The photooxidation of acetoin (AC; CH3C(O)CH(OH)CH3), a potential biobased C4 building block for the synthesis of renewable liquid hydrocarbon fuels, has been investigated under simulated tropospheric conditions at 318 K. AC was diluted in synthetic air and irradiated with UV light of 311 nm, a wavelength region part of the solar UV radiation available in the troposphere. Formic acid (HC(O)OH), acetic acid (CH3C(O)OH), formaldehyde (HCHO), methanol (CH3OH), and carbon dioxide (CO2) were identified as photooxidation products using FTIR spectroscopy as the detection method. Additionally, carbon monoxide (CO), acetaldehyde (CH3CHO) and biacetyl (CH3C(O)C(O)CH3) were also found to be produced as both photodissociation and photooxidation products. Yields of the photoproducts were quantified, which after 60 min of UV irradiation for the major photooxidation products, HC(O)OH, CH3C(O)OH, and CH3OH, are determined to be (10 ± 1) %, (12 ± 1) %, and (9 ± 1) %, respectively. The proposed reaction mechanism was validated using a reaction modeling study employing the KINSIM simulation platform. The close agreement between modeled and experimental data provides strong support for the validity of the proposed degradation pathways. These findings provide new insights into the atmospheric fate of AC and its role on secondary pollutant formation, while also contributing to the understanding of how biobased precursors might influence tropospheric chemistry. Carboxylic acids formed in the photooxidation of AC can be significant for atmospheric acidity and secondary organic aerosol (SOA) formation.
Saha et al. (Thu,) studied this question.