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Abstract. Furanoids are significant contributors to volatile organic compound hydroxyl radical reactivity in biomass burning emissions, yet their accurate measurement using proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) remains challenging due to potential interferences and measurement uncertainties. In this study, we conduct detailed laboratory characterizations of furan (C4H4O, protonated m/z 69.033), 2(3H)-furanone (C4H4O2, m/z 85.028), 2-furaldehyde (C5H4O2, m/z 97.028), 2,5-dimethylfuran (C6H8O, m/z 97.065), and maleic anhydride (C4H2O3, m/z 99.008). Sensitivities for these compounds were found to have minimal dependence (less than 15 %) on both sample humidity and drift tube electric field strength (E/N). At high E/N (150 Td), fragmentation was observed for 2-furaldehyde (∼ 8 %) at m/z 69.033, potentially interfering furan measurements, while hydrolysis products corresponding to m/z+18 ions were detected for 2(3H)-furanone, 2-furaldehyde, and maleic anhydride. The hydrolysis of maleic anhydride to maleic acid is most prominent, with the hydrate accounting for 7 %–31 % of the parent ion signal across E/N conditions. Gas standard recertification confirmed the long-term stability of furanoids, and 21 other VOCs, in compressed gas mixtures, with changes in mixing ratios of less than 5 % over seven years, although PTR-ToF-MS instrument sensitivities decreased by ∼ 30 % during this time, likely due to aging of the microchannel plate (MCP). While the stability of gas standards and the minimal humidity and fragmentation effects support the accurate measurement of furanoids by PTR-ToF-MS, discrepancies with co-deployed gas chromatography-mass spectrometry highlight the need to further investigate potential isomeric and fragment interferences, particularly in aged BB smoke. 

Quantifying the variable impacts of wildfire smoke on ozone air quality is challenging. Here we use airborne measurements from the 2018 Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) to parameterize emissions of reactive nitrogen (NOy) from wildfires into peroxyacetyl nitrate (PAN; 37%), NO3− (27%), and NO (36%) in a global chemistry-climate model with 13 km spatial resolution over the contiguous US. The NOy partitioning, compared with emitting all NOy as NO, reduces model ozone bias in near-fire smoke plumes sampled by the aircraft and enhances ozone downwind by 5–10 ppbv when Canadian smoke plumes travel to Washington, Utah, Colorado, and Texas. Using multi-platform observations, we identify the smoke-influenced days with daily maximum 8-hr average (MDA8) ozone of 70–88 ppbv in Kennewick, Salt Lake City, Denver and Dallas. On these days, wildfire smoke enhanced MDA8 ozone by 5–25 ppbv, through ozone produced remotely during plume transport and locally via interactions of smoke plume with urban emissions. 

The first 5 hours of aging in biomass burning plumes can strongly affect ozone photochemistry. We examine how volatile organic compounds (VOCs), nitrogen oxides, and nitrous acid influence hydroxyl radical, ozone, and peroxyacetyl nitrate (PAN) based on three aircraft campaigns over the United States. Our analyses reveal variable, highly elevated hydroxyl radical concentrations in the first 2 hours, resulting in evident fire-to-fire variability in VOCs oxidation and in ozone and PAN production. About 40 to 70% of the variability is explained by chemical aging. Ozone production in the plumes is usually VOC-limited for the first 2 hours and then nitrogen oxide limited downwind. Box model results for hydroxyl radical, ozone, and most VOCs, using the full, explicit Master Chemical Mechanism (MCM) mechanism, suggest no major gaps in the current best knowledge of gas-phase chemistry. However, the MCM sometimes overestimates PAN due to underestimated nitrogen oxide sinks. GEOS-Chem, a widely used chemical transport model with a reduced mechanism, generally underperforms because of incomplete VOC representation. We identify these critical pathways to guide future model development. 

Abstract We present measurements of volatile organic compounds (VOCs) and other trace gases taken in Salt Lake City, Utah in August and September 2022. As part of the Salt Lake regional Smoke, Ozone and Aerosol Study (SAMOZA), 35 VOCs were measured with two methods: a proton‐transfer‐reaction time‐of‐flight mass spectrometer (PTR‐ToF‐MS) and 2,4‐dinitrophenylhydrazine (DNPH) cartridges analyzed by high‐performance liquid chromatography (HPLC). Over two months, the total measured VOCs averaged 32 ± 24 ppb (mean ± standard deviation) with the hourly maximum at 141 ppb, and the total calculated OH reactivity averaged 3.7 ± 3.0 s⁻¹(maximum at 20.7 s⁻¹). Among them, methanol and ethanol were the most abundant VOCs, making up 42% of the ambient mixing ratio. Isoprene and monoterpenes contributed 25% of the OH reactivity from VOCs, while formaldehyde and acetaldehyde made up another 30%. The positive matrix factorization analysis showed 5 major sources of VOCs, with 32% of abundance being attributed to secondary production/biogenic sources, 44% from the combination of traffic and personal care products, 15% from industrial solvent use, and the rest from biomass burning (10%). Moderate smoke‐impacted days elevated various hazardous air pollutants (HAPs) on average by 45%–217% compared to smoke‐free days. The ratio of OH reactivity from NO_xto that from VOCs showed that ozone production was mostly VOC‐limited throughout the campaign, consistent with our modeling study. VOCs and NO_xboth showed increased OH reactivity due to smoke influence. NO_xfeatured increased reactivity on weekdays compared to weekends, an effect not shown for VOC reactivity during SAMOZA. 

Abstract We investigated how various sources contributed to observations of over 40 trace gas and particulate species in a typical Fairbanks residential neighborhood during the Alaskan Layered Pollution and Chemical Analysis campaign in January–February 2022. Aromatic volatile organic compounds (VOCs) accounted for ∼50% of measured VOCs (molar ratio), while methanol and ethanol accounted for ∼34%. The total wintertime VOC burden and contribution from aromatics were much higher than other US urban areas. Based on diel cycles and positive matrix factorization (PMF) analyses, we find traffic was the largest source of NO, CO, black carbon, and aromatic VOCs. Formic and acetic acid, hydroxyacetone, furanoids, and other VOCs were primarily attributed to residential wood combustion (RWC). Formaldehyde was one of several VOCs featuring significant contributions from multiple sources: RWC (∼35%), aging (∼30%), traffic (∼21%), and heating oil combustion (HO, ∼14%). PMF solutions assigned primary fine particulate matter to RWC (10%–30%), traffic (25%–40%), and HO (30%–60%), the latter likely reflecting high sulfur emissions from older furnaces and fast secondary chemistry. Despite cold and dark conditions, secondary processes impacted many trace gas and particle species' budget by ±10%–20% and more in some cases. Transport of O₃‐rich regional air into Fairbanks contributed to aging, specifically NO₃radical formation. This work highlights a long‐term trend observed in Fairbanks: increasing traffic and decreasing RWC relative contributions as total pollution decreases. Fairbanks exports a relatively fresh pollutant mixture to the regional arctic, the fate of which warrants future study. 

Rapid production of formic acid in biomass burning smoke is not captured by the Master Chemical Mechanism (MCM) nor simplified GEOS-Chem chemistry, likely due to missing secondary chemical production.