Chemical characterization of biogenic SOA generated from plant emissions under baseline and stressed conditions: inter- and intra-species variability for six coniferous species

Abstract

Abstract. The largest global source of secondary organic aerosol in the atmosphere is derived from the oxidation of biogenic emissions. Plant stressors associated with a changing environment can alter both the quantity and composition of the compounds that are emitted. Alterations to the biogenic VOC profile could impact the characteristics of the SOA formed from those emissions. This study investigated the impacts of one global change stressor, increased herbivory, on the composition of SOA derived from real plant emissions. Herbivory was simulated via application of methyl jasmonate, a proxy compound. Experiments were repeated under pre- and post-treatment conditions for six different coniferous plant types. 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. Specifically, the following m/z were identified as a possible biogenic stress AMS marker with the corresponding HR ion(s) shown in parentheses: m/z 31 (CH3O+), m/z 58 (C2H2O2+, C3H6O+) m/z 29 (C2H5+), m/z 57 (C3H5O+), m/z 59 (C2H3O2+, C3H7O+), m/z 71 (C3H3O2+, C4H7O+), and m/z 83 (C5H7O+). 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.

Impacts of simulated herbivory on volatile organic compound emission profiles from coniferous plants

“…The short lived, slight emissions increase observed in these experiments could possibly be the result of an abiotic surface adsorption disruption effect; water displaces organic molecules previously adsorbed to the needle surfaces and produces a burst in measured emissions. This phenomenon has been observed in a natural forest environment where bursts of VOC emission were observed following rain (in a natural forest setting) or water application (in a laboratory setting) (Faiola et al, 2014a;Greenberg et al, 2012;Warneke et al, 1999). This would suggest that there was no significant stress treatment effect and that the small increase in some emissions observed on the treatment day could be a function of the treatment method itself rather than an actual stress response.…”

“…The objective of this paper is to present impacts of plant stress on the BVOC emission profile from the subset of experiments where continuous gas-phase measurements were available from the plant chamber. Analysis of the impacts of the stress treatment on the composition of subsequently formed SOA are presented in a separate paper (Faiola et al, 2014b).…”

“…This instrument was equipped with a custom-built pre-concentration system described previously by Faiola et al (2012Faiola et al ( , 2014a. The pre-concentration unit traps analytes on the Tenax © GR adsorbent and uses thermodesorption to inject compounds into the GC system.…”

“…The plant enclosure was continuously purged with zero air at 9.5 standard L min −1 (Aadco model 737 pure air generator). Gas-phase emissions from the saplings were continuously monitored with a gas chromatograph coupled to a mass spectrometer and flame ionization detector (Agilent model Faiola et al (2014b).…”

“…This study was a component of a project that investigated the effects of herbivory stress on the composition of biogenic SOA generated from BVOC emissions (Faiola et al, 2014b). Published data on this topic is extremely limited, so one goal of this work was to identify key tree species that could produce a large herbivore-treatment effect on SOA composition.…”