Modeling the Global Budget of Methyl Ethyl Ketone

Methyl ethyl ketone (MEK) is one of the most abundant ketones in the atmosphere. MEK can be emitted directly into the atmosphere from both anthropogenic and natural sources, and it is also formed during the gas-phase oxidation of volatile organic compounds (VOCs). MEK is primarily lost due to photolysis, especially in the upper troposphere, and secondarily lost to reaction with OH. Similar to acetone, the photolysis of MEK may represent a source of HO_x (OH + HO₂) radicals in the upper troposphere. The degradation of MEK is also a source of acetaldehyde and formaldehyde, which in turn can also be a source of HO_x. Previous work suggests that the photolysis of MEK is somewhat uncertain and better values of the photolysis rate coefficients would help better constrain the loss of MEK and its role in the troposphere.

Here we improve the representation of MEK in the GEOS-Chem global chemical transport model (version 12, www.geos-chem.org). We have made several important changes to the model in order to improve our understanding of the atmospheric fate of MEK using the most up to date information available regarding the sources and sinks of MEK. First, we have implemented an improved scheme for the secondary production of MEK. Second, we include emissions of MEK from the biosphere using the MEGAN model. Third, we have performed a laboratory analysis of the temperature dependence of MEK photolysis cross-sections between 200-340 nm and incorporated the findings into our updated model. We use this model to investigate the global distribution, seasonality, sources, and lifetimes of MEK, as well as its importance to oxidation in the troposphere. Finally, we have made use of an assembled dataset of multiple aircraft campaigns to assess model skill.