Environmental safety thresholds for children with asthma symptoms: a prospective study of multitemporal air pollution exposure and longitudinal trajectories.

BACKGROUND

Current air quality standards are designed for healthy populations, while their adequacy in protecting children with asthma symptoms remains unclear. We prospectively delineated the effects of air pollution exposures across multiple time windows on the longitudinal trajectories of childhood asthma.

METHODS

This 18-month prospective cohort study involved 1,545 high-risk children presenting with asthma symptoms. We utilized latent class growth analysis (LCGA) to identify distinct disease phenotypes, and applied generalized estimating equations (GEE) and LASSO-logistic regression to evaluate the independent associations of individual pollutants across 1-, 3-, and 12-month exposure windows. Finally, Temporal effect decomposition and restricted cubic spline (RCS) models separated long-term cumulative exposures from short-term fluctuations to explore potential safety thresholds.

RESULTS

We identified sustained remission (79.0%) and persistent high-risk (21.0%) trajectories. Multi-temporal modeling revealed that sulfur dioxide (SO2) was uniquely and consistently associated with a higher probability of high-risk trajectory assignment across all windows. Conversely, PM10 and PM2.5 were associated with protective effects, while behavioral heatmaps indicated that high particulate matter (PM) concentrations may have prompted outdoor avoidance and reduced physical activity. High long-term (12-month) SO2 exposure was associated with a baseline risk of persistent symptoms of 25.1% (compared to 10.4% in optimal conditions), whereas short-term (1-month) fluctuations corresponded to an additional 4% absolute risk. The potential safety threshold for long-term SO2 exposure was remarkably low at 8.5 μg/m3.

CONCLUSION

The reference level for long-term SO2 exposure among high-risk children is substantially lower than current conventional standards. Ambient SO2 serves as a critical environmental warning indicator to guide early, individualized preventive interventions in pediatric clinical practice.