Measurements of atmospheric C₁₀–C₁₅ biogenic volatile organic compounds (BVOCs) with sorbent tubes

Abstract

Biogenic volatile organic compounds (BVOCs; e.g. terpenes) are highly reactive compounds typically present at sub-parts-per-billion mole fractions in the air. Due to this, their measurements are challenging and they may suffer losses during sampling, storage and analyses. Even though online measurements of BVOCs are becoming more common, the use of sorbent tubes is expected to continue because they offer greater spatial coverage compared to online measurements, and no infrastructure (e.g. electricity, housing/shelter with stable temperature and humidity, sampling lines) is required for sampling. In this study, the performance of an offline technique for the measurement of BVOCs based on sorbent tube sampling was evaluated. Tested compounds included eight monoterpenes, five sesquiterpenes and five oxygenated BVOCs, which are generally either directly emitted (1,8-cineol, linalool, bornyl acetate) or oxidation products (nopinone and 4-acetyl-1-methylcyclohexene). Two sorbent materials (Tenax TA and Carbopack B) and four tube materials (stainless steel (SS), SilcoNert 1000, glass and glass-coated SS) were used. The laboratory evaluations determined the storage stability, breakthrough volumes, suitable tube materials, recovery from ozone scrubbers and particulate filters, and sampling efficiency. In addition, an intercomparison between two laboratories was conducted. No multibed configurations were tested. Of the sorbent materials Tenax TA showed acceptable results for these BVOCs, while with Carbopack B losses and increases in some compounds were detected. Studied compounds were found to be stable in Tenax TA tubes for at least 1 month at −20 and at +20 ∘C. Breakthrough tests indicated that α- and β-pinene have clearly lower breakthrough volumes in the Tenax TA tubes used (4–7 and 8–26 L, respectively) than other terpenes (> 160 L). SS, SilcoNert 1000 and glass were all shown to be suitable tube materials. Results from Tenax TA sorbent tube sampling agreed with online sampling for most compounds. Heated SS tubes, sodium thiosulfate filters and KI/Cu traps were found to be suitable ozone scrubbers for the studied BVOCs. Tested particle filters had a greater impact on limonene (relative difference < +7 %) than on α- and β-pinene (relative difference ±2 %). The laboratory intercomparison of α- and β-pinene measurements showed that in general, measured values by the two laboratories were in good agreement with Tenax TA.