Reactivity study of 3,3-dimethylbutanal and 3,3-dimethylbutanone: kinetics, reaction products, mechanisms, and atmospheric implications

Abstract

3,3-dimethylbutanal (33DMbutanal, (CH3)3CCH2C(O)H) and 3,3-dimethylbutanone (33DMbutanone, (CH3)3CC(O)CH3) are carbonyl compounds that could play a key role in tropospheric chemistry. To better understand the effects of carbonyl compounds in the atmosphere, a kinetic and mechanistic study was conducted on the degradation of 33DMbutanal and 33DMbutanone with atmospheric oxidants (Cl atoms, OH and NO3 radicals). The kinetic experiments were performed at 710 ± 30 Torr and at room temperature (298 ± 5 K) using a relative method and Fourier transform infrared (FTIR) spectroscopy to monitor the reactions. The rate coefficients (k in units of cm3 molec.−1 s−1) obtained were kCl+33DMbutanal = (1.27 ± 0.08) × 10−10, kCl+33DMbutanone = (4.22 ± 0.27) × 10−11, and kOH+33DMbutanone = (1.26 ± 0.05) × 10−12. The reaction products were also determined using FTIR spectroscopy and gas chromatography–mass spectrometry (GC-MS). The main products observed were carbonyl compounds, including acetone, formaldehyde, and 2,2-dimethylpropanal. In the presence of NO, nitrated compounds were also formed, and, at high NO2 concentrations, peroxyacetyl nitrate (PAN) and peroxy-3,3-dimethylbutyryl nitrate were identified. Other unquantified compounds were multifunctional organic compounds and organic acid of low volatility. Both 33DMbutanal and 33DMbutanone degrade rapidly near emission sources with minimal impact on radiative forcing. However, they may contribute to tropospheric ozone (O3), with a photochemical ozone creation potential (POCP) range of 15–69, and secondary organic aerosol (SOA) formation, potentially worsening air quality and contributing to photochemical smog.