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.

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.

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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 seminal 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 individual species' context in terms of atmospheric chemistry.

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16In this study we capture and identify pyrolysis gases from prescribed burns conducted in pine 17 forests with a shrub understory using a manual extraction device. The device selectively sampled 18 emissions ahead of the flame front, minimizing collection of oxidized gases, with the captured 19 gases analyzed in the laboratory using infrared absorption spectroscopy. Results show that 20 emission ratios (ER) relative to CO for ethene, and acetylene were significantly greater than 21 previous fire studies, suggesting that the sample device was able to collect gases prior to ignition. 22Further evidence that ignition had not begun was corroborated by novel infrared detections of 23 several species, in particular naphthalene. With regards to oxygenated species, several aldehydes 24 (acrolein, furaldehyde, acetaldehyde, formaldehyde) and the carboxylic acids (formic, acetic) were 25 all observed; results show that ERs for acetaldehyde were noticeably greater while ERs for 26 formaldehyde and acetic acid were lower compared to other studies. The acetylene-to-furan ratio 27 also suggests that high temperature pyrolysis was the dominant process generating the collected 28 gases. This hypothesis is further supported by the presence of HCN and the absence of NH3. 29Atmos. Chem. Phys. Discuss., https://doi.levels of isoprene and 1,3-butadiene in the smoke from a living tree when compared to dead stumps 77 under the same conditions. Emission characteristics obtained during such campaigns can be 78 especially useful for the implementation or verification of effective burning techniques to 79 minimize the gases released during prescribed burns. 81However, few investigations have studied the pre-ignition or pyrolysis gases emitted prior to the 82 flaming combustion stage. Most prescribed burn studies have focused only on the flaming and 83 smoldering stages. The hotter flaming stage is characterized by more oxidized products and a 84 higher modified combustion efficiency (MCE) (Ward and Hao, 1991), which is defined as:The cooler smoldering phase with lower MCE values (typically ranging from 0.65-0.85) 86(Urbanski, 2013) displays more non-oxidized or less-oxidized species. The present study differs 87 from these earlier works in that we exclusively attempt to investigate pyrolysis, which is the first 88 step in the burning process (Collard et al., 2014), in particular we investigate the gas phase 89 pyrolysis species generated during prescribed burns. Primary mechanisms associated with 90 pyrolysis of biomass are char formation, depolymerization and species fragmentation. Volatile 91 products are generated and, if unstable, can continue to undergo secondary (non-combustion) 92 reactions such as cracking or recombination (Collard and Blin, 2014). Pyrolytic reactions produce 93 fuel gases that, if sufficient in quantity and in the presence of oxygen, will maintain the flame via 94 combustion pathways (Ward and Hardy, 1991; Di Blasi, 1993). Thus, the primary objectives of 95 the present study are a) to detect pyrolysis gases in pr...

The reflectance spectra of solid and liquids can be complicated since they depend not only on absorption, but also on the refraction, reflection, and scattering of light, all of which are wavelength dependent. The physical form and morphological effects associated with solid and liquid samples are thus known to affect their reflectance spectra in a non-linear fashion, particularly in the infrared. Measuring the optical constants n(ν) and k(ν) represents an alternative approach, allowing one to model these many effects and thus requiring fewer laboratory measurements. In this paper an overview is presented of the protocols used to measure the n/k optical constants, particularly for liquids. For the liquids, a multiple path length measurements approach is employed, and in this paper we demonstrate the method to determine the complex optical constants n(ν) and k(ν) of squalene. The resultant calculated spectra of 1 µm and 100 µm thick layers of squalene on an aluminum substrate as derived from the experimental n(ν) and k(ν) values are shown to demonstrate such effects. The public availability of the n(ν)/k(ν) data as well as solids hemispherical reflectance data are also discussed.