On the photolysis branching ratio of methyl ethyl ketone

Abstract

The methyl ethyl ketone (MEK) photolysis branching ratio (α) was re-evaluated by an end product analysis and box model simulations with the Master Chemical Mechanism (MCM). Using light emitting diodes centered at 285 nm or 315 nm, MEK was irradiated in the presence of nitric oxide and oxygen to produce peroxyacetic and peroxypropanoic nitric anhydride, CH3C(O)O2NO2 (PAN) and C2H5C(O)O2NO2 (PPN), which were quantified by gas chromatography. Box model simulations indicated that PPN is partially produced as a secondary product from chemistry initiated by reaction of the hydroxyl radical (OH) with MEK. Under NOx-limited experimental conditions or in the presence of ethane as an OH quencher, the product distribution observed required α = (7 ± 1)% + (1.1 ± 0.7) × 10−4 × (T-298) for 250K < T < 300K (2σ uncertainty), independent of pressure (at pressures > 266 hPa) and consistent with current IUPAC recommendations.