Preprints
https://doi.org/10.5194/egusphere-2024-3272
https://doi.org/10.5194/egusphere-2024-3272
29 Oct 2024
 | 29 Oct 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Hydrogen Peroxide Photoformation in Particulate Matter and its Contribution to S(IV) Oxidation During Winter in Fairbanks, Alaska

Michael Oluwatoyin Sunday, Laura Marie Dahler Heinlein, Junwei He, Allison Moon, Sukriti Kapur, Ting Fang, Kasey C. Edwards, Fangzhou Guo, Jack Dibb, James H. Flynn III, Becky Alexander, Manabu Shiraiwa, and Cort Anastasio

Abstract. The high levels of sulfate in wintertime particles in Fairbanks, Alaska are a subject of keen research interest and regulatory concern. Recent results from the 2022 ALPACA (Alaska Layered Pollution And Chemical Analysis) field campaign indicate that roughly 40 % of wintertime sulfate in Fairbanks is secondary, with hydrogen peroxide (HOOH) the dominant oxidant. Since formation of HOOH in the gas phase should be negligible during ALPACA because of high levels of NOx, we examined whether reactions within particles could be a significant source of HOOH. To test this, we collected particulate matter (PM) samples during the ALPACA campaign, extracted them, illuminated them with simulated sunlight, and measured HOOH production. Aqueous extracts showed significant light absorption, a result of brown carbon (BrC) from sources such as residential wood combustion. Photoformation rates of HOOH in the PM extracts (normalized to Fairbanks winter sunlight) range from 6 to 71 µM hr-1. While light absorption is nearly independent of pH, HOOH formation rates decrease with increasing pH. Extrapolating to the concentrated conditions of aerosol liquid water (ALW) gives an average rate of in-particle HOOH formation of ~ 0.1 M hr-1. Corresponding rates of sulfate formation from particle-produced HOOH are 0.05 – 0.5 µg m-3 hr-1, accounting for a significant portion of the secondary sulfate production rate. Our results show that HOOH formed in particles is an important contribution to sulfate formation in ambient wintertime particles, even under the low actinic flux conditions typical of winter in subarctic locations like Fairbanks.

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Michael Oluwatoyin Sunday, Laura Marie Dahler Heinlein, Junwei He, Allison Moon, Sukriti Kapur, Ting Fang, Kasey C. Edwards, Fangzhou Guo, Jack Dibb, James H. Flynn III, Becky Alexander, Manabu Shiraiwa, and Cort Anastasio

Status: open (until 10 Dec 2024)

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Michael Oluwatoyin Sunday, Laura Marie Dahler Heinlein, Junwei He, Allison Moon, Sukriti Kapur, Ting Fang, Kasey C. Edwards, Fangzhou Guo, Jack Dibb, James H. Flynn III, Becky Alexander, Manabu Shiraiwa, and Cort Anastasio
Michael Oluwatoyin Sunday, Laura Marie Dahler Heinlein, Junwei He, Allison Moon, Sukriti Kapur, Ting Fang, Kasey C. Edwards, Fangzhou Guo, Jack Dibb, James H. Flynn III, Becky Alexander, Manabu Shiraiwa, and Cort Anastasio

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Short summary
Hydrogen peroxide (HOOH) is an important oxidant that forms atmospheric sulfate. We demonstrate that illumination of brown carbon can rapidly form HOOH within particles, even under the low sunlight conditions of Fairbanks, Alaska during winter. This in-particle formation of HOOH is fast enough that it forms sulfate at significant rates. In contrast, the formation of HOOH in the gas phase during the campaign is expected to be negligible because of high NOx levels.