Browsing by Author "Herndon, Scott C."

Now showing 1 - 2 of 2

Ground-based investigation of HO<sub><i>x</i></sub> and ozone chemistry in biomass burning plumes in rural Idaho
(Copernicus GmbH, 2022-04) Lindsay, Andrew J.; Anderson, Daniel C.; Wernis, Rebecca A.; Liang, Yutong; Goldstein, Allen H.; Herndon, Scott C.; Roscioli, Joseph R.; Dyroff, Christoph; Fortner, Ed C.; Croteau, Philip L.; Majluf, Francesca; Krechmer, Jordan E.; Yacovitch, Tara I.; Knighton, Walter B.; Wood, Ezra C.
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, evident by ozone enhancement ratios (ΔO3/ΔCO) that ranged up to 0.06 ppbv ppbv−1. [XO2] was similarly elevated during some BB events. Overall, instantaneous ozone production rates (P(O3)) were minimally 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 Master Chemical Mechanism (MCM) and GEOS-Chem mechanisms overall and during periods of BB influence. The models consistently overestimated XO2 with the base MCM and GEOS-Chem XO2 predictions high by an average of 28 % and 20 %, respectively. 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 unmeasured HOx sources. To the best of our knowledge, this is the first BB study featuring peroxy radical measurements.
Oxygenated Aromatic Compounds are Important Precursors of Secondary Organic Aerosol in Biomass-Burning Emissions
(2020) Akherati, Ali; He, Yicong; Coggon, Matthew M.; Koss, Abigail; Hodshire, Anna; Sekimoto, Kanako; Warneke, Carsten; de Gouw, Joost A.; Yee, Lindsay D.; Seinfeld, John H.; Onasch, Timothy B.; Herndon, Scott C.; Knighton, Walter B.; Cappa, Christopher David; Kleeman, Michael J.; Yim, Christopher Y.; Kroll, Jesse H.; Pierce, Jeffrey R.; Jathar, Shantanu H.
Biomass burning is the largest combustion-related source of volatile organic compounds (VOCs) to the atmosphere. We describe the development of a state-of-the-science model to simulate the photochemical formation of secondary organic aerosol (SOA) from biomass-burning emissions observed in dry (RH <20%) environmental chamber experiments. The modeling is supported by (i) new oxidation chamber measurements, (ii) detailed concurrent measurements of SOA precursors in biomass-burning emissions, and (iii) development of SOA parameters for heterocyclic and oxygenated aromatic compounds based on historical chamber experiments. We find that oxygenated aromatic compounds, including phenols and methoxyphenols, account for slightly less than 60% of the SOA formed and help our model explain the variability in the organic aerosol mass (R2 = 0.68) and O/C (R2 = 0.69) enhancement ratios observed across 11 chamber experiments. Despite abundant emissions, heterocyclic compounds that included furans contribute to ∼20% of the total SOA. The use of pyrolysis-temperature-based or averaged emission profiles to represent SOA precursors, rather than those specific to each fire, provide similar results to within 20%. Our findings demonstrate the necessity of accounting for oxygenated aromatics from biomass-burning emissions and their SOA formation in chemical mechanisms.