Identification of gas-phase pyrolysis products in a prescribed fire: first detections using infrared spectroscopy for naphthalene, methyl nitrite, allene, acrolein and acetaldehyde

Abstract

Abstract. Volatile organic compounds (VOCs) are emitted from many sources, including wildland fire. VOCs have received heightened emphasis due to such gases' influential role in the atmosphere, as well as possible health effects. We have used extractive infrared (IR) spectroscopy on recent prescribed burns in longleaf pine stands and herein report the first detection of five compounds using this technique. The newly reported IR detections include naphthalene, methyl nitrite, allene, acrolein and acetaldehyde. We discuss the approaches used for detection, particularly the software methods needed to fit the analyte and multiple (interfering) spectral components within the selected spectral micro-window(s). We also discuss the method's detection limits and related parameters such as spectral resolution.

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

“…The lightweight HCs detected by the FTIR include methane, ethane, ethene, acetylene, propene, allene, 1,3-butadiene, isoprene, and isobutene. Most have been previously identified in fire emissions using FTIR either in laboratory experiments (Burling et al, 2010;Christian et al, 2003Christian et al, , 2004Gilman et al, 2015;Goode et al, 1999;Hatch et al, 2017;Selimovic et al, 2018;Stockwell et al, 2014;Yokelson et al, 1996Yokelson et al, , 1997 or field settings (Akagi et al, 2013(Akagi et al, , 2014Alves et al, 2010;Burling et al, 2011;Goode et al, 2000;Hurst et al, 1994a, b;Karl et al, 2007;Paton-Walsh et al, 2010), but the present experiment reports the first IR detection of allene (Scharko et al, 2019). Figure 3 shows the individual correlations between these lightweight HCs and excess CO mixing ratios.…”

“…Naphthalene is a polycyclic aromatic hydrocarbon with several sources, including as a biomass burning emission product. It was detected using FTIR for the first time in these studies (Scharko et al, 2019). Its IR detection was not unexpected given that it has been observed in collected tar samples generated by the laboratory pyrolysis of similar fuel types (Safdari et al, 2018), but its identification in an experimental IR spectrum can be challenging as depicted in Fig.…”

“…Experimental details regarding FTIR measurement and ensuing spectral analysis procedures have been previously reported (Scharko et al, 2019) but are briefly summarized as follows: gases in the canisters were returned from the field to the laboratory and analyzed the same day or the following day using an 8 m White cell (Bruker A136/2-L) and FTIR; canisters were connected to the gas cell via 3/8 stainlesssteel tubing with both the tubing and gas cell heated to 70 • C to prevent analyte adhesion. The cell was coupled to a purged FTIR spectrometer (Bruker Tensor 37) equipped with a glow bar source, KBr beam splitter, and liquid-N 2 -cooled mercury cadmium telluride detector.…”

“…(Due to challenging experimental conditions and moderate CO band intensities, the OPAG detection limit was poor for these CO measurements and could not achieve 200 ppb.) Without an instrument to measure ambient CO with sufficient sensitivity we chose 200 ppb for an estimated background level, which is within the range for a typical CO mixing ratio (Seinfeld and Pandis, 2012). We note that the 200 ppb value is sufficiently small that it has a negligible effect on the calculated analyte / CO ratios.…”

“…5). Better retrievals for naphthalene were obtained using a higher spectral resolution (0.6 cm −1 ) since the Q branch of the ν 46 band is quite sharp (FWHM ∼ 1 cm −1 ), even at atmospheric pressure (Scharko et al, 2019) . Figure 6a plots the mixing ratios (ppm) for naphthalene as a function of excess CO (ppm), while Fig.…”