Removal of atmospheric ethanol by wet deposition

The global wet deposition flux of ethanol is estimated to be 2.4 +/- 1.6 Tg/yr with a conservative range of 0.2- 4.6 Tg/yr based upon analyses of 219 wet deposition samples collected at 12 locations globally. This estimate calculated by using observed wet deposition ethanol concentrations is in agreement with previous models (1.4- 5 Tg/yr) predicting the wet deposition sink using Henry's law coefficients and atmospheric ethanol concentrations. Wet deposition is estimated to remove between 6 and 17% of the total ethanol emitted to the atmosphere on an annual basis. The concentration of ethanol in marine rain (25 +/- 6 nM) is an order of magnitude less than in the majority of terrestrial rains (345 +/- 280 nM). Terrestrial rain samples collected in locations impacted by high local sources of biofuel usage and locations downwind from ethanol distilleries were an order of magnitude higher in ethanol concentration (3090 +/- 448 nM) compared to rain collected in terrestrial locations not impacted by these sources. These results indicate that wet deposition of ethanol is heavily influenced by local sources. Results of this study are important because they suggest that as biofuel production and usage increase, the concentration of ethanol in the atmosphere will increase as well the wet deposition flux. Additional research constraining the sources, sinks, and atmospheric impacts of ethanol is necessary to better assist in the debate as whether or not to increase consumption of the alcohol as a biofuel.