Articles | Volume 17, issue 6
Technical note
24 Mar 2017
Technical note |  | 24 Mar 2017

Technical note: Conversion of isoprene hydroxy hydroperoxides (ISOPOOHs) on metal environmental simulation chamber walls

Anne-Kathrin Bernhammer, Martin Breitenlechner, Frank N. Keutsch, and Armin Hansel

Abstract. Sources and sinks of isoprene oxidation products from low-NOx isoprene chemistry have been studied at the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber with a custom-built selective reagent ion time-of-flight mass spectrometer (SRI-ToF-MS), which allows quantitative measurement of isoprene hydroxy hydroperoxides (ISOPOOHs).

The measured concentrations of the main oxidation products were compared to chemical box model simulations based on the Leeds Master Chemical Mechanism (MCM) v3.3. The modeled ISOPOOH concentrations are a factor of 20 higher than the observed concentrations, and methyl vinyl ketone (MVK) and methacrolein (MACR) concentrations are up to a factor of 2 lower compared to observations, despite the artifact-free detection method.

Addition of catalytic conversion of 1,2-ISOPOOH and 4,3-ISOPOOH to methyl vinyl ketone (MVK) and methacrolein (MACR) on the stainless-steel surface of the chamber to the chemical mechanism resolves the discrepancy between model predictions and observation. This suggests that isoprene chemistry in a metal chamber under low-NOx conditions cannot be described by a pure gas phase model alone. Biases in the measurement of ISOPOOH, MVK, and MACR can be caused not only intra-instrumentally but also by the general experimental setup.

The work described here extends the role of heterogeneous reactions affecting gas phase composition and properties from instrumental surfaces, described previously, to general experimental setups. The role of such conversion reactions on real environmental surfaces is yet to be explored.

Short summary
Isoprene is the predominant non-methane compound emitted by the biosphere. In the atmosphere oxidation by OH under low NOx produces isoprene hydroxy hydroperoxides (ISOPOOHs). This work has found an effective conversion of ISOPOOHs to volatile carbonyls on metal environmental simulation chamber walls. Likely catalyzed decomposition reactions also occur for other hydroxyl hydroperoxides on metal surfaces.
Final-revised paper