THE USE OF TIME-RESOLVED MEASUREMENTS FOR DISTINGUISHING GASOLINE EMISSIONS FROM DIESEL EMISSIONS IN SOURCE APPORTIONMENT OF FINE PARTICLES

Abstract

ISEE-378 Abstract: The objectives of this study are to examine the use of time-resolved measurements to identify PM2.5 (particulate matter smaller than 2.5 micrometer in aerodynamic diameter) sources, especially traffic-related carbonaceous particle sources and estimate their contributions to the PM2.5 mass concentrations. In recent source apportionment studies on PM2.5 compositional data sets of daily integrated samples including total organic carbon and elemental carbon augmented by hourly averaged wind measurements, an expanded multilinear model separated gasoline emissions from diesel emissions based on the differences in the temporal patterns and directionality between the two sources, and enhanced separations of carbon-rich secondary sulfate aerosols. In Atlanta aerosol study, the sum of mass contributions from gasoline and diesel emissions identified by expanded model utilizing time-resolved wind data is 26% of the PM2.5 mass concentration. This total is consistent with 21% from four traffic-related sources deduced by bilinear Positive Matrix Factorization (PMF) study with eight carbon fractions. Also, the contribution of 56% from expanded model identified two secondary sulfate aerosols is consistent with the sum of two secondary sulfate aerosols identified by PMF (56%) with eight carbon fractions. However, the gasoline emissions identified by ME tend to have more contribution (15%) than identified by PMF with eight carbon fractions (6%). The diesel emissions contributed 11% in expanded model study and 15% in PMF study. In this study, the expanded model studies utilizing time-resolved data are compared with PMF studies utilizing temperature-resolved carbon fractions to elucidate the usefulness of time-resolved measurements. Since the EPA Speciation Trends Network (STN) does not provide temperature-resolved carbon fractions that have been shown to aid separating gasoline and diesel emissions in source apportionment studies, the expanded model that utilizes time-resolved wind measurements along with the particle speciation data can be used to separate these two source types providing epidemiological studies source-specific exposure to the traffic emissions.