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.
Highlights
Every year, forest fires inject several hundred million metric tons of reactive organic compounds into the atmosphere globally [1,2,3]
In order to assess the stability of acetonitrile, acetone, isopentane, n-pentane, benzene, toluene furan, acrolein, methacrolein, 2-butanone, 2,3-butanedione, 2,5-dimethylfuran, and furfural in the thermal desorption (TD)
Based on the t-tests, it could be concluded with more than 95% confidence that there was no difference in the volatile organic compounds (VOCs) concentrations measured from the TD tube on day 0 and on each of the subsequent days for a period of up to 15 days for acetonitrile, isopentane, n-pentane, benzene, toluene, furan, and 2,5-dimethylfuran
Summary
Forest fires inject several hundred million metric tons of reactive organic compounds into the atmosphere globally [1,2,3]. Production of O3 from forest fires is highly variable [6], and each fire is unique in terms of emissions, transport pathway, plume injection heights, and photochemistry. Eulerian grid models often have difficulty accurately modeling downwind O3 concentrations [4,7,8,9]. Because of these complexities and the impacts at relatively low particulate matter concentrations, it is critical to develop additional tracers for forest fire influence. Several studies [10,11,12,13] have found acetonitrile to be an excellent tracer for biomass emission plumes in both laboratory and field studies and over a variety of ecosystems. Biomass burning is Atmosphere 2020, 11, 276; doi:10.3390/atmos11030276 www.mdpi.com/journal/atmosphere
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