The global budget of Methyl Ethyl Ketone (MEK)

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 most abundant atmospheric ketone), the photolysis of MEK may represent a source of HO_x (OH + HO₂) radicals in the upper troposphere. In previous work, we have updated and examined the sources and sinks of MEK to the troposphere, including updated temperature dependence of MEK absorption cross-sections and a previously un-described oceanic source of MEK.

We have now fully implemented the results of this research in the GEOS-Chem global chemical transport model (version 12, www.geos-chem.org), with which we have created a global budget of MEK, which includes updated photolysis and chemistry, as well as all known major sources and sinks of the compound to the atmosphere. We have further evaluated our simulation by comparing model-derived MEK abundances with those measured from multiple aircraft campaigns, in particular the ATom global atmospheric tomography measurements. With this information, we can quantify the global annual distribution of MEK in the atmosphere. We further identify the seasonality, location, magnitude and relative importance of the various sources and sinks of MEK. Finally, we explore the relative importance of MEK in the tropospheric production of HO_x as compared to other non-ozone sources. In this way, we explore whether atmospheric chemistry simulations need to explicitly take MEK production and photolysis into account in order to properly represent atmospheric oxidative potential.