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.

Intra-urban spatial variability of PM2.5-bound carbonaceous components

“…2(a–f) shows correlation coefficients and CODs for concentrations of organic molecular markers, EC, and OC measured at the four sites from March 2008eMarch 2009. OC concentrations had higher correlation across sites ( r = 0.80–0.85) and lower CODs (0.17–0.20) than EC, consistent with the observations of other studies (Krudysz et al, 2009; Cheung et al, 2011), which is likely caused by the smaller number of EC source types and different source strength across different sampling sites. Heavier odd n -alkanes (C 27 , C 29 , C 31 , C 33 ) are primarily of biogenic origin (Simoneit and Mazurek, 1982; Rogge et al, 1993b; Cass, 1998).…”

“…The total average concentrations of n -alkanes, PAHs and steranes in Denver were higher than those observed in Long Beach, CA (Krudysz et al, 2009). The average concentrations of these organic molecular markers were less varied across different sites in Denver than in Vancouver, BC (Cheng et al, 2004, 2006), Atlanta, GA (Li et al, 2009) and Hong Kong, China (Guo et al, 2003; Ho et al, 2003).…”

“…Lower S/N ratios for some species (e.g., tridecanoic acid and heptadecanoic acid) suggest higher analytical uncertainty, and correspond to a larger number of observations below detection limits. The CV value is a robust metric used to assess the temporal variation of species concentrations (Dutton et al, 2009b; Krudysz et al, 2009). At all four sampling sites, the CVs of most organic molecular markers were close to or higher than unity.…”

“… a This study. b Krudysz et al (2008). c Krudysz et al (2009). d Cheng et al (2004). e Cheng et al (2006). f Li et al (2009). g Ho et al (2003). h Guo et al (2003). …”

Intra-urban spatial variability and uncertainty assessment of PM2.5 sources based on carbonaceous species

“…Steranes are reliable organic markers for motor oil combustion (Kleeman et al, 2008), while EC is often but not exclusively associated with diesel vehicle emissions (Schauer, 2003; Diaz-Robles et al, 2008; Krudysz et al, 2009). This association is supported by observation that EC concentrations show a greater proportional reduction on the weekend than that in overall traffic counts (Dutton et al, 2010a).…”