Abstract
Abstract. A series of seven rainwater samples were collected in Wilmington, North Carolina USA originating from both continental and coastal storms and analyzed by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). This data set is unique in that it represents a detailed comparison of the molecular level composition of DOM in rainwater collected from distinctly different air mass back trajectories by FT-ICR MS. Approximately 25% of the roughly 2000 assigned CHO molecular formulas are unique to a single storm classification indicating the importance of air mass back trajectory on the composition of rainwater dissolved organic matter (DOM). Analysis of the unique molecular formula assignments highlighted distinct groupings of various bio- and geo-molecule classes with coastal storms containing unique formulas representative of lignin and cellulose-like formulas while continental storms had lipid-like formulas. A series of 18 distinct methylene oligomers were identified in coastal storms and 13 unique methylene oligomers in continental storms, suggesting oligomer formation is ubiquitous in rainwater albeit different for each storm classification. Oligomers of small acids and C3H4O2 were detected in both storm types indicating their processing may be similar in both back trajectories. Condensed aromatic hydrocarbons were detected in continental storms with phenol moieties that are not as oxidized as similar compounds detected in aquatic DOM.
Highlights
M lighted distinct groupings of various bio- and geo-molecule cant fraction of Dissolved organic matter (DOM) is chromophoric, suggesting this mateclasses with coastal storms containing unique formulas rep- rial plays a pivotal role in the wavelength dependent spectral resentative of lignin and cellulose-like formulas while conti- attenuation of solar radiHatiyondbryoalotmgoysphaenricdwaters
Oligomers of small tempts to characterize rainwater DOM have utilized a comacids and C3H4O2 were detected in both storm types indi- bination of spectroscopic and molecular level measurements cating their processing may be similar in both back trajectories
There have been significant advances made in the characterization of rainwater DOM and aerosol water-soluble organic carbon using ultra high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) (Nizkorodov et al, 2011; Altieri et al, 2009, 2012)
Summary
Rainwater samples were collected on the University of North Carolina Wilmington campus (34°13.9 N, 77°52.7 W) located approximately 8.5 km from the Atlantic Ocean. Four Aerochem Metrics (ACM) Model 301 Automatic Sensing Wet/Dry Precipitation Collectors were used to collect rain samples which housed a 4 L glass beaker placed within a HDPE plastic bucket. Rainwater samples were collected on an event basis and brought back to the laboratory less than 12 h after precipitation stopped. Real-time precipitation maps were used to define the end of specific rain events. Rainwater was filtered (0.2 μm pore size, polysulfone) and stored at 4 ◦C prior to analysis. All glassware used for rain collection, filtration apparatus and storage containers were baked at 450 ◦C in a muffle furnace for a minimum of 4 hours to remove organics prior to use. Meteorological data including rain amounts, rain duration, time of day, surface temperature and storm origin were recorded
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