Formaldehyde evolution in US wildfire plumes during the Fire Influence on Regional to Global Environments and Air Quality experiment (FIREX-AQ)

J Liao ,Steven S Brown,Kirk Ullmann,Aaron Lamplugh,Ilann Bourgeois,Charles H Fite,Caroline C Womack,Dirk Richter,Kanako Sekimoto,Alan Fried,Georgios I Gkatzelis,John B Nowak,Matthew M Coggon,Reem A Hannun,Thomas B Ryerson,Samuel R Hall,Christopher D Holmes,Anxhelo Agastra,Petter Weibring,Vanessa Selimovic,R A Washenfelder ,Michael Robinson ,J P Digangi ,C Warneke ,Hannah Halliday ,J M St Clair ,R S Hornbrook ,E C Apel ,J Peischl ,J B Gilman ,G S Diskin ,G M Wolfe ,P R Veres ,T F Hanisco ,J A Neuman

doi:10.5194/acp-21-18319-2021

Abstract

Abstract. Formaldehyde (HCHO) is one of the most abundant non-methane volatile organic compounds (VOCs) emitted by fires. HCHO also undergoes chemical production and loss as a fire plume ages, and it can be an important oxidant precursor. In this study, we disentangle the processes controlling HCHO by examining its evolution in wildfire plumes sampled by the NASA DC-8 during the Fire Influence on Regional to Global Environments and Air Quality experiment (FIREX-AQ) field campaign. In 9 of the 12 analyzed plumes, dilution-normalized HCHO increases with physical age (range 1–6 h). The balance of HCHO loss (mainly via photolysis) and production (via OH-initiated VOC oxidation) seems to control the sign and magnitude of this trend. Plume-average OH concentrations, calculated from VOC decays, range from −0.5 (± 0.5) × 106 to 5.3 (± 0.7) × 106 cm−3. The production and loss rates of dilution-normalized HCHO seem to decrease with plume age. Plume-to-plume variability in dilution-normalized secondary HCHO production correlates with OH abundance rather than normalized OH reactivity, suggesting that OH is the main driver of fire-to-fire variability in HCHO secondary production. Analysis suggests an effective HCHO yield of 0.33 (± 0.05) per VOC molecule oxidized for the 12 wildfire plumes. This finding can help connect space-based HCHO observations to the oxidizing capacity of the atmosphere and to VOC emissions.

Highlights

Wildfire biomass burning is a large source of trace gases and aerosols that affect regional atmospheric chemistry, human health, air quality, radiative balance, and climate
Alvarado et al (2020) used TROPOspheric Monitoring Instrument (TROPOMI) data to show that HCHO enhancements in wildfire plumes persist for days downwind
We found that HCHO correlates with CO2 (Fig. S6a in the Supplement) and likely with fire radiative power (FRP) because the change in measured CO2 correlates with the change in FRP (Wiggins et al, 2020)

Summary

Introduction

Wildfire biomass burning is a large source of trace gases and aerosols that affect regional atmospheric chemistry, human health, air quality, radiative balance, and climate. Wildfire emissions of volatile organic compounds (VOCs) are a complex mixture spanning orders of magnitude in concentration, reactivity, and volatility (Gilman et al, 2015; Koss et al, 2018). These VOCs contribute to increased regional tropospheric ozone (Alvarado et al, 2010; Jaffe and Wigder, 2012; Mauzerall et al, 1998; Wotawa and Trainer, 2000) and can deposit onto or evaporate from organic aerosols in biomass burning air masses (Garofalo et al, 2019; Majdi et al, 2019; Palm et al, 2020). HCHO serves as an important source of peroxy radicals (HO2), thereby influencing the formation of ozone and other secondary pollutants (Yokelson et al, 1999)

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Conclusion