Determination of Wet Deposition Ethanol Concentration in the Eastern US and South TX
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This study represents the first comprehensive analysis of wet deposition ethanol in the Eastern US and South Texas to better comprehend how ethanol emissions are affecting atmospheric ethanol concentrations. Ethanol concentrations measured in 204 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 and concentrations measured in 48 rain events in South Texas during the same time period ranged from below the detection limit to 13195 nM. The volume weighted average ethanol concentration of AIRMoN samples ranged from 208 nM to 1017 nM while the volume weighted average ethanol concentration in South Texas was 1177 nM. Adding the five AIRMoN data to the previous empirical-based global wet deposition flux estimated by using data from 12 sites globally, the global wet deposition ethanol flux was estimated to be 2.7 ± 1.3 Tg/yr. No significant correlation + - 2- - 2+ + 2+ + was observed between ethanol and any analytes (NH4 , Cl, SO4 , NO3 , Ca , Na , Mg , K , PO43- and H+) in almost all sites in the study, likely due to the difference in atmospheric residence time and emission sources. When investigating AIRMoN data as a whole, a significant correlation was observed between ethanol and chloride and ethanol and sodium ion concentration, suggesting common inputs from forest or marine sources. Significant seasonal variations of ethanol were not observed for any sites, which suggest a continuous emission of ethanol to the atmosphere. Anthropogenic and biogenic (with and without C4 plants) contributions to atmospheric ethanol were estimated using ISOERROR and SIAR isotope mixing models. Excluding C4 plants in the models, our results suggest that the greater fraction of ethanol in South Texas (ISOERROR: 70.6 ± 12.8%; SIAR: 68.4 ± 12.7%) and NY67 (ISOERROR: 66.1 ± 11.9%; SIAR: 63.4 ± 12.9%) was emitted from anthropogenic sources; the contribution of biogenic (ISOERROR: 49.6%; SIAR: 52.2 ± 12.7%) and anthropogenic (ISOERROR: 50.4%; SIAR: 47.8 ± 12.7%) sources was equivalent in WV99 while the biogenic (ISOERROR: 63.2 ± 8.3%; SIAR: 60.4 ± 16.5%) sources contribution was dominant in TN00. Including C4 plants in the models, our results suggest that the greater fraction of ethanol in South Texas (ISOERROR: 58.1 ± 14.8%; SIAR: 56.9 ± 16.0%) and NY67 (ISOERROR: 63.4 ± 12.6%; SIAR: 58.3 ± 19.5%) was emitted from anthropogenic sources; the contribution of biogenic sources was dominant in TN00 (ISOERROR 74.2 ± 10.1%; SIAR: 67.2 ± 18.3%) and WV99 (ISOERROR 70.7%; SIAR: 67.8 ± 14.8%). Therefore, as the distribution of C3 and C4 plants varies from site to site, this study suggests that it is important to consider the types of plants around each site before assigning the representative endmember value for biogenic sources. Results of this study are important as it provides atmospheric scientists, environmental chemists and policy makers with a baseline of atmospheric ethanol concentration in order to help determine the efficacy of future ethanol fuel use and to help quantify the wet deposition ethanol sink. As ethanol fuel consumption and thereby emissions are increasing globally, it is important to understand the magnitude of all ethanol sources and sinks and their impacts in the atmosphere.