What Can Charcoal Reflectance Tell Us About Energy Release in Wildfires and the Properties of Pyrogenic Carbon?

Abstract

Here, we explore how charcoal formation under different heating regimes and circumstances leads to chars of different physical properties. In order to do this, we have undertaken (1) carefully controlled laboratory experiments that replicate the different heating regimes that might be experienced during a wildfire and (2) two experimental wildfires where heat variations were monitored across the burn from which resulting charcoal has been studied. The charcoal properties were assessed using charcoal reflectance that measures the light reflected back from the charcoals structure and which links to changes in its structural properties. We find that increased total heat released during combustion positively correlates with increased charcoal reflectance and that this is evidenced from both our laboratory experiments and experimental wildfires. Charcoals that related to lower total heat release were found to have more lignin remaining than those subjected to greater heating indicating that charcoals formed in lower energy regimes are likely to be more susceptible to post-fire degradation. We conclude that charcoal reflectance may make a useful metric with which to determine the distribution of energy delivery across a burned area and that this may be utilized to inform both variations in fire severity and enable the prediction of long-term C budgeting for different types of wildfire.

Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics

“…(C) Unburned jack pine down wood (small dead branches) collected in 2012 from an unburned area in the same study region. (D) Unburned blocks cut from western red cedar (Thuja plicata) wood were included for comparison as a low-density wood used in a complementary study focusing specifically on charcoal reflectance (Belcher et al, 2018).…”

“…The significant correlations relationships of Ro% with T50 (r = 0.72) and C% (0.77; Table 3), as well as with other DSC parameters (Table S1), suggest that Ro may be a useful indicator of charcoal resistance to thermal degradation. This is important because it implies that PyC exhibiting higher Ro% will not only be more chemically inert in the post-fire environment (e.g., Ascough et al, 2010;Belcher et al, 2018), but also that such PyC will be more resistant to thermal degradation in subsequent fires. The potential of this additional metric for exploring charcoal recalcitrance, its resistance to thermal degradation in future wildfires, and more generally fire effects on C storage in wood and charcoal, is explored in more detail in Belcher et al (2018).…”

“…This is important because it implies that PyC exhibiting higher Ro% will not only be more chemically inert in the post-fire environment (e.g., Ascough et al, 2010;Belcher et al, 2018), but also that such PyC will be more resistant to thermal degradation in subsequent fires. The potential of this additional metric for exploring charcoal recalcitrance, its resistance to thermal degradation in future wildfires, and more generally fire effects on C storage in wood and charcoal, is explored in more detail in Belcher et al (2018). The results also highlight that the DSC analysis methods used here provide a relatively rapid and economic approach for the assessment of the resistance of PyC to removal from subsequent fires.…”

Dynamic of the structural alteration of biochar in ancient Anthrosol over a long timescale by Raman spectroscopy

“…Thus, with the exception of the more recent archaeological layers, it is impossible to use plant materials to produce these charcoals, which resemble the materials used by prehistoric populations. Because these charcoals are only included to provide a gradient of samples with distinct structural organizations, which is strongly influenced by the pyrolysis temperature [3,8,36,44], any plant material could be used.…”

“…The pyrolysis process promotes the loss of hydrogen and oxygen and the formation of long molecules of carbons, and as a consequence, the carbon structures evolve into graphite structures ( Fig 4A) [44]. Hemicellulose is decomposed at temperatures of approximately 202-315 C, while cellulose decomposes between 280 and 400˚C.…”