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 kOH + HONO= 6.6 × 10–12 cm3 molecule–1 s–1.