Personal and ambient air pollution exposures and lung function decrements in children with asthma

Abstract

Background: Epidemiologic studies have shown associations between asthma outcomes and outdoor air pollutants such as nitrogen dioxide and particulate matter mass < 2.5 μm in diameter (PM2.5). Independent effects of specific pollutants have been difficult to detect because most studies have relied on highly correlated central-site measurements. Objectives: This study was designed to evaluate the relationship of daily changes in percent-predicted forced expiratory volume in 1 sec (FEV1) with personal and ambient air pollutant exposures. Methods: For 10 days each, we followed 53 subjects with asthma who were 9-18 years of age and living in the Los Angeles, California, air basin. Subjects self-administered home spirometry in the morning, afternoon, and evening. We measured personal hourly PM2.5 mass, 24-hr PM2.5 elemental and organic carbon (EC-OC), and 24-hr NO2, and the same 24-hr average outdoor central-site (ambient) exposures. We analyzed data with transitional mixed models controlling for personal temperature and humidity, and as-needed β2-agonist inhaler use. Results: FEV1 decrements were significantly associated with increasing hourly peak and daily average personal PM2.5 but not ambient PM2.5. Personal NO2 was also inversely associated with FEV1. Ambient NO2 was more weakly associated. We found stronger associations among 37 subjects not taking controller bronchodilators as follows: Personal EC-OC was inversely associated with morning FEV1; for an interquartile increase of 71 μm/m3 1-hr maximum personal PM2.5, overall percent-predicted FEV1 decreased by 1.32% [95% confidence interval (CI), -2.00 to -0.65%]; and for an interquartile increase of 16.8 ppb 2-day average personal NO2, overall percent-predicted FEV1 decreased by 2.45% (95% CI, -3.57 to -1,33%). Associations of both personal PM2.5 and NO2 with FEV1 remained when co-regressed, and both confounded ambieur NO2. Conclusions: Independent pollutant associations with lung function might be missed ambient data alone. Different sets of causal components are suggested by independence of FEV1 associations with personal PM2.5 mass from associations with personal NO2.