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

Abstract

Volatile organic compounds (VOCs) emitted from biomass burning impact air quality and climate. Laboratory studies have shown that the variability in VOC speciation is largely driven by changes in combustion conditions and is only modestly impacted by fuel type. Here, we report that emissions of VOCs measured in ambient smoke emitted from western US wildfires can be parameterized by high-and low-temperature pyrolysis VOC profiles and are consistent with previous observations from laboratory simulated fires. This is demonstrated using positive matrix factorization (PMF) constrained by high-and lowtemperature factors using VOC measurements obtained with a proton-transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) on board the NASA DC-8 during the FIREX-AQ (Fire Influence on Regional and Global Environments and Air Quality) project in 2019. A linear combination of high-and low-temperature factors described more than 70% of the variability of VOC emissions of long-lived VOCs in all sampled wildfire plumes. An additional factor attributable to atmospheric aging was required to parameterize short-lived and secondarily produced VOCs. The relative contribution of the PMF-derived high-temperature factor for a given fire plume was strongly correlated with the fire radiative power (FRP) at the estimated time of emission detected by satellite measurements. By combining the FRP with the fraction of the high-temperature PMF factor, the emission ratios (ERs) of VOCs to carbon monoxide (CO) in fresh wildfires were estimated and agree well with measured ERs (r 2 = 0.80−0.93). KEYWORDS: wildfire, volatile organic compound (VOC), proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), high-temperature pyrolysis, low-temperature pyrolysis, fire radiative power (FRP), FIREX-AQ, positive matrix factorization (PMF)

Impacts on Urban VOCs and PM2.5 during a Wildfire Episode

“…The detailed chemistry of wildfire smoke from different combustible fuels, locations, and temperature profiles needs to be studied further [32]. Different conditions may result in different compounds [37,51], especially for the oxygenated, aged smoke carried over long distances and throughout long fire seasons into heavily populated, urban areas [10].…”

“…Note that the method used in this study was limited by the 76 compounds in our target list. Different wildfire fuel types can generate other VOCs [7,51], which were not detectable with this method. Future work will expand our methods and detection lists for the better characterization of wildfire-generated VOCs.…”