Simon Schallhart

Pure biogenic new particle formation (NPF) induced by highly oxygenated organic molecules (HOMs) could be an important mechanism for pre-industrial aerosol formation. However, it has not been unambiguously confirmed in the ambient due to the scarcity of truly pristine continental locations in the present-day atmosphere or the lack of chemical characterization of NPF precursors. Here, we report ambient observations of pure biogenic HOM-driven NPF over a peatland in southern Finland. Meteorological decoupling processes formed an “air pocket” (i.e., a very shallow surface layer) at night and favored NPF initiated entirely by biogenic HOM from this peatland, whose atmospheric environment closely resembles that of the pre-industrial era. Our study sheds light on pre-industrial aerosol formation, which represents the baseline for estimating the impact of present and future aerosol on climate, as well as on future NPF, the features of which may revert toward pre-industrial–like conditions due to air pollution mitigation.

Biogenic Volatile Organic Compound (BVOCs; e.g. terpenes) are highly reactive compounds with very low amount fractions in the air. Due to this, their measurements are challenging and they may suffer losses during sampling, storage and analyses. In this study, the performance of an off-line technique for the measurement of BVOCs based on sorbent tubes sampling was evaluated. Even though online measurements of BVOCs are becoming more and more common, the use of sorbent tubes is expected to continue since they have greater spatial coverage compared to online GC measurements and no infrastructure is needed for sampling. Tested compounds included 8 monoterpenes, 5 sesquiterpenes and 5 oxy BVOCs, which are generally either directly emitted (1,8-cineol, linalool, bornylacetate) or oxidation products (nopinone and 4-methylacetylcyclohexene). 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 storage stability, breakthrough volumes, suitable tube materials, recoveries from ozone scrubbers and particulate filters and the sampling efficiency. In addition, an intercomparison between two laboratories was conducted. Of the sorbent materials Tenax TA showed acceptable results for these BVOCs, while with Carbopack B losses and increases of some compounds were detected. Studied compounds were found to be stable in Tenax TA tubes for at least one month at ±20 °C. Breakthrough tests indicated that α- and β-pinene have clearly lower breakthrough volumes in Tenax TA (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 studied BVOCs. Tested particle filters had a greater impact on limonene than on α- and β-pinene. 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.