A Closer Look at the Abundance of Oxygenated VOCs in the Colorado Front Range during Spring and Summer 2015

The Northern Front Range Metropolitan Area of Colorado regularly exceeds the National Ambient Air Quality Standards (NAAQS) for ozone. This region has a growing urban population and extensive oil and natural gas production in the nearby Denver-Julesberg Basin. In 2015, a large suite (40+ species) of volatile organic compounds (VOCs) were measured using a custom-built online multichannel gas chromatography system over 8 weeks in spring and 8 weeks in summer at the Boulder Atmospheric Observatory (BAO). We quantified three oxygenated VOCs (OVOCs): acetone, acetaldehyde, and methyl ethyl ketone (MEK). The summer data set was shortened to 5 weeks for the analysis presented here because aged wildfire smoke influenced the site during the last three weeks of the measurement campaign. Previous work found that the OVOCs accounted for almost a quarter of the total calculated OH reactivity yet the sources of these compounds were poorly reconstructed by a Positive Matrix Factorization (PMF) analysis. Here, we take a close look at the abundance of MEK to better understand the relationships between MEK and its known precursors as well as other OVOCs and secondary species. MEK can be directly emitted and it can be produced during the atmospheric oxidation of several different hydrocarbons (e.g. n-butane, 3-methyl hexane, i-pentane). We investigate dominant production pathways using a box model, and characterize local and synoptic meteorological conditions with respect to high and low MEK abundances.