Coupled Air Quality and Boundary-Layer Meteorology in Western U.S. Basins during Winter: Design and Rationale for a Comprehensive Study

A. Gannet Hallar Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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Steven S. Brown NOAA/Chemical Sciences Laboratory, Boulder, Colorado

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Erik Crosman Department of Life, Earth, and Environmental Sciences, West Texas A&M University, Canyon, Texas

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Kelley C. Barsanti Department of Chemical and Environmental Engineering, Center for Environmental Research and Technology, University of California, Riverside, Riverside, California

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Christopher D. Cappa Department of Civil and Environmental Engineering, University of California, Davis, Davis, California

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Ian Faloona Department of Land, Air and Water Resources, University of California, Davis, Davis, California

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Jerome Fast Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington

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Heather A. Holmes Department of Chemical Engineering, University of Utah, Salt Lake City, Utah

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John Horel Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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John Lin Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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Ann Middlebrook NOAA/Chemical Sciences Laboratory, Boulder, Colorado

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Logan Mitchell Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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Jennifer Murphy Department of Chemistry, University of Toronto, Toronto, Ontario, Canada

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Caroline C. Womack Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, and NOAA/Chemical Sciences Laboratory, Boulder, Colorado

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Viney Aneja Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

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Munkhbayar Baasandorj Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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Roya Bahreini Department of Environmental Sciences, University of California, Riverside, Riverside, California

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Robert Banta NOAA/Chemical Sciences Laboratory, Boulder, Colorado

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Casey Bray Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

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Alan Brewer NOAA/Chemical Sciences Laboratory, Boulder, Colorado

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Dana Caulton Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming

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Joost de Gouw Cooperative Institute for Research in Environmental Sciences, and Department of Chemistry, University of Colorado Boulder, Boulder, Colorado

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Stephan F.J. De Wekker Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia

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Delphine K. Farmer Department of Chemistry, Colorado State University, Fort Collins, Colorado

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Cassandra J. Gaston Department of Atmospheric Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida

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Sebastian Hoch Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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Francesca Hopkins Department of Environmental Sciences, University of California, Riverside, Riverside, California

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Nakul N. Karle Environmental Science and Engineering, The University of Texas at El Paso, El Paso, Texas

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James T. Kelly Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina

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Kerry Kelly Department of Chemical Engineering, University of Utah, Salt Lake City, Utah

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Neil Lareau Atmospheric Sciences and Environmental Sciences and Health, University of Nevada, Reno, Reno, Nevada

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Keding Lu State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Science and Engineering, Peking University, Beijing, China

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Roy L. Mauldin III Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, Colorado

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Derek V. Mallia Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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Randal Martin Civil and Environmental Engineering, and Utah Water Research Laboratory, Utah State University, Logan, Utah

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Daniel L. Mendoza Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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Holly J. Oldroyd Department of Civil and Environmental Engineering, University of California, Davis, Davis, California

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Yelena Pichugina NOAA/Chemical Sciences Laboratory, Boulder, Colorado

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Kerri A. Pratt Department of Chemistry, University of Michigan, Ann Arbor, Michigan

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Pablo E. Saide Department of Atmospheric and Oceanic Sciences, and Institute of the Environment and Sustainability, University of California, Los Angeles, Los Angeles, California

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Philip J. Silva Food Animal Environmental Systems Research Unit, USDA-ARS, Bowling Green, Kentucky

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William Simpson Department of Chemistry and Biochemistry, and Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska

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Britton B. Stephens Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado

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Jochen Stutz Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California

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Amy Sullivan Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

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Abstract

Wintertime episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys worldwide. These episodes often arise following development of persistent cold-air pools (PCAPs) that limit mixing and modify chemistry. While field campaigns targeting either basin meteorology or wintertime pollution chemistry have been conducted, coupling between interconnected chemical and meteorological processes remains an insufficiently studied research area. Gaps in understanding the coupled chemical–meteorological interactions that drive high-pollution events make identification of the most effective air-basin specific emission control strategies challenging. To address this, a September 2019 workshop occurred with the goal of planning a future research campaign to investigate air quality in western U.S. basins. Approximately 120 people participated, representing 50 institutions and five countries. Workshop participants outlined the rationale and design for a comprehensive wintertime study that would couple atmospheric chemistry and boundary layer and complex-terrain meteorology within western U.S. basins. Participants concluded the study should focus on two regions with contrasting aerosol chemistry: three populated valleys within Utah (Salt Lake, Utah, and Cache Valleys) and the San Joaquin Valley in California. This paper describes the scientific rationale for a campaign that will acquire chemical and meteorological datasets using airborne platforms with extensive range, coupled to surface-based measurements focusing on sampling within the near-surface boundary layer, and transport and mixing processes within this layer, with high vertical resolution at a number of representative sites. No prior wintertime basin-focused campaign has provided the breadth of observations necessary to characterize the meteorological–chemical linkages outlined here, nor to validate complex processes within coupled atmosphere–chemistry models.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: A. Gannet Hallar, gannet.hallar@utah.edu

Abstract

Wintertime episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys worldwide. These episodes often arise following development of persistent cold-air pools (PCAPs) that limit mixing and modify chemistry. While field campaigns targeting either basin meteorology or wintertime pollution chemistry have been conducted, coupling between interconnected chemical and meteorological processes remains an insufficiently studied research area. Gaps in understanding the coupled chemical–meteorological interactions that drive high-pollution events make identification of the most effective air-basin specific emission control strategies challenging. To address this, a September 2019 workshop occurred with the goal of planning a future research campaign to investigate air quality in western U.S. basins. Approximately 120 people participated, representing 50 institutions and five countries. Workshop participants outlined the rationale and design for a comprehensive wintertime study that would couple atmospheric chemistry and boundary layer and complex-terrain meteorology within western U.S. basins. Participants concluded the study should focus on two regions with contrasting aerosol chemistry: three populated valleys within Utah (Salt Lake, Utah, and Cache Valleys) and the San Joaquin Valley in California. This paper describes the scientific rationale for a campaign that will acquire chemical and meteorological datasets using airborne platforms with extensive range, coupled to surface-based measurements focusing on sampling within the near-surface boundary layer, and transport and mixing processes within this layer, with high vertical resolution at a number of representative sites. No prior wintertime basin-focused campaign has provided the breadth of observations necessary to characterize the meteorological–chemical linkages outlined here, nor to validate complex processes within coupled atmosphere–chemistry models.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: A. Gannet Hallar, gannet.hallar@utah.edu

Winter episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys across the globe [e.g., Yamuna Basin, India (Tiwari and Kulshrestha 2019); Tokyo Basin, Japan (Osada et al. 2019); Taiyuan Basin, China (Miao et al. 2018); and the San Joaquin and Salt Lake Basins, United States (Whiteman et al. 2014; Zhang et al. 2020)]. These episodes may last from several days to several weeks and often arise due to the development of persistent cold-air pools (PCAPs), within which lateral and vertical mixing are inhibited due to sheltering by surrounding topography and a stable temperature profile (Dorninger et al. 2011; Reeves et al. 2011; Lareau et al. 2013; Sheridan et al. 2014; Holmes et al. 2015; Sun and Holmes 2019; Ivey et al. 2019; Sun et al. 2020). While a number of field campaigns targeting either wintertime basin meteorology (e.g., Lareau et al. 2013; McCaffrey et al. 2019) or wintertime pollution chemistry (e.g., Brown et al. 2013; Franchin et al. 2018; Young et al. 2016) have been conducted in the United States, only a few of these campaigns have explicitly considered coupling between interconnected chemical and meteorological processes (e.g., Baasandorj et al. 2017; Prabhakar et al. 2017; Salvador et al. 2021). The upcoming Alaskan Pollution and Chemical Analysis (ALPACA) is specifically targeting this knowledge gap in cold and dark conditions.

Current gaps in our understanding of the coupled chemical–meteorological interactions that result in high-pollution events in many basins worldwide make identification of the most effective air-basin specific emission control strategies challenging. Meteorological processes (thermodynamic, radiative, and dynamical) influence both pollution accumulation, dispersion, and transport and aerosol pollution chemistry, while chemical processes in turn influence radiative transfer, cloud formation, and mixing processes. Figure 1 presents a graphical illustration of some of the coupled chemical–meteorological processes that occur in basins. Some key meteorological processes that control the formation, duration, and breakdown of PCAPs include synoptic drivers such as high pressure and associated subsidence, which can precipitate elevated thermal inversions; warm air advection aloft and large-scale winds and turbulent mixing, alongside local drivers such as the surface energy and radiation budget, which strongly influence formation and dissipation of surface-based thermal inversions; characteristics of the underlying surface (e.g., snow cover, water, urban or non-urban landscape); low clouds and fog; and local boundary layer flows near the surface. In turn, the location and types of urban emissions, aerosol formation and growth processes, and chemical cycling processes influence and are influenced by the ambient meteorology (Fig. 1). The unique basin topography (e.g., slope, how enclosed the basin is, and the size of basin) also play an important role in modulating the rate of pollutant buildup and vertical profiles of temperature and moisture. The interactions between these numerous meteorological processes regulating the frequency, location, and speed of chemical processes in PCAPs, and complex wintertime chemistry, has not yet been observed with sufficient detail to provide satisfactory understanding of these complex pollution episodes and their evolution in time and space

Fig. 1.