Is local air pollution concentration a moderator or mediator of the association between residential greenspace and pediatric asthma exacerbations? A longitudinal study of pediatric patients in Philadelphia, Pennsylvania
| Authors: | Yun-Ting Yen, Leah H. Schinasi, Brisa N. Sánchez, Steven Melly, Kari Moore, Christopher B. Forrest, Chén C. Kenyon, Michelle Kondo, Anneclaire J. De Roos |
| Year: | 2025 |
| Type: | Scientific Journal |
| Station: | Northern Research Station |
| DOI: | https://doi.org/10.1016/j.ijheh.2025.114546 |
| Source: | International Journal of Hygiene and Environmental Health |
Abstract
Background: Despite mixed evidence supporting the link between greenspace and asthma exacerbations, several studies suggest a negative association. The mechanisms underlying this relationship are unclear, with air pollution concentrations potentially playing a key role. This study investigated whether air pollution concentrations modify or mediate the relationship between residential greenspace and pediatric asthma exacerbations.
Methods: Data were drawn from a pediatric asthma cohort at Children's Hospital of Philadelphia (2011–2016), including children aged <18 years. Participants were followed from their initial visit until their first asthma exacerbation. Greenspace (tree canopy, grass/shrub cover) near homes was assessed. Daily air pollution data, including PM2.5, ozone, NO2, and SO2, were obtained from the US Environmental Protection Agency. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated, adjusting for individual and neighborhood characteristics. Effect modification by air pollution concentrations was tested, and causal mediation analyses were conducted.
Results: On days with high SO2 concentrations, children living near the highest quartile of tree canopy coverage had a 14% lower incidence of asthma exacerbations compared to those in the lowest quartile (HR = 0.86, 95% CI = 0.74, 0.98). Conversely, on days with low SO2 concentrations, tree canopy coverage was associated with a nonsignificant 12% higher incidence (HR = 1.12, 95% CI = 0.97, 1.28). Similar patterns were observed for NO2, but no interactions were found for PM2.5 or ozone. Mediation analyses indicated no significant mediation by air pollution.
Conclusion: In urban areas with high SO2 or NO2 levels, greenspace near homes may support children with asthma by mitigating air pollution's impact, suggesting greenspace-based urban strategies.