Enrichment of atmospheric ammonia and ammonium in the north China plain

Abstract

Atmospheric ammonia and ammonium in PM10were measured at six sites (two suburban sites and four rural sites) in the North China Plain (NCP) between August 2006 and September 2009, i.e. for 3 years. The annual mean concentrations of ammonia and ammonium were 7.3–19.9 µ N m-3with an average of 12.8 µ N m-3and 5.6–13.1 µ N m-3with an average of 9.6 µ N m-3respectively, at the sampling sites. Both ammonia and ammonium concentrations were higher at the rural sites than at the suburban sites, highlighting the importance of agricultural sources for atmospheric ammonia and ammonium. Higher ammonia concentrations were observed in the nitrogen (N) fertilization seasons, indicating that ammonia emission from N fertilizer application was an important source of atmospheric ammonia in the NCP. Based on the measured ammonia and ammonium concentrations and their deposition velocities taken from literatures, the annual mean NHx(NH3plus NH4+) dry deposition rate was 25.6 kg N ha-1year-1among the six sampling sites. The high NHxconcentrations and dry deposition rates in the NCP indicated agricultural sources were a large contributor to air pollution, and should be taken into account in the control of regional air pollution.