Stress-Induced Changes to VOC Emissions from Coniferous Trees and their Impacts on SOA

 

Author

Tim VanReken — Washington State University

Category

Secondary Organic Aerosol

Description

Plant stressors associated with a changing environment can alter both the quantity and composition of the compounds that are emitted. This study investigated the effects of one global change stressor, increased herbivory, on plant emissions from several different coniferous species. Herbivory was simulated in the laboratory via exogenous application of methyl jasmonate, an herbivory proxy. Gas-phase species were measured continuously with a gas chromatograph coupled to a mass spectrometer and flame ionization detector (GC-MS-FID). Stress responses varied between the different plant types and even between experiments using the same set of saplings. The compounds most frequently impacted by the stress treatment were alpha-pinene, beta-pinene, 1,8-cineol, beta-myrcene, terpinolene, limonene, and the cymene isomers. Individual compounds within a single experiment often exhibited a different response to the treatment from one another. Alterations to the biogenic VOC profile also impacted the characteristics of the SOA formed from those emissions. VOCs emitted from the plants were oxidized to form SOA via dark ozone-initiated chemistry. The SOA particle size distribution and chemical composition were measured using a scanning mobility particle sizer (SMPS) and Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-AMS), respectively. The aerosol mass spectra of pre-treatment biogenic SOA from all plant types tended to be similar with correlations usually greater than or equal to 0.90. The presence of a stressor produced characteristic differences in the SOA mass spectra. Specific m/z were identified as possible biogenic stress markers. The first aerosol mass spectrum of SOA generated from the oxidation of the plant stress hormone, methyl jasmonate, is also presented. Elemental analysis results demonstrated an O:C range of baseline biogenic SOA between 0.3-0.47. The O:C of standard methyl jasmonate SOA was 0.52. Results presented here could be used to help identify a biogenic plant stress marker in ambient datasets collected in forest environments.