Phototransformation processes of 2,4-dinitrophenol, relevant to atmospheric water droplets.

This paper shows that the polychromatic quantum yield for the photolysis of 2,4-dinitrophenol (24DNP) in the wavelength interval of 300-500 nm is (8.1+/-0.4) x 10(-5) for the undissociated phenol, and (3.4+/-0.2) x 10(-5) for the phenolate. The second-order rate constants for reaction with ()OH were determined here as (1.76+/-0.05) x 10(9) M(-1) s(-1) and (2.33+/-0.11) x 10(9) M(-1) s(-1) for the phenol and the phenolate, respectively. By combining laboratory results and a simple modelling approach of the atmospheric aqueous phase, this work shows that the direct photolysis and the reaction with ()OH would play a comparable role in the degradation of 24DNP at pH>4. The ()OH reaction would prevail for pH<4. Both pathways would be more important than the night-time reaction with *NO(3) as removal processes for 24DNP in the atmospheric waters.