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Abstract Title: Ambient Mercury Observations in Wildfire Plumes at Two Western U.S. Sites Using an Improved Dual-Channel Measurement System
Presenter Name: Lynne Gratz
Company/Institution: Colorado College
Session: Special Session - Impacts of Climate Change on Global Mercury Cycling
Co-Authors: Lynne Gratz,Seth Lyman,Tyler Elgiar,Mae Gustin,Sarrah Dunham-Cheatham,A. Gannet Hallar,Noah Hirshron,Rainer Volkamer,Johana Romero

Abstract Information :

Biomass burning releases hazardous air pollutants, including mercury (Hg), to the atmosphere. As wildfires increase in frequency and severity due to climate change, accurately quantifying the concentrations of Hg species in smoke plumes will importantly constrain the potential impacts on ecosystems. Biomass burning emissions are estimated to be predominantly in the elemental form (Hg0). Particulate-bound Hg can also be elevated in smoke plumes, but gaseous oxidized Hg is not thought to be an important component of fire emissions. Meanwhile, most oxidized Hg (HgII) measurements have been conducted at low temporal resolution using measurement systems with well-documented low biases. We collected high temporal resolution measurements of Hg0 and HgII in biomass burning plumes using a dual-channel measurement system from two ground-based stations in the western U.S., the University of Nevada, Reno (1368 m AMSL) and Storm Peak Laboratory (3220 m AMSL) during summers 2020 and 2021, respectively. We used concurrent measurements of criteria gases, aerosol scattering and concentration together with the HMS Fire and Smoke Product and FLEXPART forward trajectories to identify smoke events. Elemental Hg concentrations displayed large, short-term enhancements (> 4 ng m-3) during local (< 25 km) fire events, but were not significantly elevated under the influence of regional smoke as compared to smoke-free air. Elemental Hg and carbon monoxide were strongly correlated in local fire plumes (r2 = 0.6 ? 0.7) with enhancement ratios ranging from 8x10-8 to 4x10-7 ppm Hg:ppm CO, similar to related studies. We detected 10-min HgII concentrations over 500 pg m-3 in local fire plumes at SPL, an unexpected result that demonstrates the importance of high time resolution measurements in transient plumes. Nevertheless, HgII concentrations are calculated by difference method with the dual-channel system, and uncertainties remain in accurately detecting this low concentration, reactive species within rapidly evolving air masses.

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