Assessing Volatile Organic Compound Exposures during FIREX-AQ and Beyond Using Experimental Diffusive Uptake Rates

Passive (diffusive) sampling using sorbents is an economical and versatile method of measuring pollutants in air, including volatile organic compounds (VOCs). Diffusive uptake rates (UTRs) are used to calculate the ambient concentrations of target VOCs over a set sample time duration. In this study, a simultaneous active/diffusive ambient air sampling technique on Tenax®TA was employed to measure 24-hr, 7, 14 and 28-day UTRs of several VOCs, including benzene, toluene, ethylbenzene, xylenes (BTEX), C6-C12 hydrocarbons, benzene derivatives, tetrachloroethylene, pinenes, limonene, other terpenes and alcohols. Samples were analyzed via thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) for desired analytes. Seven-day UTR values ranged from 0.17-0.59 mL/min and many compounds exhibited a linear relationship with UTR and time duration up to 14 days and a power fit relationship for rates up to 28 days. This may be the most comprehensive UTR tabulation of VOCs on Tenax®TA for time periods of 24 hours to 28 days available. The measured rates were applied to VOC data measured during the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign, a NASA/NOAA campaign with goals to determine the chemical composition of western US wildfire smoke and to assess human exposure to air toxics. Summer 2019 exposure levels of BTEX at five Northwestern cities were low and the cancer risk due to benzene was assessed during FIREX-AQ to be background or 1 x 10-6. In addition, The UTRs were also applied to subsequent fire seasons and will be compared to the 2019 results.