Intra-community spatial variation of size-fractionated organic compounds in Long Beach, California

Abstract

Quantification of the size distributions of organic molecular markers can provide information about the origin of the carbonaceous particulate matter (PM). Organic molecular marker spatial variability studies provide data that are vital to an accurate determination of a population's exposure to PM from various sources. We have investigated the intra-community spatial variation of size-segregated PM [0–0.25 μm (ultrafine), 0.25-2.5 μm (accumulation), and 2.5-10 μm (coarse)) ] in a southern California community. The highest concentrations of individual organic compounds were found in the ultrafine fraction, followed by the accumulation and coarse size fractions. Correlations between the three size fractions were weak between compounds in the coarse and corresponding ultrafine and accumulation particles, implying that the coarse PM organic compounds were emitted by different sources than those that emit ultrafine and accumulation mode PM. Evidence of the incomplete combustion of gasoline was found in the ultrafine and accumulation size fractions, while possible diesel emissions were traced to ultrafine particles. Coefficients of divergence and coefficients of variation were investigated to determine the spatial and temporal variability of individual organic compounds. Spatial divergence in organic compounds was comparatively high, but it did not differ appreciably between size fractions or between compound classes. Elemental carbon and tracer compounds, which originate from a few sources, showed higher spatial divergence than organic carbon whose numerous sources can be local and regional. Spatial and temporal variability were not different from each other for this data set and, therefore, it is not possible to determine whether variability in concentrations between sampling sites or the length of the sampling campaign is more important for health effects studies.