Pollution Properties of Water-Soluble Secondary Inorganic Ions in Atmospheric PM2.5 in the Pearl River Delta Region

• Published in: Aerosol and air quality research 2015, Vol.15 (5), p.1737-1747
• Main Authors: Yue, Dingli, Zhong, Liuju, Zhang, Tao, Shen, Jin, Zhou, Yan, Zeng, Limin, Dong, Huabin, Ye, Siqi
• Format: Article
• Language: English
• ISSN: 1680-8584; 2071-1409
• DOI: 10.4209/aaqr.2014.12.0333

Based on the online observation of PM 2.5 mass concentration, its water-soluble inorganic ions, and their gaseous precursors during August of 2013 to March of 2014 at the atmospheric supersite in the Pearl River Delta (PRD) region, the inter-action of the secondary compositions and their precursors was discussed, and the pollution properties of the secondary inorganic ions were revealed. During the whole measurement period, the average concentrations of SO 4 2– , NO 3 – and NH 4 + were 16.6 µg m –3 , 9.0 µg m –3 and 10.2 µg m –3 , respectively, with total contribution to PM 2.5 of 55.8%, indicating the significant role of secondary transformation in PM 2.5 pollution. The seasonal average total contributions of SO 4 2– , NO 3 – and NH 4 + to PM 2.5 varied from 46.0% to 64.3%, lowest in summer and highest in winter. The contributions of SO 4 2– and NH 4 + to PM 2.5 were relatively stable; while those of NO 3 – in different seasons were distinct, even dominating PM 2.5 in some pollution cases in winter. NH 3 was abundant with an annual average concentration of 15.2 µg m –3 , facilitating the neutralization of H 2 SO 4 and HNO 3 with the average [NH 4 + ]/(2[SO 4 2– ] + [NO 3 – ]) equivalent charge ratio of 1.1. The maximum daily peak concentration of HNO 3 was as high as 18.6 µg m –3 , providing an evidence for the strong oxidizing property of the atmosphere in the PRD region. The theoretical equilibrium constant (K e ) of NH 4 NO 3 is always lower than the observed concentration product (K m = [NH 3 ] × [HNO 3 ]) in spring and winter with higher HNO 3 concentrations; while in over 60% of the time during summer and autumn, mainly during daytime, K e was higher. In general, the strong oxidizing property and NH 3 played important roles in the fine particle pollution in the PRD region.