Articles | Volume 15, issue 16
Research article
17 Aug 2015
Research article |  | 17 Aug 2015

Aqueous-phase oligomerization of methyl vinyl ketone through photooxidation – Part 2: Development of the chemical mechanism and atmospheric implications

B. Ervens, P. Renard, S. Tlili, S. Ravier, J.-L. Clément, and A. Monod

Abstract. Laboratory experiments of efficient oligomerization from methyl vinyl ketone (MVK) in the bulk aqueous phase were simulated in a box model. Kinetic data are applied (if known) or fitted to the observed MVK decay and oligomer mass increase. Upon model sensitivity studies, in which unconstrained rate constants were varied over several orders of magnitude, a set of reaction parameters was found that could reproduce laboratory data over a wide range of experimental conditions. This mechanism is the first that comprehensively describes such radical-initiated oligomer formation.

This mechanism was implemented into a multiphase box model that simulates secondary organic aerosol (SOA) formation from isoprene, as a precursor of MVK and methacrolein (MACR) in the aqueous and gas phases. While in laboratory experiments oxygen limitation might occur and lead to accelerated oligomer formation, such conditions are likely not met in the atmosphere. The comparison of predicted oligomer formation shows that MVK and MACR likely do negligibly contribute to total SOA as their solubilities are low and even reduced in aerosol water due to ionic strength effects (Setchenov coefficients). Significant contribution by oligomers to total SOA might only occur if a substantial fraction of particulate carbon acts as oligomer precursors and/or if oxygen solubility in aerosol water is strongly reduced due to salting-out effects.

Short summary
A detailed chemical mechanism is developed based on laboratory studies that predicts the formation of high molecular weight compounds in the aqueous phase of atmospheric aerosol particles. Model simulations using this mechanism for atmospheric conditions show that these pathways are likely not a substantial source of particle mass, unless unidentified precursors for these compounds exist that were not taken into account so far and/or the solubility of oxygen in aerosol water is overestimated.
Final-revised paper