Optimization of a Method for the Detection of Biomass-Burning Relevant VOCs in Urban Areas Using Thermal Desorption Gas Chromatography Mass Spectrometry

Abstract

Forest fire smoke influence in urban areas is relatively easy to detect at high concentrations but more challenging to detect at low concentrations. In this study, we present a simplified method that can reliably quantify smoke tracers in an urban environment at relatively low cost and complexity. For this purpose, we used dual-bed thermal desorption tubes with an auto-sampler to collect continuous samples of volatile organic compounds (VOCs). We present the validation and evaluation of this approach using thermal desorption gas chromatography mass spectrometry (TD-GC-MS) to detect VOCs at ppt to ppb concentrations. To evaluate the method, we tested stability during storage, interferences (e.g., water and O3), and reproducibility for reactive and short-lived VOCs such as acetonitrile (a specific chemical tracer for biomass burning), acetone, n-pentane, isopentane, benzene, toluene, furan, acrolein, 2-butanone, 2,3-butanedione, methacrolein, 2,5- dimethylfuran, and furfural. The results demonstrate that these VOCs can be quantified reproducibly with a total uncertainty of ≤30% between the collection and analysis, and with storage times of up to 15 days. Calibration experiments performed over a dynamic range of 10–150 ng loaded on to each thermal desorption tube at different relative humidity showed excellent linearity (r2 ≥ 0.90). We utilized this method during the summer 2019 National Oceanic and Atmospheric Administration (NOAA) Fire Influence on Regional to Global Environments Experiment–Air Quality (FIREX-AQ) intensive experiment at the Boise ground site. The results of this field study demonstrate the method’s applicability for ambient VOC speciation to identify forest fire smoke in urban areas.

Mobile Near-Field Measurements of Biomass Burning Volatile Organic Compounds: Emission Ratios and Factor Analysis

“…As shown in Figure , the dominant species associated with factor 2 and factor 1 differ from each other and these species are dominated by the types of species expected from low- and high-temperature pyrolysis, respectively. Moreover, as shown in Figure C, the profile ratios between factor 2 and factor 1 (excluding small signals that contribute <0.1% of the total signal) show similar patterns when compared to the profile ratios between the low- and high-temperature profiles resolved by Sekimoto et al Signals that are enhanced in the low-temperature factors for both sets of spectra include m / z 139.08 (4-methyl guaiacol) and m / z 117.06 (5-hydroxymethyl tetrahydro 2-furanone or 5-hydroxymethyl tetrahydro 2-furfural) . Both guaiacol and furan derivatives are expected to be produced from the depolymerization of lignin and cellulose, which can explain their dominance in the low-temperature emission profile.…”

“…Moreover, as shown in Figure 3C, the profile ratios between factor 2 and factor 1 (excluding small signals that contribute <0.1% of the total signal) show similar patterns when compared to the profile ratios between the low-and high-temperature profiles resolved by Sekimoto et al Signals that are enhanced in the low-temperature factors for both sets of spectra include m/z 139.08 (4-methyl guaiacol) and m/z 117.06 (5-hydroxymethyl tetrahydro 2-furanone or 5-hydroxymethyl tetrahydro 2-furfural). 18 Both guaiacol and furan derivatives are expected to be produced from the depolymerization of lignin and cellulose, which can explain their dominance in the low-temperature emission profile. On the basis of these observations, we associate factor 2 with "lowtemperature" pyrolysis and factor 1 with "high-temperature" pyrolysis.…”

“…In 2018 and 2019, the focus of FIREX shifted to opportunistic sampling of real wildfires and agricultural burns. Gas-phase measurements using online mass spectrometers and offline cannisters were collected from stationary sites and on aircraft. Although scientific aircraft can sample many lofted biomass burning plumes over large distances, they cannot perform measurements of dynamic near-field emissions close to sources (fewer than hundreds of meters).…”

“…16 In 2018 and 2019, the focus of FIREX shifted to opportunistic sampling of real wildfires and agricultural burns. Gas-phase measurements using online mass spectrometers 17 and offline cannisters 18 close to sources (fewer than hundreds of meters). Given that the data from the Missoula FSL and other laboratory studies were typically collected <100 m from the burning fuel, 14,19 fresh near-field emissions data from real wildfires are necessary for drawing comparisons between real and simulated burns.…”

Health Risk Implications of Volatile Organic Compounds in Wildfire Smoke During the 2019 FIREX‐AQ Campaign and Beyond

“…Passive samples (7‐day averaging) taken at stationary sites served as background concentrations for compounds investigated for health risk (Miller et al., 2022 ). These diffusive samples collected ambient air for one week to one month during time periods of minimal to no wildfire influence in the following areas: McCall, Moscow, Lewiston, and Boise, ID, as well as Spokane, WA and Missoula, MT (Chandra et al., 2020 ; Miller et al., 2022 ; NASA, 2020 ). More in‐depth details on this background data set can be found in Miller et al.…”