Abstract
Abstract. Western US wildlands experience frequent and large-scale wildfires which are predicted to increase in the future. As a result, wildfire smoke emissions are expected to play an increasing role in atmospheric chemistry while negatively impacting regional air quality and human health. Understanding the impacts of smoke on the environment is informed by identifying and quantifying the chemical compounds that are emitted during wildfires and by providing empirical relationships that describe how the amount and composition of the emissions change based upon different fire conditions and fuels. This study examined particulate organic compounds emitted from burning common western US wildland fuels at the US Forest Service Fire Science Laboratory. Thousands of intermediate and semi-volatile organic compounds (I/SVOCs) were separated and quantified into fire-integrated emission factors (EFs) using a thermal desorption, two-dimensional gas chromatograph with online derivatization coupled to an electron ionization/vacuum ultraviolet high-resolution time-of-flight mass spectrometer (TD-GC × GC-EI/VUV-HRToFMS). Mass spectra, EFs as a function of modified combustion efficiency (MCE), fuel source, and other defining characteristics for the separated compounds are provided in the accompanying mass spectral library. Results show that EFs for total organic carbon (OC), chemical families of I/SVOCs, and most individual I/SVOCs span 2–5 orders of magnitude, with higher EFs at smoldering conditions (low MCE) than flaming. Logarithmic fits applied to the observations showed that log (EFs) for particulate organic compounds were inversely proportional to MCE. These measurements and relationships provide useful estimates of EFs for OC, elemental carbon (EC), organic chemical families, and individual I/SVOCs as a function of fire conditions.
Highlights
Wildfires in the western US have become larger and more frequent, and this trend is expected to continue in the coming decades (Dennison et al, 2014; Miller et al, 2009)
organic carbon (OC) and elemental carbon (EC) emission factors (EFs) were first related to the fire-integrated modified combustion efficiency (MCE)
MCE reflects the mix of combustion processes in the fire and is defined as background-corrected values of CO2/(CO2 + carbon monoxide (CO)) (Akagi et al, 2011; Ward and Radke, 1993)
Summary
Wildfires in the western US have become larger and more frequent, and this trend is expected to continue in the coming decades (Dennison et al, 2014; Miller et al, 2009). This is due to historical wildfire suppression, leading to high fuel loading and climate changes that include longer springs and summers, earlier snowmelts, and prolonged droughts (Dennison et al, 2014; Jolly et al, 2015; Spracklen et al, 2009; Westerling et al, 2006). Increased occurrences and magnitudes of wildfires will likely lead to greater smoke impacts on regional and global environments
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