Rate coefficients for the reaction of methylglyoxal (CH 3 COCHO) with OH and NO 3 and glyoxal (HCO) 2 with NO 3

Abstract. Rate coefficients, k , for the gas-phase reaction of CH 3 COCHO (methylglyoxal) with the OH and NO 3 radicals and (CHO) 2 (glyoxal) with the NO 3 radical are reported. Rate coefficients for the OH + CH 3 COCHO ( k 1 ) reaction were measured under pseudo-first-order conditions in OH as a function of temperature (211–373 K) and pressure (100–220 Torr, He and N 2 bath gases) using pulsed laser photolysis to produce OH radicals and laser induced fluorescence to measure its temporal profile. k 1 was found to be independent of the bath gas pressure with k 1 (295 K) = (1.29 ± 0.13) × 10 −11 cm 3 molecule −1 s −1 and a temperature dependence that is well represented by the Arrhenius expression k 1 ( T ) = (1.74 ± 0.20) × 10 −12 exp[(590 ± 40)/ T ] cm 3 molecule −1 s −1 where the uncertainties are 2σ and include estimated systematic errors. Rate coefficients for the NO 3 + (CHO) 2 ( k 3 ) and NO 3 + CH 3 COCHO ( k 4 ) reactions were measured using a relative rate technique to be k 3 (296 K) = (4.0 ± 1.0) × 10 −16 cm 3 molecule −1 s −1 and k 4 (296 K) = (5.1 ± 2.1) × 10 −16 cm 3 molecule −1 s −1 . k 3 ( T ) was also measured using an absolute rate coefficient method under pseudo-first-order conditions at 296 and 353 K to be (4.2 ± 0.8) × 10 −16 and (7.9 ± 3.6) × 10 −16 cm 3 molecule −1 s −1 , respectively, in agreement with the relative rate result obtained at room temperature. The atmospheric implications of the OH and NO 3 reaction rate coefficients measured in this work are discussed.