Arctic transport of North American and Canadian wildfire aerosols

Wildfires are becoming increasingly frequent and intense under ongoing climate change, with the potential to emit and transport particles, from black carbon to nutrient-bearing aerosols, into remote and fragile ecosystems such as the Arctic. Yet, direct observations of long-range wildfire aerosol transport into the Arctic remain scarce, limiting our understanding of its impacts on the wider ecosystem and human health. Here, we present shipborne particulate matter (PM) measurements documenting the spatial extent and characteristics of PM in the Arctic during the 2023 North American and Canadian wildfires. Semi-continuous monitoring aboard an icebreaker from 12th September to 11th October 2023, spanning 11,000 km from Iceland to Alaska via the Northwest Passage, measured PM size fractions (PM0.3, PM0.5, PM1.0, PM2.5, PM5 and PM10) at 1-min intervals. This identified four high PM events along the cruise track, with the most intense event occurring on 28th September, when visible wildfire smoke was observed north of Victoria Island, coinciding with a peak PM2.5 count of 58 × 106 counts m−3. This smoke event was not detected by the National Oceanic and Atmospheric Administration Hazard Mapping System Fire and Smoke Product, highlighting limitations of satellite-derived smoke monitoring in remote regions. Daily mean PM2.5 concentrations were also compared to the WHO 24-hr guidelines, where they spiked at or above the 15 μg m−3 24-hr guideline during the latter part of the cruise. These findings demonstrate the potentially extensive reach of North American and Canadian wildfire aerosols into the Arctic, with implications for remote community health and the adequacy of current smoke monitoring frameworks.