Atmos. Chem. Phys., 10, 9487–9503, 2010 www.atmos-chem-phys.net/10/9487/2010/ doi:10.5194/acp-10-9487-2010 © Author(s) 2010. CC Attribution 3.0 License. Atmospheric Chemistry and Physics Occurrence of gas phase ammonia in the area of Beijing (China) A. Ianniello 1 , F. Spataro 1 , G. Esposito 1 , I. Allegrini 1 , E. Rantica 1 , M. P. Ancora 1 , M. Hu 2 , and T. Zhu 2 1 CNR – Institute of Atmospheric Pollution Research, Via Salaria Km 29.3, CP10, 00015 Monterotondo S., Rome, Italy 2 State Key Joint Laboratory for Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China Received: 6 May 2010 – Published in Atmos. Chem. Phys. Discuss.: 9 June 2010 Revised: 10 September 2010 – Accepted: 26 September 2010 – Published: 7 October 2010 Abstract. The atmospheric concentrations of gaseous am- monia have been measured during two field campaigns in the winter and in the summer of 2007 at Beijing (China). These measurements were carried out by means of diffusion annu- lar denuders coated with phosphorous acid. The results were discussed from the standpoint of temporal and diurnal vari- ations and meteorological effects. The daily average NH 3 concentrations were in the range of 0.20–44.38 μg/m 3 and showed regular temporal variations with higher concentra- tions during summer and with lower during winter. The tem- poral trends seemed to be largely affected by air temperature because of agricultural sources. No diurnal variability was observed for gaseous NH 3 levels in both winter and sum- mer seasons. The highest ammonia value of 105.67 μg/m 3 was measured in the early morning during the summer pe- riod when stable atmospheric conditions occurred. The di- urnal winter and summer trends of ammonia showed a weak dependence on the air temperature and they were affected nearly by wind direction suggesting regional and local source influences. Ammonia was also correlated with the atmo- spheric mixing in the boundary layer, and, with NO x , CO and PM 2.5 air concentrations supporting the hypothesis that the traffic may be also an important source of ammonia in Beijing. 1 Introduction Gaseous ammonia (NH 3 ) is the third most abundant nitrogen containing compound and is the primary alkaline trace gas in the atmosphere. The importance of ammonia in urban areas is related to its role as a precursor for secondary aerosols Correspondence to: A. Ianniello (ianniello@iia.cnr.it) (Erisman and Schaap, 2004). It neutralizes atmospheric acids such as nitric acid (HNO 3 ), hydrochloric acid (HCl) and sulphuric acid (H 2 SO 4 ), formed by oxidation of nitro- gen oxides (NO x ) and sulphur dioxide (SO 2 ), respectively (Krupa, 2003), thereby affecting the acidity of cloud water and aerosols (Heeb et al., 2006; Roelle and Aneja, 2002). The reaction rates for NH 3 depend on the acid concentra- tion, humidity and temperature. The main chemical sink for ammonia in the atmosphere is the reaction with H 2 SO 4 , yielding ammonium sulphate [(NH 4 ) 2 SO 4 ] and ammonium bisulphate [NH 4 HSO 4 ] salts. Reactions with HNO 3 and HCl yield ammonium nitrate (NH 4 NO 3 ) and ammonium chloride (NH 4 Cl) salts in particulate phase. These NH + 4 aerosols con- tribute significantly to fine particle mass (size <2.5 μm) and have implications for human health (Brunekreef and Holgate, 2002). They limit atmospheric visibility and alter global ra- diation budgets (Horvat, 1992; Sutton et al., 1994). The most recent consideration for NH 3 emissions on the global scale is linked to climate change based on its abil- ity to form PM 2.5 , specifically ammonium sulphates. These aerosols can possibly increase the earth’s albedo. Particles can either backscatter UV and visible radiation directly, re- ducing the amount that reaches the earth’s surface, or indi- rectly by increasing cloud cover due to increased numbers of cloud condensation nuclei, particles that give rise to cloud formation (Sutton et al., 2004). NH 3 has a relatively short residence time of about 1 to 5 d. When airborne, it is ei- ther readily converted to ammonium aerosols, due to their ex- tended lifetime (about 1–15 d), these particles may be trans- ported far from the pollutant sources (Aneja et al., 2001; Krupa, 2003) causing effects to sensitive ecosystems with consequent changes in soil, plant and animal communities (Sutton et al., 1993; Fangmeier et al., 1994). In fact, after deposition, NH + 4 aerosols can contribute to acidification and eutrophication of these habitats. Thus, since NH 3 is either readily converted to NH + 4 or subjected to dry deposition, high Published by Copernicus Publications on behalf of the European Geosciences Union.