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Observations of sesquiterpenes and their oxidation products in central Amazonia during the wet and dry seasons
Citation:
Yee, L., G. Isaacman-VanWertz, R. Wernis, M. Meng, V. Rivera, N. Kreisberg, S. Hering, M. Bering, M. Glasius, M. Upshur, R. Thomson, F. Geiger, J. Offenberg, M. Lewandowski, I. Kourtchev, M. Kalberer, S. de Sa, S. Martin, M. Alexander, B. Palm, W. Hu, P. Campuzano-Jost, D. Day, J. Jimenez, Y. Liu, K. McKinney, P. Artaxo, J. Viegas, A. Manzi, M. Oliveira, R. de Souza, L. Machado, K. Longo, A. Goldstein, AND A. Gray Bé. Observations of sesquiterpenes and their oxidation products in central Amazonia during the wet and dry seasons. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, Germany, 18:10433-10457, (2018). https://doi.org/10.5194/acp-18-10433-2018
Impact/Purpose:
Emission of biogenic volatile organic compounds (BVOCs) from terrestrial vegetation represents the largest source of organic carbon to Earth's atmosphere. These emissions comprise a wide array of chemical species, including known isoprenoids: isoprene (C5), monoterpenes (C10), sesquiterpenes (C15), and diterpenes (C20). Isoprene, 1,3-dimethyl 10 butadiene (C5H8), is a hemi-terpene and the most highly emitted non-methane hydrocarbon to the atmosphere at levels ~500 TgC/year globally (Guenther et al., 2006, 2012). Global emissions of terpenes are estimated for monoterpenes (C10H16) at ~160 TgC/year, sesquiterpenes (C15H24) at ~30 Tg/year, and global emission estimates for diterpenes (C20H42) have yet to be made.
Description:
Biogenic volatile organic compounds (BVOCs) from the Amazon forest region represent the largest source of organic carbon emissions to the atmosphere globally. These BVOC emissions dominantly consist of volatile and intermediate-volatility terpenoid compounds that undergo chemical transformations in the atmosphere to form oxygenated condensable gases and secondary organic aerosol (SOA). We collected quartz filter samples with 12h time resolution and performed hourly in situ measurements with a semi-volatile thermal desorption aerosol gas chromatograph (SV-TAG) at a rural site (T3) located to the west of the urban center of Manaus, Brazil as part of the Green Ocean Amazon (GoAmazon2014/5) field campaign to measure intermediate-volatility and semi-volatile BVOCs and their oxidation products during the wet and dry seasons. We speciated and quantified 30 sesquiterpenes and 4 diterpenes with mean concentrations in the range 0.01–6.04ngm−3 (1–670ppqv). We estimate that sesquiterpenes contribute approximately 14 and 12% to the total reactive loss of O3 via reaction with isoprene or terpenes during the wet and dry seasons, respectively. This is reduced from ∼ 50–70% for within-canopy reactive O3 loss attributed to the ozonolysis of highly reactive sesquiterpenes (e.g., β-caryophyllene) that are reacted away before reaching our measurement site. We further identify a suite of their oxidation products in the gas and particle phases and explore their role in biogenic SOA formation in the central Amazon region. Synthesized authentic standards were also used to quantify gas- and particle-phase oxidation products derived from β-caryophyllene. Using tracer-based scaling methods for these products, we roughly estimate that sesquiterpene oxidation contributes at least 0.4–5% (median 1%) of total submicron OA mass. However, this is likely a low-end estimate, as evidence for additional unaccounted sesquiterpenes and their oxidation products clearly exists. By comparing our field data to laboratory-based sesquiterpene oxidation experiments we confirm that more than 40 additional observed compounds produced through sesquiterpene oxidation are present in Amazonian SOA, warranting further efforts towards more complete quantification.
URLs/Downloads:
DOI: Observations of sesquiterpenes and their oxidation products in central Amazonia during the wet and dry seasons
https://www.atmos-chem-phys.net/18/10433/2018/