Wintertime vertical distribution of air pollution in suburban Fairbanks during the ALPACA 2022 field campaign

The Alaskan Layered Pollution and Chemical Analysis (ALPACA) field campaign investigated the sources and processing of wintertime urban pollution in Fairbanks, Alaska in January and February 2022. Several sites located around the city of Fairbanks collected data to study the underexplored cold and dark wintertime dynamical, physical and chemical processes driving air pollution, both outdoors and indoors. We deployed a tethered balloon system at a farm field site near the University of Alaska (UAF) to specifically investigate the vertical layering of pollution and influence of different emission altitudes on surface pollution levels. The study site is located in a suburban area, west of downtown Fairbanks. Observational efforts there focused mainly on surface exchanges and the vertical distribution of pollutants in relation to the boundary layer structure, specifically under stable (inversion) conditions. Instruments at the UAF-farm provided continuous ground measurements of aerosol physical, optical and chemical properties, trace gases (O3, CO, N2O) and meteorology. The newly designed Modular Multiplatform Air Compatible Measurement System (MoMuCAMS) was deployed with a tethered-balloon (helikite) to sample air up to 350 m above ground level, providing information on the vertical distribution and mixing processes of atmospheric pollutants. Instruments onboard MoMuCAMS provided information on aerosol characteristics (particle number concentration, size distribution, absorption coefficient and chemical composition), trace gases (CO2, O3, CO, N2O, NOx), and meteorology. MoMuCAMS performed 21 flights between January 26 and February 25, 2021, collecting roughly 140 individual profiles of varying altitude under different boundary layer conditions, intercepting pollution plumes at different heights and of different composition. Given the suburban location of the study site, we measured the influence of polluted air from the city and “cleaner” air from more remote origins. We will show how the vertical structure of the atmosphere and the frequently occurring temperature inversions affect transport and dispersion of pollution at different heights and how different meteorological conditions affect local air circulation and pollution at the study site.