Chemical Speciation of PM_2.5 and PM₁₀ in South Phoenix, AZ

ABSTRACT

Phoenix, AZ, experiences high particulate matter (PM) episodes, especially in the wintertime. The spatial variation of the PM concentrations and resulting differences in exposure is of particular concern. In this study, PM_2.5 (PM with aerodynamic diameter <2.5 μm) and PM₁₀ (PM with aerodynamic diameter <10 μm) samples were collected simultaneously from the east and west sides of South Phoenix and at a control site in Tempe and analyzed for trace elements and bulk elemental and organic carbon. Measurements showed that although PM_2.5 concentrations had similar trends in temporal scale across all sites, concentrations of PM₁₀ did not. The difference in PM₁₀ concentrations and fluctuation across the three sites suggest effects of a local soil source as evidenced by high concentrations of Al, Ca, and Fe in PM₁₀. K and anthro pogenic elements (e.g., Cu, Pb, and Zn) in PM_2.5 samples on January 1 were strikingly high, suggesting the influence of New Year's fireworks. Concentrations of toxic elements (e.g., Pb) in the study presented here are not different from similar studies in other U.S. cities. Application of principal component analysis indicated two broad categories of emission sources—soil and combustion—together accounting for 80 and 90% of variance, respectively, in PM_2.5 and PM₁₀. The soil and combustion components explained approximately 60 and 30% of the variance in PM₁₀, respectively, whereas combustion sources dominated PM_2.5 (>50% variance). Many elements associated with anthropogenic sources were highly enriched, with enrichment factors in PM_2.5 an order of magnitude higher than in PM₁₀ relative to surface soil composition in the study area.

IMPLICATIONS

This study investigates the variability of PM₁₀ and PM_2.5 mass concentrations and speciation between two sites in southern Phoenix, representative of a lower income part of the city, and a comparison site in nearby Tempe, with a higher income lower minority population. The results indicate similar temporal trends in PM_2.5 concentrations and sources, although lower overall concentrations in Tempe. For PM₁₀, the highest concentrations and a unique temporal variability at one South Phoenix site suggest a particular influence of local dust sources.

ACKNOWLEDGMENTS

The authors thank the Arizona Department of Environmental Quality (ADEQ) for the funding of the project and collecting samples. The statements and conclusions in this paper are those of the contractor and not necessarily those of ADEQ or its policy committee, its employees, or its members. The mention of commercial products, their source, or their use in connection with material reported herein is not to be construed as actual or implied endorsement of such products. The authors thank Panjai Prapaipong at Arizona State University for her assistance with ICP-MS analysis.