Theoretical study of the reaction mechanism and kinetics of low-molecular-weight atmospheric aldehydes (C1–C4) with NO2

Accurate description of atmospheric reactions of a series of low-molecular-weight (LMW) aldehydes (C1–C4) with NO2 has been modeled using a direct dynamic approach. The profiles of the potential energy surface were constructed at the BMC-CCSD//MPWB1K/6-311G(d,p) level of theory, and two different pathways have been found: H-abstraction and NO2-addition. The modeling results found that the contribution of NO2-addition reaction pathway to the total rate constant is very small and thus this kind of pathway is insignificant in atmospheric conditions. The predicted H-abstraction products are mainly reactive acyl radical and nitrous acid (HONO) which is very mutagenic and carcinogenic pollutant as well as the precursor of acid deposition. The rate constants of both pathways were also deduced by using canonical variational transition state theory incorporating with the small curvature tunneling correction within 200–360 and 360–2000 K. Theoretical overall rate constants are in good agreement with the available experimental values, whose increase in the order of kformaldehyde < kacetaldehyde < kpropanal < kbutanal, implying that relative long-chain LMW aldehydes are more reactive toward NO2 than those short-chain LMW aldehydes in the atmospheric condition. At 298 K, the total rate constants of LMW aldehydes (C1–C4) with NO2 are obtained as 1.65 × 10−25, 1.43 × 10−24, 3.39 × 10−24 and 1.83 × 10−23 cm3 molecule−1 s−1, respectively.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (167 K)Download as PowerPoint slideHighlights► Atmospheric reaction mechanism of aldehydes (C1–C4) with NO2. ► Major H-abstraction from and minor NO2-addition onto aldehydes (C1–C4). ► Atmospheric reaction kinetics of aldehydes (C1–C4) with NO2. ► Theoretical prediction model. ► Theoretical rate constants are in good agreement with available experimental values.