Summertime ambient ammonia and ammonium aerosol in Beijing urban area, China

摘要

The mean hourly concentrations of NH_3, SO_2 and NO_x were 39.2, 4.28 and 32.5 ppb, respectively, during summer 2009. The NH_4~+, SO_4~(2-), NO_3~- and Cl~- in PM_(2.5) were 11.0, 23.5,12.8 and 0.29 μg/m~3 in July 2009. The contribution from traffic was observed in the summer, which illustrated by a weak but significant correlation existed between NH_3 and NO_x and NH_3 peak in morning rush hours. At Beijing urban site, NH_3 is primarily in the gas phase during summer season, indicating a system in which NH_x is influenced by local NH_3 sources and dry deposition of NH_3 is likely a significant component of NH_x deposition. The elevated levels of NH_3 have an important influence on the basic characteristics of inorganic PM_(2.5). The air masses from the North China Plain region contain the highest concentration of ammonia, suggesting a potential contribution of air transport to our measurements. Meanwhile, the most frequent southeast airflow is connected with high secondary water-soluble ions concentrations during summertime.