Characteristics of atmospheric ammonia over Beijing, China

• Main Authors: Z. Y. Meng, W. L. Lin, X. M. Jiang, P. Yan, Y. Wang, Y. M. Zhang, X. F. Jia, X. L. Yu
• Format: Article
• Language: English
• Published: Copernicus Publications 2011-06-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/11/6139/2011/acp-11-6139-2011.pdf
• ISSN: 1680-7316; 1680-7324

Continuous measurements of atmospheric ammonia (NH<sub>3</sub>) were conducted using Ogawa passive samplers from February 2008 to July 2010 at an urban site and from January 2007 to July 2010 at a rural site in Beijing, China. NH<sub>4</sub><sup>+</sup> in fine particles was also collected at the rural site during 2008–2009. The field comparison between the Ogawa passive samplers and an active analyzer for NH<sub>3</sub> conducted at the urban site assures the quality and accuracy of the measurements. The concentrations of NH<sub>3</sub> at the urban site ranged from 0.7 to 85.1 ppb, with the annual average of 18.5 ± 13.8 and 23.5 ± 18.0 ppb in 2008 and 2009, respectively. The NH<sub>3</sub> concentrations at the rural site were lower than those at urban site, and varied from 0.8 to 42.9 ppb, with the annual average of 4.5 ± 4.6, 6.6 ± 7.0 and 7.1 ± 3.5 ppb in 2007, 2008 and 2009, respectively. The data showed marked seasonal variations at both sites. The results emphasized traffic to be a significant source of NH<sub>3</sub> concentrations in winter in urban areas of Beijing. This was illustrated by the strong correlations of NH<sub>3</sub> with the traffic related pollutants (NO<sub>x</sub> and CO) and also by the bimodal diurnal cycle of NH<sub>3</sub> concentrations that was synchronized with traffic. Similar patterns were not observed during the summer, suggesting other non-traffic sources became more important. At the rural site, the daily NH<sub>4</sub><sup>+</sup> concentrations ranged from 0.10 to 36.53 μg m<sup>−3</sup>, with an average of 7.03 μg m<sup>−3</sup> from June 2008 to December 2009. Monthly NH<sub>3</sub> were significantly correlated with NH<sub>4</sub><sup>+</sup> concentrations. Average monthly NH<sub>3</sub>/NH<sub>4</sub><sup>+</sup> ratios varied from 0.13 to 2.28, with an average of 0.73. NH<sub>4</sub><sup>+</sup> in PM<sub>2.5</sub> was primarily associated with SO<sub>4</sub><sup>−2</sup> at the rural site.