Emission factors of long-lived volatile organic compounds from the 2019–2020 Australian wildfires during the COALA campaign

Abstract

Abstract. In 2019/2020, Australia experienced its largest wildfire season on record. Smoke covered hundreds of square kilometers across the southeastern coast and reached the site of the 2020 COALA (Characterizing Organics and Aerosol Loading over Australia) field campaign in New South Wales. Using a subset of nighttime observations made by a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS), we calculate emission ratios (ERs) and factors (EFs) for 21 volatile organic compounds (VOCs). We restrict our analysis to VOCs with sufficiently high lifetimes to be minimally impacted by oxidation over the ~8 h between when the smoke was emitted and when it arrived at the field site. We use oxidized VOC to VOC ratios to assess the total amount of radical oxidation: maleic anhydride/furan to assess OH oxidation, and (cis-2-butenediol + furanone)/furan to assess NO3 oxidation. We compare ERs calculated from the freshest portion of the plume to ERs calculated using the entire nighttime period. Finding good agreement between the two, we are able to extend our analysis to VOCs measured in more chemically aged portions of the plume. Our analysis provides ERs and EFs for 9 compounds not previously reported for temperate forests in Australia: acrolein, pentanones/methylbutanal, methyl propanoate, methyl methacrylate, propene, maleic anhydride, benzaldehyde, methyl guaiacol, and methylbenzoic acid. We compare our results with two studies in similar Australian biomes, and two studies focused on US temperate forests. We find mixed agreement for EFs presented from previous studies of Australian wildfires, and generally good agreement with studies focused on fires in the Western US. This suggests that comprehensive field measurements of biomass burning VOC emissions in other regions may be applicable to Australian temperate forests.

Parameterizations of US wildfire and prescribed fire emission ratios and emission factors based on FIREX-AQ aircraft measurements

“…Numerous studies have quantified emission factors (EFs; grams emitted per kg of dry fuel burned) for various fuel types and different fire characteristics using ground-based or airborne measurements in close proximity to wildland/prescribed fire plumes (e.g., Stockwell et al, 2016;Liu et al, 2017;Peng et al, 2020;Mouat et al, 2021;Permar et al, 2021) or controlled laboratory burns (e.g., Stockwell et al, 2014;Koss et al, 2018;Selimovic et al, 2018). Literature reviews to combine these results have been periodically conducted (Andreae and Merlet, 2001;Akagi et al, 2011;Andreae, 2019), with the most recent by Prichard et al (2020).…”

Fuel-Type Independent Parameterization of Volatile Organic Compound Emissions from Western US Wildfires

“…Numerous studies have quantified emission ratios and emission factors for various fuel types across burn conditions using field measurements from wildland and prescribed fires − or laboratory measurements from simulated burns. − Literature reviews have been periodically conducted to consolidate these results and provide recommended emission factors that can be applied to atmospheric models. − Nevertheless, uncertainties in the process-level understanding and model representation of fire emissions, plume rise, and chemistry still exist, which makes it difficult to accurately predict the VOC composition of primary biomass burning emissions in models. This can be caused by an insufficient understanding of the chemistry and total emissions of VOCs across fuel types, ecosystems, and/or fire combustion conditions. − VOC emissions from biomass burning are described by multiple complex processes that often occur simultaneously, e.g., distillation, pyrolysis, flaming, and smoldering combustion processes. − The relative importance of each process can change over the course of a fire and modulate the relative distribution of VOC emissions spatially and temporally and also relates to the variability in integrated VOC emissions between different fires.…”

“…Numerous studies have quantified emission ratios and emission factors for various fuel types across burn conditions using field measurements from wildland and prescribed fires 14 − 20 or laboratory measurements from simulated burns. 21 − 23 Literature reviews have been periodically conducted to consolidate these results and provide recommended emission factors that can be applied to atmospheric models.…”