Rapidly increasing ethanol concentrations in rainwater and air

Abstract Rainwater and gas phase ethanol concentrations increased approximately fourfold between 2010 and 2017 in Wilmington, NC, USA. This 8-year study demonstrates that the gas phase and rainwater concentrations of ethanol have risen due to increased production and use of ethanol as a biofuel. Rainwater ethanol concentrations are close to equilibrium with local atmospheric gas phase concentrations and have increased in proportion to increased air concentrations. Ethanol emissions are important because they impact the oxidizing capacity of the atmosphere due to the reactivity of the alcohol towards hydroxyl radical. Gas phase ethanol contributes to air pollution through oxidation to acetaldehyde, with subsequent production of ozone, and in high NOx regions production of peroxyacetyl nitrate (PAN). However, combustion of ethanol can also lower emissions of acetaldehyde precursors such as alkenes, suggesting that the potential impact of ethanol combustion is complex. The large increase in the concentration of ethanol in both the gas and condensed phases indicates that existing sinks are not sufficient to remove the excess alcohol being added to the atmosphere from biofuel use. This suggests that the projected growth of ethanol as a biofuel will result in considerable increases in atmospheric concentrations within the next few years with direct ramifications on a host of fundamentally important atmospheric processes.