Abstract

Ozone (O3), a potent greenhouse gas that is detrimental to human health, is typically found in elevated concentrations within biomass burning (BB) smoke plumes. The radical species OH, HO2, and RO2 (known collectively as ROx) have central roles in the formation of secondary pollutants including O3 but are poorly characterized for BB plumes. We present measurements of total peroxy radical concentrations ([XO2] ≡ [HO2] + [RO2]) and additional trace-gas and particulate matter measurements from McCall, Idaho during August 2018. There were five distinct periods in which BB smoke impacted this site. During BB events, O3 concentrations were enhanced as evidenced by ozone enhancement ratios (ΔO3/ ΔCO) that ranged up to 0.25 ppbv ppbv−1. [XO2] was similarly elevated during some BB events. Overall, quantified instantaneous ozone production rates (P(O3)) were only slightly impacted by the presence of smoke as NOx enhancements were minimal. Measured XO2 concentrations were compared to zero-dimensional box modeling results to evaluate the effectiveness of the Master Chemical Mechanism (MCM) and GEOS-Chem mechanisms during periods of BB influence and overall agreed within 31 %. One period of BB influence had distinct measured enhancements of 15 pptv XO2 that were not reflected in the model output, likely due to the presence of an unmeasured HOx source, quite likely nitrous acid (HONO). To our knowledge, this is the first BB study featuring peroxy radical measurements.

Highlights

  • Ozone (O3), a potent greenhouse gas that is detrimental to human health, is typically found in elevated concentrations within biomass burning (BB) smoke plumes

  • During BB events, O3 concentrations were enhanced as evidenced by ozone enhancement ratios (ΔO3/ ΔCO) that ranged up to 0.25 ppbv ppbv-1. [XO2]

  • We identify the sources of the observed smoke by pairing NOAA Air Resources Laboratory HYbrid Single Particle Lagrangian

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Summary

Introduction

Unprecedented wildfire activity has been observed in recent years. For example, Brazil’s Amazon rainforest wildfires in and Australia’s bush fires in 2019-2020 were both marked by historically high amounts of land burned. Model suggested peroxy radical concentrations have exhibited a wide range of values (Mason et al, 2001;Parrington et al, 2013;Liu et al, 2016;Baylon et al, 2018), in some cases reaching unrealistically high values ([HO2 + RO2] >> 200 pptv for wildfires in Nova Scotia, Canada as presented in Parrington et al (2013)) This manuscript focuses on smoke observations collected in McCall, Idaho in the Pacific Northwest – a region prone to wildfire – as part of the joint NCAR WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen) and NOAA FIREX (Fire Influence on Regional to Global Environments Experiment) study. Presented are possibly the first measurements of total peroxy radicals in biomass burning plumes, enabling a unique investigation into the impacts of biomass burning on photochemistry and ozone production and the accuracy of commonly used atmospheric chemistry models

Campaign Description
ECHAMP
Additional Measurements
Smoke Events
Calculations
Zero-Dimensional Modeling
Smoke Influence on ozone and its precursors
Ozone Production
Model Evaluation
Conclusions
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