Field investigation of water soluble ionic species in aerosols and the formation of fine sulfate and nitrate in the atmosphere.

摘要

Water soluble ionic species in PM2.5 play an important role in the climate forcing, heterogeneous chemistry and human health. In this study, the data of both one hour and twenty-four hour water soluble ions were used for interpreting the behaviors of ion species in the atmosphere. This study was conducted in the megacities of China which has long been known for its severe air pollution. In addition, there is limited knowledge on the distribution of aerosols in suburban and/or rural areas and on the formation of secondary aerosols in China. Thus, this study is important for the understanding of ion species as well as the current air pollution situation in China.;The comparison of the AIM with another semi-continuous sulfate and nitrate instruments as well as the filter analysis have shown that the two methods had a good overall correlation for sulfate and nitrate, but showed discrepancies in absolute concentrations.;The variations of the PM2.5 mass and water soluble ion species collected in different parts of China were presented. Analysis of the dataset suggested that meteorological and chemical factors contributed to the high PM2.5 aerosol concentrations. The diurnal profiles of sulfate and nitrate were different at different places. Sulfate, nitrate and ammonium were generally the major components of the water soluble ions.;25--67% of SO2 were found to have been converted to sulfate in seven urban pollution plumes examined in Beijing. An examination of SO 2 versus total sulfur under different humidity indicated that the conversion of SO2 was most efficient under humid conditions in Beijing. For the nitrate formation pathways, Lanzhou and Guangzhou were mainly through gas-phase homogeneous reaction between ammonia and nitric acid, while Beijing and Shanghai were through heterogeneous hydrolysis of N2O 5.;The visibility problem in Beijing was very serious. Results suggested that fine particulates were the major visibility reducing aerosol components in the polluted atmosphere in Beijing. Furthermore, ammonium sulfate and ammonium nitrate contributed to the high fraction of the light extinction, especially during the episode days. This suggested that water soluble ions played a significant role in the visibility impairment in the Beijing area.