Air conditioning and source-specific particles as modifiers of the effect of PM10 on hospital admissions for heart and lung disease

Studies on acute effects of particulate matter (PM) air pollution show significant variability in exposure-effect relations among cities. Recent studies have shown an influence of ventilation on personal/indoor-outdoor relations and stronger associations of adverse effects with combustion-related particles. We evaluated whether differences in prevalence of air conditioning (AC) and/or the contribution of different sources to total PM10 emissions could partly explain the observed variability in exposure-effect relations. We used regression coefficients of the relation between PM10 and hospital admissions for chronic obstructive pulmonary disease (COPD), cardiovascular disease (CVD), and pneumonia from a recent study in 14 U.S. cities. We obtained data on the prevalence of AC from the 1993 American Housing Survey and data on PM10 emissions by source category, vehicle miles traveled (VMT), and population density from the U.S. EPA. We analyzed data using meta-regression techniques. PM10 regression coefficients for CVD and COPD decreased significantly with increasing percentage of homes with central AC when cities were stratified by whether their PM10 concentrations peaked in winter or nonwinter months. PM10 coefficients for CVD increased significantly with increasing percentage of PM10 emission from highway vehicles, highway diesels, oil combustion, metal processing, decreasing percentage of PM10 emission from fugitive dust, and increasing population density and VMT/mile(2). In multivariate analysis, only percentage of PM10 from highway vehicles/diesels and oil combustion remained significant. For COPD and pneumonia, associations were less significant but the patterns of the assocations were similar to that for CVD. The results suggest that air conditioning and proportion of especially, traffic-related particles significantly modify the effect of PM10 on hospital admissions, especially for CVD.