Composition and Dynamics of the Planetary Boundary Layer in Cold and Dark Atmospheres: Meteorological Overview from the ALPACA-2022 Field Experiment

In the polar regions, the extreme cold and dark atmosphere of the winter season imposes stringent conditions on the planetary boundary-layer (PBL) leading to limited vertical atmospheric mixing and increasing the severity of air pollution episodes. Understanding the physical and chemical transformations affecting air pollution critically depends on our ability to accurately describe the dynamics of the PBL. This requires an adequate combination of modeling, ground-based observations, and vertical profile measurement systems to assess emission dispersion and transport in stratified environments. We present an overview of the meteorological conditions and PBL observations collected during the Alaskan Layered Pollution And Chemical Analysis (ALPACA) field experiment in Fairbanks, Alaska in winter 2022. Surface and vertical profile observations of radiation, turbulence, dynamics, and atmospheric composition were collected to account for surface and elevated emissions. The study area is the Tanana Valley in the Interior of Alaska, which experiences persistent synoptic anticyclonic conditions resulting in stagnant flow and limited ventilation, exacerbating air pollution levels. These conditions are interspersed with periodic transits of cyclonic air masses influencing the PBL through radiative forcing that erodes low-level temperature inversion layers and mixes local air masses into the free troposphere. This paper highlights the research objectives, experimental findings, and first results linking meteorological conditions with the observed structure and composition of the PBL under the challenging experimental conditions of the Alaskan winters. It also highlights the need for integrated surface and profiling observations of PBL dynamics and composition, which are critical for advancing across-scale modeling and enhancing predictive capabilities for air-pollution episodes locally and throughout the Arctic air shed.