Tracking Variations in Heatwave-Induced Aerosol Concentration and Chemical Composition Following Emission Reductions in NYC’s Downwind Region

While emission reductions from energy market shifts and regulatory controls have lowered primary fine particulate matter (PM2.5) concentrations over the past decade, heatwaves can amplify PM2.5 and potentially reverse these gains, a phenomenon not fully tracked. This study examines the heatwave-induced aerosol variations using aerosol chemical component measurements (2011, 2018, and 2023) and routine PM2.5 mass concentrations in New York City’s downwind region. Results indicate that, under current emission reductions, heatwave PM2.5 concentrations decreased by 41% (daytime), 30% (nighttime), and 26% (rush hour), significantly greater than nonheatwave reductions (∼20%), highlighting enhanced PM2.5 mitigation effects during heatwaves. Particle sulfate, ammonium, and locally formed secondary organic aerosol (SOA) were the dominant contributors to heatwave aerosol reductions, closely tracking precursor emission changes. Additionally, sulfate and local SOA showed similar reduction rates (∼0.2 μg m–3 per year), while regional SOA remained independent of volatile organic compound (VOC) emission reductions, suggesting a more complex formation process. Further reductions in local SOA concentrations are expected with ongoing emission controls, although continuous monitoring remains crucial. These findings will also offer valuable insights and serve as a reference for similar research in other regions.