title: Summertime ambient ammonia and its effects on ammonium aerosol in urban Beijing, China.
abstract: To improve the understanding of NH3variation in urban Beijing, high temporal resolution (1-min averaged) NH3data derived during the summer of 2009 were analyzed. The results indicated that after rain there was generally an increase in NH3concentration. The analysis of the 1-min data revealed that a weak but significant linear correlation existed between NH3and NOxin August, indicating a connection between NH3concentrations and traffic levels during summer. This was further supported by peak NH3levels approximately coinciding with morning rush hours. The daily NH3concentrations were weakly correlated with NH4+concentrations, suggesting that NH3played an important precursor role in NH4+in PM2.5formation. The mean mass ratio of NH3/NHxwas 0.76±0.13. This revealed that NHx(NH3+NH4+) was influenced by local sources during the summer period and that NH3dry deposition could contribute substantially to NHxdeposition. A high temperature, relative humidity, and degree of oxidization could increase photochemical reactions and aqueous processing, having the important effect of SO2to SO42-and NH3to NH4+conversion in summer. The back trajectory analysis indicates that the transport of air masses from the North China Plain region contributed to the atmospheric NH3and NH4+aerosol variations in Beijing.
authors.affiliation: State Key Laboratory of Severe Weather & Key Laboratory for Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China. Electronic address: mengzy@camscma.cn.
authors.forename: Zhaoyang
authors.initials: Z
authors.lastname: Meng
authors.affiliation: CMA Meteorological Observation Centre, Beijing 100081, China.
authors.forename: Weili
authors.initials: W
authors.lastname: Lin
authors.affiliation: Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China.
authors.forename: Renjian
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Han
authors.affiliation: CMA Meteorological Observation Centre, Beijing 100081, China.
authors.forename: Xiaofang
authors.initials: X
authors.lastname: Jia
keywords: Ambient ammonia; Ammonium in PM(2.5) particulates; Gas-to-particle conversion; Urban Beijing