Aged and obscured wildfire smoke associated with downwind health risks

Fine-mode particulate matter (PM2.5) is a highly detrimental air pollutant produced in large quantities from wildfires, which are increasing with climate change. Leveraging advanced chemical measurements in conjunction with source apportionment and health risk assessments, we quantified the stark pollution enhancements during Canadian wildfire smoke transport to New York City at its peak over June 6-9, 2023. Interestingly, we also observed lower-intensity, but frequent, multi-day wildfire smoke episodes during May-June 2023, which risk exposure misclassification as generic aged organic PM2.5 given its extensive chemical transformations during 1-6+ days of transport. This smoke-related organic PM2.5 showed significant associations with asthma exacerbations, and estimates of in-lung oxidative stress demonstrate the health risks of increasingly-frequent smoke episodes and potential enhancements with chemical aging. Avoiding underestimated contributions of aged biomass burning PM2.5, especially outside of peak pollution episodes, necessitates real-time chemically-resolved monitoring to enable next-generation health studies, models, and policy under far-reaching wildfire impacts.