UC Davis

Trace analysis of volatile organic compounds (VOCs) during wildfires is imperative for environmental and health risk assessment. Because air is a heterogeneous system composed of gases, liquids, and solid particles that are continuously evolving in time and space, sampling is essential for assessing combustion related chemicals in air. The use of gas sampling devices mounted on unmanned aerial vehicles (UAVs) to chemically sample air during wildfires is of great interest because these devices can move freely about their environment, allowing for more representative air samples and the ability to sample areas dangerous or unreachable by humans. This work presents chemical data from air samples obtained in Davis, CA during the deadliest and most destructive wildfire in California’s history - the 2018 Camp Fire. The air sampling mechanism was an in-house manufactured micro-gas preconcentrator (µPC) embedded onto a compact battery-operated sampler that was returned to the laboratory for chemical analysis. Compounds commonly observed in wildfires were detected using gas chromatography mass spectrometry (GC-MS), including BTEX (benzene, toluene, ethylbenzene, m+p-xylene, and o-xylene), benzaldehyde, 1,4-dichlorobenzene, naphthalene, 1,2,3-trimethylbenzene and 1-ethyl-3-methylbenzene. Concentrations of BTEX were calculated and we observed that concentrations of benzene and toluene were highest with average concentrations of 4.7 and 15.1 µg/m3, respectively. Total BTEX values ranged from 4 to 48.5 µg/m3 with an average value of 20.2 µg/m3. A moderate negative correlation between daily AQI and toluene, benzene and toluene/benzene ratios. were observed as well. The viability of deploying this sampling technology in future wildfires was evaluated by fixing the µPC sampler to a UAV and sampling air while flying in the presence of a controlled experimental fire. Fuel contents of the experimental fire included various woods, carpet, electronics, and biomass. Numerous fire-related compounds including BTEX and aldehydes such as octanal and nonanal were detected upon fire ignition, even at a much smaller sampling time compared to air samples taken during the 2018 Camp Fire. Analysis of the air samples taken both stationary during the 2018 Camp Fire and mobile during an experimental fire show the successful operation of our sampler in a fire environment. Mobile VOC sampling technology has the potential to monitor important VOCs in localized areas during wildfires and provide additional information on the effects that wildfires have on the ambient environment.