Wet deposition ethanol concentration at US atmospheric integrated research monitoring network (AIRMoN) sites

Ethanol concentrations measured in 178 event-based wet deposition samples collected at five Atmospheric Integrated Research Monitoring Network (AIRMoN) sites in the Eastern US between February 2018 to January 2019 ranged from below the detection limit of 19 nM to 4160 nM. The volume weighted average ethanol concentration at each site ranged from 237 nM to 1375 nM. No significant correlation was observed between ethanol and any analytes (NH₄⁺, Cl⁻, SO₄²⁻, NO₃⁻, Ca²⁺, Na⁺, Mg²⁺, K⁺, PO₄³⁻ and H⁺) at all sites in the study, likely due to differences in atmospheric residence time and emission sources. Significant seasonal variations of ethanol were not observed for any sites, however notably higher concentrations in the winter vs. summer and growing vs. nongrowing seasons suggest photochemical dynamics play a substantial role in seasonal atmospheric concentrations. The AIRMoN concentrations were combined with previous measured ethanol wet deposition data to produce an updated empirical-based global wet deposition ethanol flux of 3.7 ± 1.8 Tg/yr (n = 1051). The carbon isotopic composition of a subset of samples ranged from −25.8 to −15.7‰ with an average of (−20.4 ± 4.0‰, n = 6). Isotope mixing model results indicate an approximately equivalent contribution of biogenic (55.2 ± 14.4%) and anthropogenic (44.8 ± 14.4%) sources of ethanol to the atmosphere over all collections sites. Results provide atmospheric scientists, environmental chemists and policy makers with baseline U.S. atmospheric ethanol concentrations in order to help determine the impact of future ethanol fuel production and to help quantify the wet deposition ethanol sink.