Abstract
Isoprene is emitted from the biosphere into the atmosphere, and may strengthen the defense mechanisms of plants against oxidative and thermal stress. Once in the atmosphere, isoprene is rapidly oxidized, either to isoprene-hydroxy-hydroperoxides (ISOPOOH) at low levels of nitrogen oxides, or to methyl vinyl ketone (MVK) and methacrolein at high levels. Here we combine uptake rates and deposition velocities that we obtained in laboratory experiments with observations in natural forests to show that 1,2-ISOPOOH deposits rapidly into poplar leaves. There, it is converted first to cytotoxic MVK and then most probably through alkenal/one oxidoreductase (AOR) to less toxic methyl ethyl ketone (MEK). This detoxification process is potentially significant globally because AOR enzymes are ubiquitous in terrestrial plants. Our simulations with a global chemistry-transport model suggest that around 6.5 Tg yr−1 of MEK are re-emitted to the atmosphere. This is the single largest MEK source presently known, and recycles 1.5% of the original isoprene flux. Eddy covariance flux measurements of isoprene and MEK over different forest ecosystems confirm that MEK emissions can reach 1–2% those of isoprene. We suggest that detoxification processes in plants are one of the most important sources of oxidized volatile organic compounds in the atmosphere.
| Original language | English (US) |
|---|---|
| Article number | 44 |
| Journal | Communications Earth and Environment |
| Volume | 1 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 2020 |
Bibliographical note
Funding Information:The authors would like to thank Bernhard Mentler (UIBK) for developing the ISOPOOH and IEPOX measurement protocol using different reagent ions, Ulrich Junghans (Helmholtz) for growing the sample plants, Frank Keutsch & Jean Rivera-Rios (Harvard University) for providing the 1,2-ISOPOOH standard and Holger Kopacka (UIBK) for the NMR analysis of the samples. We thank Xin Chen (UMN) for assistance with the model simulations, along with Steven Bertman (WMU) and the entire PROPHET-AMOS team for their support and contributions to the field campaign. We thank Martin Breitenlechner (UIBK) for contributions to the Hyytiälä field campaign. We thank the Institute of Microbiology from the University of Innsbruck for sharing the greenhouse facility. This study was supported by the Austrian Federal Ministry of Education, Science and Research within Sparkling Science (grant SPA 05/080—AiR and grant SPA 06/222—CHAMPIONS) and the University of Innsbruck. VOC flux measurements at Hyytiälä were supported by the European Commission under Horizon 2020 (H2020-INFRAIA-2014-2015, grant 654109, ACTRIS). VOC measurements during PROPHET were supported by the US National Science Foundation (NSF grants AGS‐1428257 and AGS‐1148951). GEOS‐Chem model development and simulations were supported by the US National Aeronautics and Space Administration (NASA grant NNX14AP89G). Computing resources at UMN were provided by MSI (www.msi.umn.edu).
Funding Information:
The authors would like to thank Bernhard Mentler (UIBK) for developing the ISOPOOH and IEPOX measurement protocol using different reagent ions, Ulrich Junghans (Helmholtz) for growing the sample plants, Frank Keutsch & Jean Rivera-Rios (Harvard University) for providing the 1,2-ISOPOOH standard and Holger Kopacka (UIBK) for the NMR analysis of the samples. We thank Xin Chen (UMN) for assistance with the model simulations, along with Steven Bertman (WMU) and the entire PROPHET-AMOS team for their support and contributions to the field campaign. We thank Martin Breitenlechner (UIBK) for contributions to the Hyytiälä field campaign. We thank the Institute of Microbiology from the University of Innsbruck for sharing the greenhouse facility. This study was supported by the Austrian Federal Ministry of Education, Science and Research within Sparkling Science (grant SPA 05/080—AiR and grant SPA 06/222—CHAMPIONS) and the University of Innsbruck. VOC flux measurements at Hyytiälä were supported by the European Commission under Horizon 2020 (H2020-INFRAIA-2014-2015, grant 654109, ACTRIS). VOC measurements during PROPHET were supported by the US National Science Foundation (NSF grants AGS‐1428257 and AGS‐1148951). GEOS‐Chem model development and simulations were supported by the US National Aeronautics and Space Administration (NASA grant NNX14AP89G). Computing resources at UMN were provided by MSI (www.msi.umn.edu).
Publisher Copyright:
© 2020, The Author(s).