Ground-based investigation of HO<sub><i>x</i></sub> and ozone chemistry in biomass burning plumes in rural Idaho

Abstract

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, 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.

Gas–particle partitioning of semivolatile organic compounds when wildfire smoke comes to town

“…These air masses contained fire emissions from mainly oak woodland land-scapes, combined with suburban housing developments, and agricultural areas. Our SV-TAG measurements were conducted on the University of California (UC) Berkeley campus (37 • 52 24.5 N, 122 Lindsay et al (2022). Backward trajectory analysis by Lindsay et al (2022) suggests that the smoke plumes traveled at least 3-5 h and up to 18-30 h prior to arriving at this site.…”

“…Our SV-TAG measurements were conducted on the University of California (UC) Berkeley campus (37 • 52 24.5 N, 122 Lindsay et al (2022). Backward trajectory analysis by Lindsay et al (2022) suggests that the smoke plumes traveled at least 3-5 h and up to 18-30 h prior to arriving at this site.…”

Investigation of Ozone Formation Chemistry during the Salt Lake Regional Smoke, Ozone, and Aerosol Study (SAMOZA)

“…The heterogeneous uptake of hydroxyl radical (OH) and hydroperoxyl radical (HO 2 ) onto aerosols was included based on previous studies (eq ): , normald X / normald t = prefix− 0.25 × γ × c ( X ) × PM 2.5 × SA specific × X g × 10 − 6 where d X /d t is the heterogeneous loss rate of OH or HO 2 in ppb s –1 , γ is the aerosol uptake coefficient, c( X ) is the average molecular speed of OH or HO 2 in m s –1 , PM 2.5 has units of μg m –3 , SA specific is the specific aerosol surface area in m 2 g –1 , and X g is the concentration of OH or HO 2 in ppb that is in the gas phase. γ was assumed to be 0.2, following Jacob and Slade and Knopf .…”

“…77 Then, the modelcalculated photolysis rates were scaled in reference to the J NOd 2 values calculated from eq 2. The heterogeneous uptake of hydroxyl radical (OH) and hydroperoxyl radical (HO 2 ) onto aerosols was included based on previous studies (eq 3): 78,79…”

“…81 Molecular weight and temperature were used to determine c(X). SA specific was assumed to be 4 m 2 g −1 , following Lindsay et al 79 Collectively, our treatment of photolysis rates and heterogeneous uptake of OH and HO 2 onto aerosols had an important effect on model-predicted O 3 , which will be discussed in the next section.…”