Aged and Obscured\nWildfire Smoke Associated with Downwind\nHealth Risks

Fine-mode particulate matter (PM<sub>2.5</sub>) is a\nhighly detrimental\nair pollutant, regulated without regard for chemical composition and\na chief component of wildfire smoke. As wildfire activity increases\nwith climate change, its growing continental influence necessitates\nmultidisciplinary research to examine smoke’s evolving chemical\ncomposition far downwind and connect chemical composition-based source\napportionment to potential health effects. Leveraging advanced real-time\nspeciated PM<sub>2.5</sub> measurements, including an aerosol chemical\nspeciation monitor in conjunction with source apportionment and health\nrisk assessments, we quantified the stark pollution enhancements during\npeak Canadian wildfire smoke transport to New York City over June\n6–9, 2023. Interestingly, we also observed lower-intensity,\nbut frequent, multiday wildfire smoke episodes during May–June\n2023, which risk exposure misclassification as generic aged organic\nPM<sub>2.5</sub> via aerosol mass spectrometry given its extensive\nchemical transformations during 1 to 6+ days of transport. Total smoke-related\norganic PM<sub>2.5</sub> showed significant associations with asthma\nexacerbations, and estimates of in-lung oxidative stress were enhanced\nwith chemical aging, collectively demonstrating elevated health risks\nwith increasingly frequent smoke episodes. These results show that\navoiding underestimated aged biomass burning PM<sub>2.5</sub> contributions,\nespecially outside of peak episodes, necessitates real-time chemically\nresolved PM<sub>2.5</sub> monitoring to enable next-generation health\nstudies, models, and policy under far-reaching wildfire impacts in\nthe 21st century.