State-of-the-art mass spectrometer reveals the complex chemical composition of downy birch emissions
Studying the emissions of VOCs from trees at the branch level is important to understand the conditions driving the variations of their chemical composition and amounts. Recent advances in mass spectrometry techniques have enabled the quantification of a larger number of compounds, such as hydrocarbons with up to 20 carbon atoms and oxygenated VOCs (OVOCs) with up to 4 oxygen atoms.
The Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus-PTR-ToF-MS) is such an instrument that can be used for monitoring emissions from a branch enclosure with high sensitivity and high time resolution. It was deployed at the Hyytiälä boreal forest research station (SMEAR II) in August 2019 to observe in real-time the emissions from a downy birch branch placed in an enclosure.
Scientists found that up to 90% of the emissions consisted of OVOCs. In particular, high emissions of C₈H₈O₃ (~60% of total) were noteworthy and possibly indicated that the tree suffered from abiotic stress.
While the results are limited to a specific time, location, and circumstances, they highlight the varying quantity and quality of emissions from downy birch, that are currently not represented with high accuracy in global models. In particular OVOCs directly emitted from trees are not considered, while they might contribute to the formation and growth of particulate matter. Additional measurements of this type allowing for a more detailed parametrization of emissions are needed.
Thomas S.J., Li H., Praplan A.P., Hellén H. and Bianchi F. (2022) Complexity of downy birch emissions revealed by Vocus proton transfer reaction time-of-flight mass spectrometer. Front. For. Glob. Change 5:1030348. doi:10.3389/ffgc.2022.1030348.