Acute effects of ambient air pollution on asthma emergency department visits in 10 US states

Abstract

Background: Ambient air pollution is a major risk factor for increased asthma morbidity. However, previous short-term health effect studies in the US have been limited to a small number of cities or pollutants. Objectives: This study examined acute age-specific effects of exposure to particulate matter (PM2.5, PM10), major PM2.5 components (elemental carbon [EC], organic carbon [OC], nitrate, sulfate), and gaseous pollutants (O3, NOx/NO2, SO2, CO) on emergency department (ED) visits for asthma during 2005-2014 in 10 US states (Arizona, California, Georgia, Maryland, Missouri, Nevada, New Jersey, New York, North Carolina, and Utah). Methods: We used quasi-Poisson log-linear time-series models with unconstrained distributed lags to estimate acute (8-day) effects of air pollution exposure on asthma ED visits at agency monitoring sites, controlling for meteorology, time, and influenza ED visits. We used a Bayesian hierarchical model to combine site-specific associations. We also conducted age-stratified analyses (aged 1-4, 5-17, 18-49, 50-64, and 65+). Results: We observed positive associations between 8-day exposure to particulate matter (e.g., PM2.5: rate ratio [RR] = 1.016, 95% confidence internal [CI] = [1.008, 1.025] per 6.21 μg/m³ increase), major PM2.5 components (e.g., EC: RR of 1.010 [1.002, 1.018] per 0.52 μg/m³), and gaseous pollutants (e.g., O3: RR of 1.048 [1.026, 1.070] per 0.02 ppm). Associations of traffic-related pollutants (NOx, CO, EC, and OC) were generally weaker for same day (lag 0) exposures than for exposures at longer lags before the ED visit; in contrast, PM and O3 showed strongest effects at lag day 0. Total and carbonaceous PM had more pronounced associations within younger age groups (aged 17 and below) than older age groups. Conclusions: This study reports associations between short-term air pollution exposure and increased risks of asthma ED visits. We found that short-term particular matter exposure posed a higher risk on children and adolescents than on adults.