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

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 low-temperature
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
(r2 = 0.80–0.93).