Composition and Dynamics of the Planetary Boundary Layer in Cold and Dark Atmospheres: Meteorological Overview from the ALPACA-2022 Field Experiment
Journal Article
Overview
abstract
Abstract; 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.; ; Significance Statement; This article provides an overview of the meteorology during the Alaskan Layered Pollution and Chemical Analysis (ALPACA)-2022 winter field experiment. It also presents observations designed to better understand the physical processes influencing the planetary boundary layer (PBL) and their role in wintertime Arctic air pollution. It describes the synoptic meteorological conditions throughout the experiment and the diverse instrumental platforms used to study the dynamics and composition of the Arctic polluted PBL for the first time. The article emphasizes the importance of multi-instrumental platforms to improve understanding of the PBL composition and dynamics in the context of Arctic air pollution. This is particularly relevant in conditions with limited photochemistry and in areas experiencing very cold, stable environments that exacerbate pollution levels. The observations are used to improve meteorological and air quality model simulations.;
