Dataset Information

Observation of Road Salt Aerosol Driving Inland Wintertime Atmospheric Chlorine Chemistry.

ABSTRACT: Inland sources of particulate chloride for atmospheric nitryl chloride (ClNO2) formation remain unknown and unquantified, hindering air quality assessments. Globally each winter, tens of millions of tons of road salt are spread on roadways for deicing. Here, we identify road salt aerosol as the primary chloride aerosol source, accounting for 80-100% of ClNO2 formation, at an inland urban area in the wintertime. This study provides experimental evidence of the connection between road salt and air quality through the production of this important reservoir for nitrogen oxides and chlorine radicals, which significantly impact atmospheric composition and pollutant fates. A numerical model was employed to quantify the contributions of chloride sources to ClNO2 production. The traditional method for simulating ClNO2 considers chloride to be homogeneously distributed across the atmospheric particle population; yet, we show that only a fraction of the particulate surface area contains chloride. Our new single-particle parametrization considers this heterogeneity, dramatically lowering overestimations of ClNO2 levels that have been routinely reported using the prevailing methods. The identification of road salt as a ClNO2 source links this common deicing practice to atmospheric composition and air quality in the urban wintertime environment.

SUBMITTER: McNamara SM

PROVIDER: S-EPMC7256959 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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Observation of Road Salt Aerosol Driving Inland Wintertime Atmospheric Chlorine Chemistry.

McNamara Stephen M SM Kolesar Katheryn R KR Wang Siyuan S Kirpes Rachel M RM May Nathaniel W NW Gunsch Matthew J MJ Cook Ryan D RD Fuentes Jose D JD Hornbrook Rebecca S RS Apel Eric C EC China Swarup S Laskin Alexander A Pratt Kerri A KA

ACS central science 20200513 5

Inland sources of particulate chloride for atmospheric nitryl chloride (ClNO<sub>2</sub>) formation remain unknown and unquantified, hindering air quality assessments. Globally each winter, tens of millions of tons of road salt are spread on roadways for deicing. Here, we identify road salt aerosol as the primary chloride aerosol source, accounting for 80-100% of ClNO<sub>2</sub> formation, at an inland urban area in the wintertime. This study provides experimental evidence of the connection bet ...[more]

PMID: 32490185

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Project description:As sources of reactive halogens, snowpacks in sea ice regions control the oxidative capacity of the Arctic atmosphere. However, measurements of snowpack halide concentrations remain sparse, particularly in the high Arctic, limiting our understanding of and ability to parameterize snowpack participation in tropospheric halogen chemistry. To address this gap, we measured concentrations of chloride, bromide, and sodium in snow samples collected during polar spring above remote multi-year sea ice (MYI) and first-year sea ice (FYI) north of Greenland and Alaska, as well as in the central Arctic, and compared these measurements to a larger dataset collected in the Alaskan coastal Arctic by Krnavek et al. (2012). Regardless of sea ice region, these surface snow samples generally featured lower salinities, compared to coastal snow. Surface snow in FYI regions was typically enriched in bromide and chloride compared to seawater, indicating snowpack deposition of bromine and chlorine-containing trace gases and an ability of the snowpack to participate further in bromine and chlorine activation processes. In contrast, surface snow in MYI regions was more often depleted in bromide, indicating it served as a source of bromine-containing trace gases to the atmosphere prior to sampling. Measurements at various snow depths indicate that the deposition of sea salt aerosols and halogen-containing trace gases to the snowpack surface played a larger role in determining surface snow halide concentrations compared to upward brine migration from sea ice. Calculated enrichment factors for bromide and chloride, relative to sodium, in the MYI snow samples suggests that MYI regions, in addition to FYI regions, have the potential to play an active role in Arctic boundary layer bromine and chlorine chemistry. The ability of MYI regions to participate in springtime atmospheric halogen chemistry should be considered in regional modeling of halogen activation and interpretation of satellite-based tropospheric bromine monoxide column measurements.

Dataset Information

Observation of Road Salt Aerosol Driving Inland Wintertime Atmospheric Chlorine Chemistry.

Publications

Observation of Road Salt Aerosol Driving Inland Wintertime Atmospheric Chlorine Chemistry.

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