Associations Between Short-term Exposure to Ambient Air Pollution and Daily Asthma-related Adult Hospital Admissions in Urumqi City, China: a Time Series Study

Abstract

Accumulating epidemiological studies have suggested that short-term exposure to ambient air pollution heightens the risk of adult asthma attacks and results in increased daily asthma-related adult hospital admissions (DARAHAs). However, epidemiological evidence from Central Asia is limited. This study aims to evaluate the short-term impact of ambient air pollution on DARAHAs in Urumqi, a city in Central Asia. The distributed lag nonlinear model (DLNM) with quasi-Poisson regression was applied to model the associations between DARAHAs and concentrations of each ambient air pollutant, including nitrogen dioxide (NO₂), fine particulate matter (PM_2.5), particulate matter with aerodynamic diameters less than 10 μm (PM₁₀), sulfur dioxide (SO₂), ozone (O₃), and carbon monoxide (CO). And the weighted quantile sum (WQS) regression was used to explore the joint associations between the mixture of air pollutants and DARAHSs and to evaluate their relative importance. Further subgroup analyses by gender and age were performed. There were a total of 9,188 asthma admissions in the study period. We found significant positive associations between DARAHAs and concentrations of NO₂, PM_2.5, SO₂, CO in single-pollutant models. In the WQS models, short-term exposure to mixed air pollutants was positively associated with DARAHAs in the overall population, as well as in the female and elderly subgroups. Specifically, based on the degree of contribution to the WQS index, CO and SO₂ had greater weights (over 40%) in both the overall population and the elderly subgroup. CO contributed more significantly to this joint effect, with a value of 51.3% in the female subgroup. In summary, our results indicated significant positive associations between both single and mixed ambient air pollutants and an increased risk of adult asthma attacks, including PM₂.₅, CO, SO₂, and NO₂. Among these pollutants, CO and SO₂ exhibited the most substantial adverse effects on asthma attacks. Subgroup analyses revealed that elderly and female patients were more susceptible to asthma attacks induced by air pollution. These results underscore the importance of reducing air pollution emissions and limiting exposure for asthmatic individuals, particularly females and the elderly.