Uptake of NO₂ to Deliquesced Dihydroxybenzoate Aerosol Particles

Abstract

The uptake of nitrogen dioxide (NO2), a major trace gas in the atmosphere, to deliquesced particles containing the sodium salts of hydroquinone (1,4-dihydroxybenzene) or gentisic (2,5-dihydroxybenzoic) acid was investigated at 40% relative humidity and 23 degrees C in an aerosol flow tube. The experiments were performed using the short-lived radioactive tracer 13N and a denuder technique. The observed uptake coefficient for NO2 was up to approximately 6 x 10(-3) for the hydroquinone disodium salt aerosol, which exceeds previously reported data in the range 10(-4) to 10(-3). The measured time dependence of NO2 uptake was fitted using a kinetic model taking into account reactant consumption in the particle phase, and keeping the bulk accommodation coefficient, alpha(b), and the rate constants for the reaction of dissolved NO2 with the deprotonated forms of the mentioned phenolic compounds as variables. We obtained alpha(b) = 0.024(-0.003)(+0.018) as a best estimate. For gentisic acid, the second-order rate constant was k2 = (2.9 +/- 0.1) x 10(8) L mol(-1) s(-1) and is reported for the first time. The data are consistent with bulk reaction limited uptake, without indications for a surface component in the kinetics.