Abstract
Abstract. Wet deposition is an important removal mechanism for atmospheric organic matter, and a potentially important input for receiving ecosystems, yet less than 50% of rainwater organic matter is considered chemically characterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Elemental compositions of 552 unique molecular species were determined in the mass range 50–500 Da in the rainwater. Four main groups of organic compounds were identified: compounds containing carbon, hydrogen, and oxygen (CHO) only, sulfur (S) containing CHOS compounds, nitrogen (N) containing CHON compounds, and S- and N- containing CHONS compounds. Organic acids commonly identified in precipitation were detected in the rainwater. Within the four main groups of compounds detected in the rainwater, oligomers, organosulfates, and nitrooxy-organosulfates were assigned based on elemental formula comparisons. The majority of the compounds identified are products of atmospheric reactions and are known contributors to secondary organic aerosol (SOA) formed from gas phase, aerosol phase, and in-cloud reactions in the atmosphere. It is suggested that the large uncharacterized component of SOA is the main contributor to the large uncharacterized component of rainwater organic matter.
Highlights
Precipitation is an efficient removal mechanism for atmospheric organic matter, which is a mixture of organic compounds that can influence climate, air quality, and ecosystem health
The contribution of organic acids to total Dissolved organic carbon (DOC) ranges from only 14–36%, with other known compound classes contributing
A large percentage of the uncharacterized rainwater dissolved organic matter (DOM) has been attributed to macromolecular organic matter like that found in atmospheric aerosols, fog water and cloud water (Zappoli et al, 1999; Krivacsy et al, 2000; Feng and Moller, 2004; Likens, 1983)
Summary
Precipitation is an efficient removal mechanism for atmospheric organic matter, which is a mixture of organic compounds that can influence climate, air quality, and ecosystem health. A large percentage of the uncharacterized rainwater DOM has been attributed to macromolecular organic matter like that found in atmospheric aerosols, fog water and cloud water (Zappoli et al, 1999; Krivacsy et al, 2000; Feng and Moller, 2004; Likens, 1983). Much of this macromolecular material has been termed humic like substances (HULIS) because of properties similar to terrestrial and aquatic humic and fulvic acids (Graber and Rudich, 2006).
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