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

Abstract. 3,3-dimethylbutanal and 3,3-dimethylbutanone 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 3,3-dimethylbutanal and 3,3-dimethylbutanone with atmospheric oxidants (Cl atoms, OH and NO₃ radical). The kinetic experiments were performed at 710 ± 30 Torr and at room temperature (298 ± 5 K) using a relative method and FTIR (Fourier Transform Infrared Spectroscopy) to monitor the reactions. The rate coefficients (k in units of cm³ molecule^-1 s^-1) obtained were: k_{Cl+33DMbutanal} = (1.27 ± 0.08) × 10^-10, k_{Cl+33DMbutanone} = (4.22 ± 0.27) × 10^-11, and k_{OH+33DMbutanone} = (1.25 ± 0.05) × 10^-12. The reaction products were also determined using FTIR and GC-MS (Gas Chromatography/Mass Spectrometry). The main products observed were short carbonyl compounds, including acetone, formaldehyde and 2,2-dimethylpropanal. In the presence of NO, nitrated compounds are formed, and in large NO₂ concentrations peroxyacetyl nitrate (PAN) and peroxy-3,3-dimethylbutyryl nitrate were clearly 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, with a range of POCP_E of 15–69, and secondary organic aerosol formation, potentially worsening air quality and contributing to photochemical smog.