Importance of gas-particle partitioning of ammonia in haze formation in the rural agricultural environment

Xu, Jian; Chen, Jia; Zhao, Na; Wang, Guochen; Yu, Guangyuan; Li, Hao; Huo, Juntao; Lin, Yanfen; Fu, Qingyan; Guo, Hongyu; Deng, Congrui; Lee, Shan-Hu; Chen, Jianmin; Huang, Kan

Ammonia in the atmosphere is essential for the formation of fine particles that impact air quality and climate. Despite extensive prior research to disentangle the relationship between ammonia and haze pollution, the role of ammonia in haze formation in high ammonia-emitting regions is still not well understood. Aiming to better understand secondary inorganic aerosol (sulfate, nitrate, ammonium – SNA) formation mechanisms under high-ammonia conditions, 1-year hourly measurement of water-soluble inorganic species (gas and particle) was conducted at a rural supersite in Shanghai. Exceedingly high levels of agricultural ammonia, constantly around 30 inline-formulaµg minline-formula−3, were observed. We find that gas-particle partitioning of ammonia (inline-formulaεinline-formula M4inlinescrollmathml chem ( normal NH normal 4 + ) 31pt15ptsvg-formulamathimg91d49abe6d72fd4b0e5a1f1b4385a2d5 acp-20-7259-2020-ie00001.svg31pt15ptacp-20-7259-2020-ie00001.png ), as opposed to ammonia concentrations, plays a critical role in SNA formation during the haze period. From an assessment of the effects of various parameters, including temperature (inline-formulaT), aerosol water content (AWC), aerosol pH, and activity coefficient, it seems that AWC plays predominant regulating roles for inline-formulaεinline-formula M7inlinescrollmathml chem ( normal NH normal 4 + ) 31pt15ptsvg-formulamathimg459544f7453cdb23fbb6134fb577afe9 acp-20-7259-2020-ie00002.svg31pt15ptacp-20-7259-2020-ie00002.png . We propose a self-amplifying feedback mechanism associated with inline-formulaεinline-formula M9inlinescrollmathml chem ( normal NH normal 4 + ) 31pt15ptsvg-formulamathimgb3dc5eafd33a1d448ae2e5721d3e9b65 acp-20-7259-2020-ie00003.svg31pt15ptacp-20-7259-2020-ie00003.png for the formation of SNA, which is consistent with diurnal variations in inline-formulaεinline-formula M11inlinescrollmathml chem ( normal NH normal 4 + ) 31pt15ptsvg-formulamathimg9035a82d717fef1a3b8f58fb0723e83a acp-20-7259-2020-ie00004.svg31pt15ptacp-20-7259-2020-ie00004.png , AWC, and SNA. Our results imply that a reduction in ammonia emissions alone may not reduce SNA effectively, at least at rural agricultural sites in China.

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Xu, Jian / Chen, Jia / Zhao, Na / et al: Importance of gas-particle partitioning of ammonia in haze formation in the rural agricultural environment. 2020. Copernicus Publications.

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