Abstract
Past studies suggest that certain properties of fire emitted particulate matter (PM) relate to the combustion phase (flaming, smoldering) of biomass burning, but to date there has been little consideration of such properties for use as combustion phase indicators. We studied the thermochemical properties of PM2.5 emitted from experimental and prescribed fires using multi-element scanning thermal analysis (MESTA). Resulting thermograms show that the carbon from PM2.5 generally can be grouped into three temperature categories: low (peak ~180 °C), medium (peak between 180–420 °C), and high (peak > 420 °C) temperature carbons. PM2.5 from smoldering phase combustion is composed of much more low-temperature carbon (fraction of total carbon = 0.342 ± 0.067, n = 9) than PM2.5 from the flaming phase (fraction of total carbon = 0.065 ± 0.018, n = 9). The fraction of low-temperature carbon of the PM2.5 correlates well with modified combustion efficiency (MCE; r2 = 0.76). Therefore, this MESTA thermogram method can potentially be used as a combustion phase indicator solely based on the property of PM2.5. Since the MESTA thermogram of PM2.5 can be determined independently of MCE, we have a second parameter to describe the combustion condition of a fire, which may refine our understanding of fire behavior and improve the accuracy of emission factor determinations. This PM2.5 indicator should be useful for discerning differential diffusion between PM2.5 and gases and providing insight into the impact of PM emission on atmospheric environment and the public health.
Highlights
Estimating gaseous and particulate emissions to the atmosphere from wildland fire remains a significant global challenge and high priority for air quality regulators, fire managers, and atmospheric scientists
Since the multi-element scanning thermal analysis (MESTA) thermogram of PM2.5 can be determined independently of modified combustion efficiency (MCE), we have a second parameter to describe the combustion condition of a fire, which may refine our understanding of fire behavior and improve the accuracy of emission factor determinations
We found that the low-temperature carbon peaks were relatively symmetrical and on average located at 180 ± 12.2 ◦ C
Summary
Estimating gaseous and particulate emissions to the atmosphere from wildland fire (wildfires and prescribed burns) remains a significant global challenge and high priority for air quality regulators, fire managers, and atmospheric scientists Many such emissions are strongly influenced by phase of combustion of biomass during fires, pyrolysis, flaming, smoldering, and glowing combustion, the combustion phase is typically more broadly categorized as flaming or smoldering [1]. Smoldering combustion, which dominates after flaming combustion has ceased, involves a combination of pyrolysis without flame and char oxidation through glowing combustion in a relatively oxygen-limited environment and is characterized by lower rates of heat release and less complete combustion of volatized gases and solids [4,5]. It is important to estimate the relative contribution of each phase in Atmosphere 2018, 9, 230; doi:10.3390/atmos9060230 www.mdpi.com/journal/atmosphere
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