US ethanol fuel consumption has increased exponentially over the last two decades as part of a movement to reduce greenhouse gas emissions and become more fuel independent. US annual renewable fuel production is ~17 billion gallons and is targeted to increase to 36 billion by 2022 according to the renewable fuel standard. Regardless of the technology or feedstock used to produce renewable fuel, the primary end product will be ethanol. Increasing ethanol production and consumption will increase ethanol emissions, thus increasing aldehyde, peroxyacetyl nitrate and tropospheric ozone concentrations. Despite this potential for ethanol to affect air quality, there have been few studies monitoring ambient ethanol concentrations in the US.

To characterize temporal and spatial variations of atmospheric ethanol concentrations in the Eastern US, we have been collaborating with the five Atmospheric Integrated Research Monitoring Network (AIRMoN) sites since February 2018 to measure ethanol concentrations in event-based rain samples. To date, samples from all sites have a simple average ethanol concentration of 437 nM with a range of below detection limit (< 19 nM) to 4160 nM (n = 116). PA15 and IL11 sites have high average concentrations, 937 and 505 nM respectively, and are located downwind of ethanol production facilities. TN00, WV99, NY67 sites are located in rural areas absent significant anthropogenic ethanol sources (e.g. dense vehicles traffic and ethanol plants) and this is reflected by lower average concentrations, 321, 361, 340 nM respectively. This project is ongoing and ethanol concentrations will be investigated for correlation with a variety of  rainwater components (e.g. Mg²⁺, Ca²⁺, K⁺, Na⁺, NH₄⁺, NO₃^-, Cl^-, SO₄^2-, PO₄^3-, pH) that will be used to infer similar source and transport. In addition, air mass back trajectories will be created using the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) for each individual rain event in order to investigate emission source regions.

As the US prepares to significantly increase renewable fuel production in the next four years, this project will provide a current atmospheric ethanol concentration baseline, which is vital when determining how future emissions are affecting atmospheric composition. The wet deposition data will be combined with our previous US concentration data to create a more robust inventory to model US ethanol wet deposition flux. The ultimate goal of this research is to provide air quality modelers, climate scientists and policy-makers with empirical data of how increasing ethanol fuel consumption will affect ethanol concentrations in the atmosphere.