Abstract
<title>Abstract</title> <p> Background: An estimated 262 million people live with asthma worldwide. Air pollutants such as PM <sub>2.5</sub> and NO <sub>2</sub> have been linked with poor asthma control. High pollen counts and weather events, such as cold spells and heat waves, have also been linked to adverse asthma outcomes. However, the combined effect of environmental variables in relation to seasonal variations have not been well established. We conducted this study to evaluate how seasonal variation influences the relationship between daily asthma-related emergency department (ED) visits, PM <sub>2.5</sub> , NO <sub>2</sub> , pollen counts and ambient temperature in New York City (NYC). Methods: This was a retrospective time-series analysis of publicly available data between January 1st, 2023, and December 31st, 2024, conducted in five NYC boroughs (Bronx, Brooklyn, Manhattan, Queens, and Staten Island). Results: A total of 124,719 asthma-related ED visits occurred during the study period, with complete data available for 721 of 731 days (98.6%). Age ranges include 0–4 years, 5–17 years, 18–64 years and 65 + years. Gender data were not available in the NYC EpiQuery database. In the overall analysis, PM <sub>2.5</sub> was associated with increased asthma-related ED visits, with a 1.38% increase per IQR increase (95% CI: 0.97%–1.78%). Higher ambient temperature was inversely associated with ED utilization (− 5.83% per IQR increase; 95% CI: −9.48% to − 2.02%). Analyses were stratified by seasons and demonstrated significant heterogeneity. Higher PM <sub>2.5</sub> was associated with asthma-related ED visits during summer, whereas higher NO₂ was associated with ED visits during winter. Temperature showed inverse association with asthma-related ED visits during spring. Pollen levels demonstrated variable and generally inconsistent associations across seasons. Conclusion: The study shows that the environmental triggers of asthma exacerbations vary significantly in an urban setting. The contrasting effect of PM <sub>2.5</sub> , NO <sub>2</sub> , and ambient temperature along with an inconsistent association of pollen counts with asthma exacerbations highlight the need for seasonally adjusted strategies to mitigate asthma-related morbidity. </p>