Air pollution and daily mortality in the Coachella Valley, California: a study of PM10 dominated by coarse particles.

Many epidemiological studies provide evidence of an association between airborne particles, measured as PM10 (particulate matter less than 10 microm in diameter), and daily morbidity and mortality. Most of these studies have been conducted in urban areas where PM10 consists primarily of fine particles (<2.5 microm in diameter). Few studies have investigated impacts associated with coarse mode particles (>2.5 microm in diameter). We investigated associations between PM10 and daily mortality in the Coachella Valley, a desert resort and retirement area east of Los Angeles, where coarse particles of geologic origin typically comprise approximately 50-60% of PM10 and can exceed 90% during wind events. Our analysis utilized daily data on mortality from 1989 through 1992 as well as several pollutant and meteorological variables, including PM10, nitrates, sulfates, ozone, nitrogen dioxide, carbon monoxide, temperature, and relative humidity. Outcome variables included several measures of daily mortality, including all-cause, cardiovascular and respiratory mortality, and counts of deaths for those above age 50. Multivariate Poisson regression models were used to explain these health endpoints, controlling for temperature, humidity, day of the week, season, and time, using locally weighted smoothing techniques. The analysis indicated statistically significant associations between PM10 (2- or 3-day lags) and each measure of mortality. The results were robust to various model specifications, correction for autocorrelation and overdispersion, and analysis of influential observations. A 10 microg/m3 change in daily PM10 was associated with an approximately 1% increase in mortality, which is of similar magnitude to particle-associated impacts identified in urban areas. Thus, our findings provide evidence for a mortality effect of PM10 in an area where the particulate mass is dominated by coarse particles.