Volume 9, No. 2, June 2009, Pages 277-289 PDF(329 KB)
Characterization of Atmospheric Ammonia over Xi’an, China
Jun-Ji Cao1,2, Ting Zhang1, Judith C. Chow3, John G. Watson3, Feng Wu1, Hua Li1
1 SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, China
2 Department of Environmental Science, Xi’an Jiaotong University, Xi’an, China
3 Division of Atmospheric Sciences, Desert of Research Institute, Reno, USA
Continuous measurements of atmospheric ammonia (NH3) between April 2006 and April 2007 were conducted at an urban site and a suburban site in Xi’an, northwest China. NH3 was collected using Ogawa passive samplers every sixth day. At the same time, NH4+ in fine particles was collected using battery-powered mini-volume samplers. The annual average concentrations of NH3 were 12.9 µg/m3 and 14.1 µg/m3, at the urban and suburban sites, respectively. The NH3 concentrations reached a maximum (~22.8-35.3 µg/m3) in June and July and were minimum (~3.0-4.7 µg/m3) in December, which was closely linked with NH3 volatilization under different ambient temperatures. The seasonal variation in NH3 was summer > spring > autumn > winter at both sites, which may be ascribed to the impact of biological emission sources such as agricultural activity. NH3 and NH4+ aerosol concentrations were weakly correlated, implying that gas-particle reactions are influenced by many factors such as sources, meteorology and removal. Average NH3/NH4+ ratios varied from 0.1 to 25.3, with an annual average of 4.0. High NH3 concentrations at Xi’an had a significant influence on atmospheric acidity and the formation of secondary NH4+ aerosol.
NH3; NH4+; Aerosol, Agricultural activity.