Coarse Particulate Air Pollution and Respiratory Emergency Room Visits in California

Though respiratory disease has been strongly connected to fine particulate air pollution (particles less than 2.5 microns in diameter), evidence has been mixed regarding the effects of coarse particles (particles between 2.5 and 10 microns) on respiratory health. In this study, we used air monitoring data and emergency room visit data for 2005-2008 to evaluate the relationship between coarse particle levels and respiratory emergency room visits in 35 California counties. We utilized a time-stratified case-crossover design to control for seasonal influences and time-invariant confounders, and limited the study population to those residing within 20km of available coarse particle monitoring to improve exposure assessment. Controlling for daily temperature and day of week, we found significant associations between respiratory admissions and coarse particle levels 1 and 2 days prior. More specifically, asthma visits demonstrated similar but stronger associations (excess risk per 10 micrograms/m^3 = 3.3%; 95% CI: 2.0, 4.6 for 2-day lag) that were robust to further adjustment by other air pollutants. No significant associations were observed for visits for chronic obstructive pulmonary disease, pneumonia, or acute respiratory infections. Coarse particle exposure may lead to asthma exacerbation, and efforts should be made to reduce exposures in asthmatics.