Ambient air pollutant concentrations and asthma-related hospital admissions during COVID-19 transport restrictions

Exposure to air pollution is a known risk factor for asthma exacerbations and hospitalisations. This study aimed to identify if COVID-19 transport restrictions led to improvements in air quality in Dublin and if this had an impact on asthma-related hospital admissions.

This was a population-based retrospective cohort study.

Daily concentration levels of particulate matter (PM_2.5 and PM₁₀) and nitrogen dioxide (NO₂) were obtained from the Environmental Protection Agency (EPA). The Hospital In-Patient Enquiry (HIPE) system provided the daily number of asthma-related hospital admissions in Dublin. The figures for 2018-2019 were compared with the period of transport restrictions (from March 2020).

During the period of transport restrictions, there was a significant decrease in mean daily concentrations in both PM_2.5 (8.9 vs 7.8 μg/m³, P = 0.002) and NO₂ (24.0 vs 16.7 μg/m³, P < 0.001). There was also a significant reduction in the mean number of daily asthma admissions (4.5 vs 2.8 admissions, P < 0.001). Only NO₂ showed a statistically significant correlation with asthma admissions (r = 0.132, P < 0.001).

Transport restrictions introduced to mitigate against COVID-19 led to lower pollutant levels and improved air quality. Previously described associations between pollutants and asthma would indicate that these improvements in air quality contributed to the reduction in asthma-related admissions. The complex nature of PM is the likely explanation for the lack of correlation between its concentration and asthma admissions, unlike NO₂ whose primary source is vehicular emissions. Public Health needs to advocate for transport policies, which can improve air quality and hence improve human health.