EGU2020-9967
https://doi.org/10.5194/egusphere-egu2020-9967
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Atmospheric impact of sesquiterpenes in the Amazon rainforest

Nora Zannoni1, Stefan Wolff1, Anywhere Tsokankunku1, Matthias Soergel1, Marta Sa2, Alessandro Araujo3, and Jonathan Williams1
Nora Zannoni et al.
  • 1Max Planck Institute for Chemistry, Air Chemistry, Mainz, Germany (nora.zannoni@mpic.de)
  • 2Instituto Nacional de Pesquisas da Amazônia/ INPA – Manaus/AM, Brazil
  • 3Empresa Brasileira de Pesquisa Agropecuária (Embrapa) Belém/PA, Brazil

Sesquiterpenes (C15H24) are highly reactive biogenic volatile organic compounds playing an important role in atmospheric chemistry. Once emitted from the Earth’s surface, primarily by vegetation, they are rapidly oxidized to semivolatile oxygenated organic species that can lead to secondary organic aerosols (SOA) that influence climate. In the pristine Amazon rainforest environment oxidation of sesquiterpenes is initiated by OH and ozone.

We measured sesquiterpenes in March 2018 (wet season) and November 2018 (dry season) from central Amazonia, at the remote field site ATTO (Amazonian Tall Tower Observatory), Brazil. Samples were collected on adsorbent filled tubes equipped with ozone scrubbers at different heights above the forest canopy ; every three hours for two weeks at 80m and 150m (wet season) and every hour for three days at 80m, 150m and 320m (dry season). Samples were then analysed in the laboratory with a TD-GC-TOF-MS (Thermodesorption-Gas Chromatographer-Time Of Flight-Mass Spectrometer, Markes International). Simultaneous measurements of ozone and meteorological parameters were made at the nearby INSTANT tower. Identification of the chromatographic peaks was achieved by injection of standard molecules and by matching literature mass spectra. Quantification of the chemical compounds was achieved by injection of a standard mixture containing terpenes.The most abundant sesquiterpene measured at ATTO is (-)-α-copaene. Its diel profile varies with photosynthetically active radiation (PAR) and temperature, suggesting the canopy to be the main emission source. Interestingly, other identified sesquiterpenes show a consistent mirrored cycle, with their concentration being higher by night than by day. These varied mostly with RH suggesting the soil to be the main source of the emissions. Air samples taken at the ground are qualitatively and quantitatively different to those collected at different altitudes from the tower. Sesquiterpenes show a common maximum at sunrise (5 :00-7 :00 local time, UTC-4h) coincident with a strong decrease in ozone concentration (>50% decrease on average during the dry season). The strongest effect is registered during the dry season, when sesquiterpenes and ozone concentrations are highest and ozone loss is largest. The atmospheric impact of the measured sesquiterpenes will be discussed including ozone reactivity contributions and OH generation.

How to cite: Zannoni, N., Wolff, S., Tsokankunku, A., Soergel, M., Sa, M., Araujo, A., and Williams, J.: Atmospheric impact of sesquiterpenes in the Amazon rainforest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9967, https://doi.org/10.5194/egusphere-egu2020-9967, 2020

Display materials

Display file

Comments on the display material

AC: Author Comment | CC: Community Comment | Report abuse

Display material version 1 – uploaded on 07 May 2020
  • CC1: Comment on EGU2020-9967, Jürgen Kesselmeier, 08 May 2020

    Dear Nora and Co-workers,

    the course of sesquiterpenes in the air may point to a chemical destruction of these compounds by inceasing turbulent transport of oxidants from above the canopy starting with sunrise and decreasing into the night. May be there is only one dominant source at the ground? Soils?

    Jürgen

    Jürgen Kesselmeier, Max Planck Institute for Chemistry, Mainz, Germany

    • AC1: Reply to CC1, Jonathan Williams, 08 May 2020

      Yes agreed, both soil and canopy emissions of sesquiterpenes play a role (see box 4.3). The concentrations changes with time are the net result of the interplay between emissions, reaction with the oxidants above and the mixed layer turbulence.

  • AC2: Comment on EGU2020-9967, Nora Zannoni, 08 May 2020

    Indeed from our results it seems that both canopy and soil are sources of these compounds. The most concentrated compound, alpha-copaene is reported for being specifically emitted by Copaiba trees, a common tree species from which the copaiba oil is extracted. At the same time its lifetime to OH and ozone is ~a few hours, contrary to some sesquiterpenes whose lifetime is much shorter. I think within canopy measurements would be helpful to see which source has a stronger impact (more reactive compounds).

    • CC2: Reply to AC2, Jürgen Kesselmeier, 08 May 2020

      May be this can only be analysed using enclosures flushed with oxidant free air in  order to see a real primary emission.  Would be an interesting study.

      Jürgen