Photolysis of nitrous acid in the presence of acetaldehyde

Abstract

The room temperature photolysis of dilute mixtures of HONO, NO, NO₂ and CH₃CHO in synthetic air at atmospheric pressure has been studied. Hydroxyl radicals are generated in this system from photodissociation of HONO. From measurements of the rates of formation of NO, NO₂, peroxyacetyl nitrate and methyl nitrate in a flow system using short photolysis times, kinetic information has been obtained for the reactions which occur following the attack of OH on acetaldehyde: OH + CH₃CHO = CH₃CO + H₂O. (4). The observations are consistent with the occurrence of a short chain reaction in which NO is oxidised to NO₂ by peroxy radical reactions of the type RO₂+ NO = RO + NO₂(R = CH₃CO, CH₃ or H). When R is CH₃CO, reaction with NO₂ to form peroxyacetylnitrate (PAN) competes with NO oxidation: CH₃CO₃+ NO = CH₃+ CO₂+ NO₂(6), CH₃CO₃+ NO₂= CH₃COO₂NO₂(PAN). (7), Kinetic analysis of the data gave k₆/k₇= 1.7 and k₄⩽ 2 × 10^–11 cm³ molecule^–1 s^–1 based on a previously determined value of k_{OH + HONO}= 6.6 × 10^–12 cm³ molecule^–1 s^–1.