Vertical distribution of pollution trapped by wintertime surface inversions in Fairbanks, Alaska, during the ALPACA experiment
- 1University of California, Los Angeles (Los Angeles, United States of America)
Abstract
Air pollution in cold wintertime urban areas is a ubiquitous problem. Surface temperature inversions under low wind conditions and surface emissions lead to the formation of a shallow polluted surface layer (PSL). The presence of this PSL is well documented, but its height, the rates of exchange with the background atmosphere, and the interplay between vertical mixing and chemistry remain poorly quantified. Here we provide quantitative insights into this coupled chemistry-transport system using observations and modeling of vertical pollutant profiles. Long-path Differential Optical Absorption Spectroscopy of vertical trace gas profiles during the 2022 Alaskan Layered Pollution and Chemical Analysis (ALPACA) experiment in Fairbanks, Alaska, quantitatively track the frequent establishment of PSLs with heights of 20–40 m, which sometimes persist for several days. PSL trace gas mixing ratios often plateau at levels of up to 35 ppb SO ₂ , 60 ppb NO ₂ , 2.5 ppb HONO, 7 ppb HCHO, and low ozone as a result of surface emissions, gas-phase chemistry, and ineffective mixing with the background atmosphere. Parameterizing vertical mixing with observed surface temperature gradients and wind speed in the PACT-1D chemistry and transport model leads to excellent agreement of modeled and measured trace gas profiles. The PACT-1D transport scheme determines the residence time of pollutants within the PSL to be 1–4 h, confirming the strong influence of atmospheric mixing on the composition of sustained PSL events. Altitude-dependent ozone and NO x chemistry highlight the strong coupling between mixing and chemistry, which must be considered to quantify pollutant concentrations accurately in shallow PSLs.
Versions
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BibTeX
@article{stutz2026vertical,
title = {{Vertical distribution of pollution trapped by wintertime surface inversions in Fairbanks, Alaska, during the ALPACA experiment}},
author = {Jochen Stutz and Jonas Kuhn and Sol Cooperdock and Sarah Johnson and Fangzhou Guo and James H. Flynn and Meeta Cesler-Maloney and William R. Simpson},
journal = {Atmospheric Chemistry and Physics},
year = {2026},
month = oct,
doi = {10.5194/acp-26-14345-2026},
url = {https://acp.copernicus.org/articles/26/14345/2026/},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Vertical distribution of pollution trapped by wintertime surface inversions in Fairbanks, Alaska, during the ALPACA experiment
AU - Jochen Stutz
AU - Jonas Kuhn
AU - Sol Cooperdock
AU - Sarah Johnson
AU - Fangzhou Guo
AU - James H. Flynn
AU - Meeta Cesler-Maloney
AU - William R. Simpson
PY - 2026
DA - 2026/10/12
JO - Atmospheric Chemistry and Physics
DO - 10.5194/acp-26-14345-2026
UR - https://acp.copernicus.org/articles/26/14345/2026/
AB - Air pollution in cold wintertime urban areas is a ubiquitous problem. Surface temperature inversions under low wind conditions and surface emissions lead to the formation of a shallow polluted surface layer (PSL). The presence of this PSL is well documented, but its height, the rates of exchange with the background atmosphere, and the interplay between vertical mixing and chemistry remain poorly quantified. Here we provide quantitative insights into this coupled chemistry-transport system using observations and modeling of vertical pollutant profiles. Long-path Differential Optical Absorption Spectroscopy of vertical trace gas profiles during the 2022 Alaskan Layered Pollution and Chemical Analysis (ALPACA) experiment in Fairbanks, Alaska, quantitatively track the frequent establishment of PSLs with heights of 20–40 m, which sometimes persist for several days. PSL trace gas mixing ratios often plateau at levels of up to 35 ppb SO ₂ , 60 ppb NO ₂ , 2.5 ppb HONO, 7 ppb HCHO, and low ozone as a result of surface emissions, gas-phase chemistry, and ineffective mixing with the background atmosphere. Parameterizing vertical mixing with observed surface temperature gradients and wind speed in the PACT-1D chemistry and transport model leads to excellent agreement of modeled and measured trace gas profiles. The PACT-1D transport scheme determines the residence time of pollutants within the PSL to be 1–4 h, confirming the strong influence of atmospheric mixing on the composition of sustained PSL events. Altitude-dependent ozone and NO x chemistry highlight the strong coupling between mixing and chemistry, which must be considered to quantify pollutant concentrations accurately in shallow PSLs.
SN - 1680-7324
ER -