Chemical characterization of sesquiterpene emissions and oxidation in the Amazon using SV-TAG
Abstract
Biogenic volatile organic compounds (BVOCs) from the Amazon forest represent the largest regional source of organic carbon emissions to the atmosphere. These BVOC emissions dominantly consist of volatile and semi-volatile terpenoid compounds that undergo chemical transformations in the atmosphere to form oxygenated condensable gases and secondary organic aerosol (SOA). We have deployed the Semi-Volatile Thermal desorption Aerosol Gas Chromatograph (SV-TAG) at the rural T3 site located west of the urban center of Manaus, Brazil as part of the Green Ocean Amazon (GoAmazon) 2014/5 field campaign to measure hourly concentrations of semi-volatile BVOCs and their oxidation products during the wet and dry seasons. Primary BVOC concentrations measured by the SV-TAG include sesquiterpenes and diterpenes, which have rarely been speciated with high time-resolution. Most sesquiterpenes are observed at levels of tens of pptv anti-correlated with ozone. We estimate from the observed sesquiterpene, monoterpene, and isoprene concentrations, that sesquiterpenes dominate the local BVOC reactivity with ozone. Many sesquiterpenes present in ambient air were found to overlap with the sesquiterpene composition in essential oils from the Copaiba tree (Copaifera officinalisJacq. L.), commonly known as the "diesel tree" in the Amazon. One notable difference is the prevalence of beta-caryophyllene in copaiba oil, though it is rarely observed in ambient air, consistent with rapid reaction with ozone. Through synthesizing authentic standards, we quantified both gas- and particle-phase products from beta-caryophyllene oxidation in the ambient air. We also compare the ambient observations with laboratory based sesquiterpene oxidation experiments to identify new tracers for ambient sesquiterpene oxidation. We estimate the contribution of sesquiterpene oxidation to SOA by combining SV-TAG measurements with those from an additional suite of VOC and particle measurements deployed in the Amazon.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A43M..04Y
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE