Gas-phase pyrolysis products emitted by prescribed fires in pine forests with a shrub understory in the southeastern United States

Abstract

Abstract. In this study we identify pyrolysis gases from prescribed burns conducted in pine forests with a shrub understory captured using a manual extraction device. The device selectively sampled emissions ahead of the flame front, minimizing the collection of oxidized gases, with the captured gases analyzed in the laboratory using infrared (IR) absorption spectroscopy. Results show that emission ratios (ERs) relative to CO for ethene and acetylene were significantly greater than in previous fire studies, suggesting that the sample device was able to collect gases predominantly generated prior to ignition. Further evidence that ignition had not begun was corroborated by novel IR detections of several species, in particular naphthalene. With regards to oxygenated species, several aldehydes (acrolein, furaldehyde, acetaldehyde, formaldehyde) and carboxylic acids (formic, acetic) were all observed; results show that ERs for acetaldehyde were noticeably greater, while ERs for formaldehyde and acetic acid were lower compared to other studies. The acetylene-to-furan ratio also suggests that high-temperature pyrolysis was the dominant process generating the collected gases.

In-situ measurement of pyrolysis and combustion gases from biomass burning using swept wavelength external cavity quantum cascade lasers

“…The steady decrease in MCE during the burn process is consistent with this mechanism, as the fraction of smoldering material upwind of the measurement path increases during the flame front propagation. The measured MCE in the post-flame region of ∼0.7 is also lower than the value ∼0.8 typically observed from smoldering in biomass burning studies [5,10,15]. In addition to the mechanism discussed above, the lower observed MCE may result from the in-situ measurement at close proximity to the smoldering fuel source which reduces the likelihood of reactive CO decreasing in concentration during propagation to a remote measurement or through sampling effects.…”

“…An increase in NH 3 is detected, which peaks later in time than H 2 O and CO 2 . This observation suggests that the NH 3 is emitted more strongly from smoldering sections, including the previously burned material upwind of the beam path [7,10]. Elevated levels of C 2 H 4 and MeOH are also detected as the flame front propagates through the beam path.…”

“…Detailed knowledge of the gas composition released from biomass burning, and its dependence on fuel source and burning conditions, is needed to improve models for plume chemistry and atmospheric transport [1,2]. Experiments to study biomass burning have included small-scale laboratory experiments [3,4], larger-scale laboratory burns [5], and prescribed outdoor burns [6][7][8][9][10]. These experiments have detected and identified dozens of trace gases emitted from biomass burning [1,2,[9][10][11][12].…”

“…Extractive methods are often used to sample gases downwind of a fire or close to the fuel source, typically followed by laboratory or on-site analysis with analytical instruments [9]. Extractive methods used for biomass burning analysis include proton transfer reaction mass spectrometry (PTR-MS) [12], gas chromatography mass-spectrometry (GC-MS) [11], and gas-phase Fouriertransform infrared spectroscopy (FTIR) [7][8][9][10]. Extractive techniques can be extremely sensitive, but even when sampling gases close to the fuel there is a possibility that species may react or adsorb to surfaces before reaching the measurement region, thereby changing the composition or concentrations of gases in the sample.…”

Dynamic infrared gas analysis from longleaf pine fuel beds burned in a wind tunnel: observation of phenol in pyrolysis and combustion phases

“…In most cases, a comparison of compounds found in the RFL laboratory burns and the Ft. Jackson 2018 field burns finds Ft. Jackson mixing ratios approximately 4 to 10 times greater than those of the RFL 2018 tunnel data. Field-scale measurements typically yield more emissions than experiments conducted in the laboratory due to larger fuel quantities (Yokelson et al, 2013;Scharko et al, 2019b;Weise et al, 2015). However, while the mixing ratios may differ, the information describing the composition of the mixture is relative in nature and is contained in the log ratios of the various gases.…”