A225-0001
Influences of Solar Irradiation and Aerosol Surface Area on Nitrous Acid Production in Western U.S. Wildfire Smoke

Wednesday, 16 December 2020
Poster
Jackson Kaspari1, Eric M Scheuer2, Jiajue Chai3, Meredith Galanter Hastings3, Bruce E Anderson4, Carolyn E Jordan5 and Jack E Dibb6, (1)University of New Hampshire Main Campus, Department of Chemistry, Durham, NH, United States, (2)University of New Hampshire, Institute for the Study of Earth, Ocean, and Space, Durham, NH, United States, (3)Brown University, Department of Earth, Environmental and Planetary Sciences, and Institute at Brown for Environment and Society, Providence, RI, United States, (4)NASA Langley Research Center, Hampton, VA, United States, (5)National Institute of Aerospace, Hampton, VA, United States, (6)University of New Hampshire Main Campus, Institute for the Study of Earth, Ocean, and Space, Durham, NH, United States
Abstract:
Biomass burning has been identified as a primary emission source for a host of gas and aerosol-phase compounds, which can damage environmental and human health. During FIREX-AQ, collaborators from UNH, NASA Langley Aerosol Research Group Experiment (LARGE), and Brown University, measured wildfire emissions onboard NASA Langley’s mobile laboratory during July and August of 2019. Nitrous acid (HONO) and nitric acid (HNO3) concentrations were measured at nominal 5-minute resolution using a dual mist chamber-ion chromatograph system resulting in approximately 1,200 total samples from five separate fires in the western US. Enhancement ratios between PM2.5 and carbon monoxide were used to discriminate between young and aged smoke plumes. Average HONO concentrations were significantly higher (P < 0.01) in young daytime smoke compared to young nighttime smoke, while no statistical differences (P > 0.05) were observed between young and aged smoke during day or night. In daytime smoke from the Williams Flats fire (75 km SE of Spokane, WA on the Columbia River) UV-A irradiation was highly correlated (R2 = 0.94, P < 0.01) with HONO to nitrogen dioxide (NO2) ratios; indicating that heterogeneous NO2 to HONO conversion more than compensated for rapid photolytic loss of HONO. Black carbon (BC) may serve as a stable proxy for total available aerosol surface area in biomass burning plumes when total aerosol size distributions are unavailable. During the day, HONO/NO2 variability was well predicted by BC abundance (R2 = 0.97, P = 0.11), when the abundance exceeds 1 µg/m3. However, at lower BC concentrations there was no strong correlation with HONO/NO2. At night, this relationship was stronger (R2 = 0.96, P = 0.02), partly due to consistently high BC concentrations. These observations suggest that heterogeneous conversion of NO2 to HONO on aerosol is a significant source of HONO in dense smoke plumes. In more diffuse smoke, conversion on other surfaces (soil, foliage and dust) likely become more important.
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