Cardiovascular Mortality in Phoenix: PM1 Is a Better Indicator Than PM2.5.
EPA has obtained a 3-year database of particulate matter (PM) in Phoenix, AZ from 1995 - 1997 that includes elemental analysis by XRF of daily PM2.5. During this time period PM1 and PM2.5 TEOMs were run simultaneously for about 7 months during two periods of the year. Regression of the inter-modal PM (PM2.5 - PM1) from the TEOM monitors against the soil component of PM2.5, reconstructed form the XRF elemental composition, resulted in an estimated coefficient of 1.3 times soil for inter-modal PM (Kegler et al., 2000). This relationship was used with the reconstructed soil from the 3-year time-series of filter PM2.5 to estimate a 3-year time-series of PM1. The estimated PM1 concentration was then used as a surrogate for personal exposure to ambient PM1 in an epidemiologic analysis using a model previously developed at the University of Washington. In the earlier analysis (Mar et al., 2000), relative risks were not statistically significant for filter measurements of PM2.5; the relative risk for PM - (the soil component of PM2.5) was significant only for lag 1. However, in this study, the PM1 estimated by PM2.5 - (1.3 times the soil component of PM2.5) was significant for lags 1, 3, and 5 days. The coefficient estimate of 1.3 suggests that some PM material other than soil is present in the inter-modal mass. The inter-modal mass, when used as an exposure surrogate, did not yield a statistically significant risk for any lag. These results indicate the need to measure PM1 both in monitoring studies undertaken to provide data for epidemiologic analyses and in exposure modeling studies. It also points out the need to determine the chemical nature of inter-modal PM.