The emission and atmospheric oxidation of biogenic volatile organic compounds from Sitka spruce
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Date
2023
Authors
Furnell, Hayley
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University College Cork
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Abstract
Biogenic volatile organic compounds (BVOCs) emitted by plants undergo chemical reactions in the atmosphere resulting in the formation of oxidised products and secondary organic aerosols (SOA), which have a large impact on climate. In this work an on-line time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) was used in laboratory studies to identify the main BVOCs emitted from the main plantation tree species in Ireland, Picea Sitchensis (Sitka spruce). Experiments have also been conducted to assess the atmospheric oxidation pathways of the BVOCs emitted by Sitka spruce and their SOA formation potential.
The ToF-CIMS was used in combination with off-line gas chromatography-mass spectrometry to identify the BVOC emissions from three Sitka spruce trees maintained in a plant growth chamber under conditions relevant to the Irish climate.
Fifty-two of the seventy-four BVOCs emitted from Sitka spruce were oxygenated compounds, with piperitone (C10H16O), an oxygenated monoterpene, being the dominant emission. Other prevalent emissions included isoprene and five monoterpenes (myrcene, β-phellandrene, δ-limonene, α-pinene, and camphene). Temperature, light intensity and stress were all found to alter the emission profiles, with different BVOCs exhibiting different responses. At the current conditions of the Irish climate the annual BVOC flux for isoprene was found to exceed that for piperitone, although this is expected to change in a warming climate.
A series of simulation chamber experiments was performed to determine, for the first time, the kinetics, products and mechanisms for the gas-phase reaction of piperitone with the main atmospheric oxidant the hydroxyl radical (OH•). The rate coefficient was determined by the relative rate method and used to calculate an atmospheric lifetime of under 2 hours. Calculations based on structure activity relationships identified the reaction with OH• as the dominant loss pathway for piperitone and was used to identify its most reactive sites. The ToF-CIMS detected thirty-three gas-phase oxidation products, and formation mechanisms for seventeen of the products have been proposed. The results from these experiments provide new and useful information on the atmospheric fate of piperitone.
Oxidation experiments were also conducted with OH• on all the BVOCs emitted by a Sitka spruce tree, to identify oxidation products, reaction pathways and determine the SOA formation potential of whole Sitka spruce BVOC emissions. Eight gas-phase BVOCs were identified as key reactive emissions, and upon reaction with OH• led to the formation of twenty-five gas-phase products and ninety-nine particle-phase products. Eight of these products were identified as originating from the oxidation of piperitone, myrcene and isoprene across the gas-phase and particle-phase, with the majority of the remining products resulting from oligomerisation reactions. Rapid SOA formation was observed soon after the onset of oxidation, likely due to the formation of low volatility oxidation products which caused new particle formation. SOA yields were estimated to be around 15%.
Overall, this work has produced a wealth of new information on the emission and atmospheric oxidation of BVOCs emitted from Sitka spruce, which will be valuable to decision makers in the forestry sector. Moreover, the research highlights the importance of assessing BVOC emissions and the associated SOA formation potential prior to establishing tree plantations.
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Keywords
Sitka spruce (Picea Sitchensis) , Biogenic volatile organic compounds , Secondary orgnaic aerosols
Citation
Furnell, H. 2023. The emission and atmospheric oxidation of biogenic volatile organic compounds from Sitka spruce. PhD Thesis, University College Cork.