Air quality impacts of achieving U.S. renewable fuel mandates

The current US Renewable Fuel Standard (RFS2) requires increasing amounts of biofuel production through 2022. In this analysis we use lifecycle assessment, air dispersion modeling, and health risk assessment to estimate air pollution and related health impacts of the production and use of an additional 7.5 billion gallons of corn grain ethanol and 5 billion gallons of corn stover cellulosic ethanol. Specifically, we considered three potential increases in ethanol volumes associated with moving from the Renewable Fuel Standard - Phase 1 (RFS1) to Phase 2 (RFS2): (i) a 5 billion gallon increase in cellulosic (corn stover-derived) ethanol, (ii) a 7.5 billion gallon increase in corn-derived ethanol, and (iii) a combination of the two (5 billion gallons of cellulosic ethanol plus 7.5 billion gallons of corn ethanol). We use the Greenhouse Gases, Regulated Emissions and Energy Use in Transportation Model (GREET) to estimate the life cycle emissions associated with the production and use of both the ethanol fuels and an energy equivalent amount of gasoline. Temporal and spatial information was also utilized in order to allocate the lifecycle emissions as necessary for photochemical modeling. The Sparse Matrix Operator Kernel Emissions (SMOKE) model was used to calculate the base case emissions. We use the CAMx reactive photochemical air quality model to estimate the resulting changes in ozone and PM _2.5 concentrations, relative to a non-RFS scenario (i.e., relative to consuming an energy-equivalent amount of gasoline), for the entire United States using 2005 as a base year. Finally, we use BenMAP to evaluate the potential health impacts from the anticipated air quality changes. Preliminary results for February and August indicate that population-weighted ambient PM _2.5 concentration increases are up to 189% higher for RFS than for the non-RFS scenario; analogous values for nitrate PM _2.5 are 15%-150% higher for RFS. Concentration impacts vary in space and time; predicted concentrations exhibit greater spatial variability for RFS than for the non-RFS scenario. Preliminary findings from the PM _2.5 health risk assessment suggest greater impacts from RFS2 scenarios than from an energy equivalent amount of gasoline.