Increasing ethanol consumption as a renewable fuel: How will vehicle ethanol emissions impact the atmosphere?

U.S. 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. The U.S is now at a pivotal crossroads with respect to ethanol usage as a fuel with vehement calls to both increase and decrease its production. Much of the evidence for both sides of the debate depends on the life cycle analysis of ethanol production (e.g. water, fossil fuel and feedstock consumption, greenhouse gas emissions) but an important uncertainty not adequately addressed by either side in this debate is “What are the environmental ramifications of ethanol usage and subsequent emissions on a variety of fundamental properties of the atmosphere?” Vehicle ethanol emissions can have an impact on the oxidizing capacity of the atmosphere and acid-generating capacity of atmospheric waters as well as increase acetaldehyde, peroxyacetyl nitrate and tropospheric ozone production. Despite this, there is a lack of data available to investigate ethanol emission impacts on atmospheric chemistry due to the difficulty in measuring ambient aqueous phase ethanol concentrations. Low molecular weight saturated straight chain alcohols (C1-C4) are notoriously difficult to quantify in aqueous environmental matrices because they exist in low concentrations, are structurally similar to water, have poor molar absorptivities, and are hard to derivatize for spectroscopic analysis. To provide missing ambient ethanol concentration data to the scientific community, low concentration aqueous phase analysis techniques were developed and novel measurements of ethanol in atmospheric waters (e.g. rainwater, condensates, ice core) and surface waters (e.g. lakes, estuaries, oceans) are reported. A method to measure the carbon isotopic composition of ethanol at natural abundance levels was also developed and preliminary isotope signatures of ethanol emission sources are reported. The ethanol concentration data obtained will be used to estimate the ethanol global wet deposition sink and predict whether varying surface waters act as a source or sink of ethanol. Isotopic source signature data will be used to estimate the percent contribution of vehicle emissions to the atmospheric ethanol budget. The goal is to provide air quality modelers, climate scientists and policy-makers with empirical data for ethanol source/sink inventories in hopes of providing knowledge of how increasing ethanol fuel consumption will impact atmospheric chemistry and the carbon cycle. With the U.S. renewable fuel standard requiring an increase from the present production of 15 billion gallons to 36 billion gallons of renewable fuel by 2022, it is essential that the entities involved in deciding the fate of U.S. fuel consumption have knowledge of all the advantages and disadvantages of increased ethanol consumption, including the atmospheric impacts of direct ethanol emissions.