Thermochemical Properties of PM2.5 as Indicator of Combustion Phase of Fires

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 similar to 180 degrees C), medium (peak between 180-420 degrees C), and high (peak > 420 degrees 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; r(2) = 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.