Differential time-lag effects of ambient PM_2.5 and PM_2.5-bound PAHs on asthma emergency department visits

Epidemiological studies have suggested the effects of ambient fine particles (PM_2.5) on asthma, but the effects of specific components of PM_2.5 on asthma remain to be explored. Here, we studied the effect of PM_2.5-bound polycyclic aromatic hydrocarbons (PAHs) on asthma acute exacerbation. The data on daily counts of emergency room visits (ERVs) were obtained from Wan Fang Medical Center, Taipei, Taiwan, from 2012 to 2015. The daily concentrations of PM_2.5 and pollutant gases were obtained from a local air quality monitoring station. The levels of PM_2.5-bound PAH were estimated by an established grid-scale model. Relative risks for ERVs as the increase in the level of ambient pollutants were calculated by using a generalized additive model of Poisson regression. In the present study, we observed statistically significant positive associations between PM_2.5 and asthma ERVs for all age groups. PM_2.5-bound PAH was also associated with asthma ERVs for all age groups. In the adult subgroup analysis, there was a significant association between PM_2.5-bound PAH and asthma ERVs at lags 1 and 2 (RR 1.289, 95% CI 1.050–1.582 and RR 1.242, 95% CI 1.039–1.485). The impacts of air pollution on the risk of pediatric asthma ERV were found to be significant for PM_2.5 at lag day 0 (RR 1.310, 95% CI 1.069–1.606). Moreover, pediatric asthma ERVs were significantly associated with the levels of PM_2.5-bound PAH at lag 1 and 2 days (RR 1.576, 95% CI 1.371–1.810 and RR 1.426, 95% CI 1.265–1.607). The study provides evidence that PM_2.5-bound PAHs were associated with an increased risk of asthma attacks. Our data further suggested that traffic exhaust is a primary source of PM_2.5-bound PAHs.