Investigations on the gas-phase photolysis and OH radical kinetics of methyl-2-nitrophenols

Abstract

Methyl-2-nitrophenols can be emitted directly to the atmosphere or can be formed in situ via the oxidation of aromatic hydrocarbons. Nitrophenols possess phytotoxic properties and recent studies indicate their photooxidation is effective in producing secondary organic aerosols. Therefore, investigations on the major photooxidation pathways of these compounds with respect to assessing their environmental impacts and effects on human health are highly relevant. Presented here are determinations of the rate coefficients for the reactions of OH radicals with four methyl-2-nitrophenol isomers using a relative kinetic technique. The experiments were performed in a 1080 l photoreactor at (760 ± 10) Torr total pressure of synthetic air at (296 ± 3) K. The following rate coefficients (in units of cm³ molecule⁻¹ s⁻¹) have been obtained: 3-methyl-2-nitrophenol, (3.69 ± 0.70) × 10⁻¹²; 4-methyl-2-nitrophenol, (3.59 ± 1.17) × 10⁻¹²; 5-methyl-2-nitrophenol, (6.72 ± 2.14) × 10⁻¹²; 6-methyl-2-nitrophenol, (2.70 ± 0.57) × 10⁻¹². Photolysis of the methyl-2-nitrophenols with the superactinic fluorescent lamps (320 < λ < 480 nm, λ_max = 360 nm) used in the experiments was observed. Photolysis frequencies measured for the methyl-2-nitrophenols in the photoreactor have been determined and scaled to atmospheric conditions. The results suggest that photolysis rather than the reaction with OH radicals will be the dominant gas phase atmospheric loss process for methyl-2-nitrophenols.