Characteristics, Origins, and Atmospheric Processes of Amines in Fine Aerosol Particles in Winter in China

Amines affect particle formation, aerosol acidity, nitrogen cycle, and climate change. However, little is known about the temporal and spatial differences in the composition, source, and formation process of amines in fine particulate matter (PM2.5) in different regions of China. Seven amines (amine salts) were investigated in PM2.5 collected in the Yangtze River Delta (YRD, Shanghai and Nanjing), Pearl River Delta (PRD, Guangzhou), northern China (Xi'an and Haerbin), and background (Puding) areas in winter 2017-2018. Methylamine was the dominant amine species at the YRD, northern China, and background sites, while diethylamine dominated at the PRD site; moreover, the mass concentration and fraction of diethylamine were the lowest at the background site. These results could be attributed to changes in sources and atmospheric processes. Further, coal combustion and biomass burning were found to be important contributors of amines in northern cities in winter. The contribution of biomass and coal combustion to amines was weakened in other urban sites. In contrast, the amine abundance at the background site was largely controlled by biogenic sources. Acid-base chemistry and displacement mechanism were tightly associated with the formation of amine salts at all sites. In particular, the atmospheric degradation of amines by hydroxyl radical (center dot OH) was significant at the Nanjing, Guangzhou, Xi'an, and Haerbin sites. The insignificant photochemical degradation of amines at the Shanghai and background sites can be explained by differentiated amine sources, meteorological conditions, and center dot OH levels. Overall, our findings deepen the understanding of the origins and atmospheric processes of amines. Plain Language Summary Concentrations, compositions, potential sources, and major atmospheric processes of amines in winter PM2.5 in different regions of China were systematically investigated for the first time. The concentrations and compositions of amines in PM2.5 showed significant spatial differences, with the dominance of diethylamine at the Guangzhou site and the dominance of methylamine at other sites (Nanjing, Shanghai, Xi'an, Haerbin, and background sites). The influence of coal combustion associated with heating and industry was a typical feature that distinguishes the difference of amine sources between the coastal and northern areas. Moreover, the overall amine abundance at the background site was largely controlled by biogenic sources. Acid-base chemistry and displacement mechanism were tightly associated with the formation of amine salts in PM2.5 at all sites. The atmospheric processes related to center dot OH exerted a significant impact on the removal of amines at the Nanjing, Guangzhou, Xi'an, and Haerbin sites. The insignificant photochemical degradation of amines in the Shanghai and background areas was associated with varied amine sources, meteorological conditions, and center dot OH levels. The overall results improve the current understanding on the temporal and spatial variations in the composition, source, and atmospheric process of amines in China.