Understanding sources of atmospheric hydrogen chloride in coastal spring and continental winter

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Date

2021-08-18

Authors

Angelucci, Angela A.
Furlani, Teles
Wang, Xuan
Jacob, Daniel J.
VandenBoer, Trevor
Young, Cora

Journal Title

Journal ISSN

Volume Title

Publisher

ACS Publications

Abstract

Ambient 0.5 Hz hydrogen chloride (HCl) measurements were made in Canadian cities to 17 investigate chlorine activation and constrain the tropospheric chlorine budget. Springtime HCl mixing ratios in a coastal city (St. John’s, NL) were up to 1200 parts per trillion by volume (pptv) with median of 63 pptv and were consistently elevated during daytime. High-time resolution measurements allowed attribution of events to general sources, including direct emissions. Most coastal HCl was related to sea salt aerosol acid displacement (R1) and chlorine activation. Continental urban (Toronto, ON) wintertime HCl mixing ratios reached up to 541 and 172 pptv, with medians of 67 and 11 pptv during two sampling periods characterized by different wind directions. The absence of consistent relationships with NOx, temperature, and wind direction, as well as a lack of diurnal patterns, suggested uncharacterized direct sources of HCl. One period with road salting occurred during sampling, but no relationship to changes in HCl observations was found. The contribution of road salt to the measured HCl may have been masked by larger contributors (such as direct sources of HCl) or perhaps the relationship between HCl and road salt application is not immediate and thus additional measurements over multiple salting events or between seasons would be required. GEOS-Chem modelled HCl temporal variations in mixing ratio agreed well with coastal measurements only. Measured mixing ratios were underestimated by the model in both locations, but to a greater degree (up to 3 orders of magnitude) in the continental city. The discrepancy between the model and measurements for the continental wintertime city emphasizes the need for greater understanding of direct sources of HCl and the impact of road salt.

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Keywords

Hydrogen chloride, Reactive chlorine, Cavity ring-down spectroscopy, GEOS-Chem, Emissions, Marine, Continental, Wintertime, Road salt

Citation

Angelucci, A.A.; Furlani, T. C.; Wang, X.; Jacob, D. J.; VandenBoer, T. C.; Young, C. J. Understanding sources of atmospheric hydrogen chloride in coastal spring and continental winter. ACS Earth Space Chem. 2021, 5, 2507−2516. https://doi.org/10.1021/acsearthspacechem.1c00193