Molecular level characteristics and sources of rainwater water-soluble organic matter in different regions of China by FT-ICR MS

Abstract

Rainwater water-soluble organic matter (WSOM) constitutes a complex mixture that holds a pivotal role in biogeochemical cycles and climate change. Understanding its chemical composition helps better to reveal its atmospheric behavior. In this study, rainwater samples were collected from three Chinese cities to explore their WSOM molecular composition and sources. These rainwater samples contained significant amounts of both natural and anthropogenic WSOM owing to diverse environmental settings and extensive human activities. Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was employed to analyze the molecular diversity of rainwater WSOM. A total of 1684, 2024, and 1104 molecular formulas were identified in rainwater WSOM from Anshan, Guangzhou, and Nanjing, China, respectively. The results reveled that sulfur-containing compounds (including CHOS and CHONS) dominated the rainwater WSOM in Anshan (74.9 %), with a notable presence of nitrooxy-organosulfates. In contrast, in Guangzhou, typical biogenic derivatives of CHO compounds contributed more to the rainwater WSOM (50.5 %). In Nanjing, the sulfur-containing compounds and CHO compounds were primarily composed of nitrooxy-organosulfates and saturated fatty acids, respectively, comprising 48.6 % and 43.8 % of the rainwater WSOM. On the whole, rainwater WSOM mainly originated from industrial emissions, secondary generation, biomass burning, and vehicle emissions.