Impacts of aerosol compositions on visibility impairment in Xi'an, China

Daily particle light scattering coefficient, PM2.5 mass and chemical composition were measured in Xi&#39;an from February to December 2009. Visibility was strongly affected by anthropogenic air pollution sources, resulting in an average visual range (VR) of 6.4 &plusmn; 4.5 km. The threshold PM2.5 mass concentration, corresponding to VR &lt;10 km, was &sim;88 &mu;g m&minus;3. The revised IMPROVE equation was applied to estimate chemical extinction (bext), which on average was &sim;15% lower than measured bext. PM2.5 ammonium sulfate was the largest contributor, accounting for &sim;40% of bext, followed by organic matter (&sim;24%), ammonium nitrate (&sim;23%), and elemental carbon (&sim;9%), with minor contributions from soil dust (&sim;3%), and NO2 (&sim;1%). High secondary inorganic aerosol contributions (i.e., SO42&minus; and NO3&minus;) were the main contributors for VR &lt;5 km. A Positive Matrix Factorization (PMF) solution to the Chemical Mass Balance (CMB) receptor model showed that coal combustion was the dominant factor, accounting for &sim;52% of the dry particle light scattering coefficient, followed by the engine exhaust factor (&sim;31%). Other factors included biomass burning (&sim;12%) and fugitive dust (&sim;5%).</p

Winter and Summer PM2.5 Chemical Compositions in Fourteen Chinese Cities

PM2.5 in 14 of China&#39;s large cities achieves high concentrations in both winter and summer with averages &gt; 100 mu g m(-3) being common occurrences. A grand average of 115 mu g m(-3) was found for all cities, with a minimum of 27 mu g m(-3) measured at Qingdao during summer and a maximum of 356 mu g m(-3) at Xi&#39;an during winter. Both primary and secondary PM2.5 are important contributors at all of the cities and during both winter and summer. While ammonium sulfate is a large contributor during both seasons, ammonium nitrate contributions are much larger during winter. Lead levels are still high in several cities, reaching an average of 1.68 mu g m(-3) in Xi&#39;an. High correlations of lead with arsenic and sulfate concentrations indicate that much of it derives from coal combustion, rather than leaded fuels, which were phased out by calendar year 2000. Although limited fugitive dust markers were available, scaling of iron by its ratios in source profiles shows similar to 20% of PM2.5 deriving from fugitive dust in most of the cities. Multipollutant control strategies will be needed that address incomplete combustion of coal and biomass, engine exhaust, and fugitive dust, as well as sulfur dioxide, oxides of nitrogen, and ammonia gaseous precursors for ammonium sulfate and ammonium nitrate.</p