Vertical profiling in Fairbanks shows Atmospheric River warm-air advection degrades Arctic wintertime air quality

During Arctic winter, cities like Fairbanks (interior Alaska, USA) frequently experience poor air quality because locally emitted pollutants accumulate at the surface under cold, stable conditions with low surface-level winds. While Atmospheric Rivers (ARs, corridors of warm and humid air transport) can disperse air pollution by bringing gusty winds and precipitation on land-fall, this study shows that ARs can degrade air quality in the inland Arctic. When AR warm air flows over a cold surface layer without breaking through it, the AR traps locally emitted pollutants near the ground. Shallow atmospheric profiling (<20m) in downtown Fairbanks during an AR event in December 2019 reveals sharp vertical gradients in temperature, humidity and pollutants. We observe that AR warm-air advection caused strong temperature inversions (locally 0.5-1 ̊C/m) meters above ground-level, effectively trapping surface emissions and worsening air quality. A multi-year reanalysis finds that AR-related warm air intrusions into interior Alaska are associated with historic exceedances in carbon monoxide (CO) above the legal air quality standard in Fairbanks. We show that ARs can substantially degrade wintertime air quality in inland urban Arctic environments. Tracing ARs and their influence on surface air quality may offer additional mitigation opportunities against wintertime pollution in high-latitude cities.