of non-DS samples. The compositions of ions in dust aerosols showed that the multi-sources of aerosol were ubiquitous during the dust episode. The highest concentrations of sulfate and nitrate occurred in the day when dust ended in Xiamen, which demonstrated the formation of secondary pollutants from dust during the long-range transport, as well as from local environmental pollution.
