Characterization of Biofuels Blends: Emissions, Permeation and Apportionment of Volatile Organic Compounds.

Abstract

The formulation of motor vehicle fuels can alter the magnitude and composition of evaporative and exhaust emissions that are associated with environmental and health impacts. The goal of this research was to investigate consequences of using the new vehicle fuels, including bioethanol and biodiesel blends. Laboratory studies were used to characterize the composition of liquid and vapors of gasoline-ethanol and diesel-biodiesel blends; assess the collinearity of fuel profiles used in receptor modeling; evaluate permeation rates and permeant compositions through personal protective equipment (PPE) materials; and measure exhaust emissions from diesel engines. In an ambient study conducted in Detroit, daily volatile organic compound (VOC) levels were measured near a major highway, and VOC sources were apportioned using positive matrix factorization, a receptor model. The compositions of biofuel blends and conventional fuels differed significantly. Predictions of vapor concentrations were highly correlated to measurements, but activity coefficients are needed for ethanol blends. Petroleum diesel and biodiesel blends, and their vapors had similar compositions, which were distinct from those of gasoline. In permeation tests, breakthrough time and permeation rate strongly depended on the fuel-PPE material combination, and permeants were enriched in benzene and other VOCs. Recommendations are made regarding PPE appropriate for the current fuels. Diesel engine exhaust emissions depended on engine calibration, load, fuel and aftertreatment systems. Biodiesel blends generally reduced emissions of particulate matter, nonmethane hydrocarbons and VOCs, however, nitrogen oxides and formaldehyde emissions increased in certain conditions. In the ambient study, VOC concentrations were generally low and varied with both seasonal and weekly patterns. The major sources were identified as gasoline exhaust, diesel exhaust, fuel evaporation, industrial emissions, biomass burning, and others. The study provides information regarding VOC profiles of the new fuels, their vapors, diesel exhaust, and ambient levels near a highway site. These profiles can be incorporated into receptor modeling. The permeation study provides guidance for selecting PPE materials. Study results can be used to assess exposure and health impacts resulting from the use of new fuels and biofuel blends.