摘要 :
occurred in summer and autumn,and there was evidence for the formation of ammonium bisulfate in TSP,ammonium sulfate in PM_(2.5),and ammonium nitrate in both fractions.Comparisons with the results of prior studies indicate that po...
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occurred in summer and autumn,and there was evidence for the formation of ammonium bisulfate in TSP,ammonium sulfate in PM_(2.5),and ammonium nitrate in both fractions.Comparisons with the results of prior studies indicate that pollution controls in Xi'an have reduced the levels of air pollution over the past 10 yr.The SO_4~(2-) concentration during the heating season in 2006 was only about one-eighth of that in 1996,and NH_4~+ decreased to one-ninth of that in 1996.Seasonal variations in the NO~(2-)/SO_4~(2-)ratio are different than the patterns observed 10 yr ago,suggesting that emission sources have changed,with those from motor vehicles becoming increasingly important.
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