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Abstract Title: Observations of High Oxidized Mercury from Storm Peak Laboratory Using an Improved Dual-Channel Measurement System
Presenter Name: Lynne Gratz
Company/Institution: Colorado College
Session: Special Session - New developments in understanding reactive mercury concentrations and chemistry
Day and Session: Thursday 28th July - Session Four
Start Time: 15:00 UTC
Co-Authors: Lynne Gratz,Zoe Zwecker,Brandon Chan,Seth Lyman,Tyler Elgiar,A. Gannet Hallar,Noah Hirshron,Rainer Volkamer,Christopher Lee

Abstract Information :

The fate of atmospheric mercury (Hg) depends strongly on dynamic cycling between its elemental (Hg0) and oxidized (HgII) forms. Yet, uncertainties persist around the atmospheric oxidation chemistry, both in terms of the leading oxidant(s) and the underlying chemical kinetics. Bromine-initiated oxidation has been observed in environments such as the marine boundary layer, subtropical free troposphere, and polar regions, while recent modeling work suggests that the hydroxyl radical may also initiate atmospheric Hg oxidation. Accurate observations of atmospheric Hg and it potential oxidants remain limited, inhibiting a quantitative understanding of Hg cycling and fate. From March to October 2021, we operated an improved dual-channel Hg measurement system at the high elevation Storm Peak Laboratory (SPL) in Steamboat Springs, CO (3220 m AMSL) to investigate the sources and chemistry of Hg0 and HgII in a continental atmosphere. Criteria gases, radon, aerosol properties and concentration, halogens and other reactive gases, and meteorological variables were concurrently measured. We identified four multi-day episodes of enhanced HgII with mean (ñ 1?) hourly concentrations ranging from 104 ñ 24 to 157 ñ 35 pg m-3 and a maximum hourly concentration of 253 pg m-3. Elemental Hg was simultaneously depleted and anti-correlated with HgII (R = -0.7 to -0.9). The sampled air masses were generally dry (RH < 40%) and anthropogenic pollutant concentrations were also low. These episodes were similar in nature, but with approximately two times higher HgII concentrations, compared to an earlier spring-summer study at SPL that used a KCl-denuder system. A principal components factor analysis augmented our episodic analysis, suggesting that HgII was strongly negatively associated with Hg0 and atmospheric water vapor, consistent with free tropospheric oxidation as the primary HgII source. Similar measurements will be collected at SPL from March ? August 2022, and will be included in this presentation to the extent possible.

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