Atmospheric Behaviour of Chloroacetaldehydes

Chloroacetaldehydes are intermediates in the atmospheric degradation of several important chlorinated alkanes and alkenes. The most probable loss processes which determine their atmospheric lifetimes are photolysis and reactions with OH radicals and CI atoms. In the present work, UV absorption spectra between 235 and 345 nm and the rate constants for the reactions with OH and CI have been determined at room temperature for CCI3CHO, CHCl2CHO, andCH2ClCHO. The experiments were performed in large reaction chambers from Duran glass (400-500 1 volume). UV absorption coefficients were measured using a built-in White mirror system (optical pathlengths ≤ 150 m) and a diode array spectrometer. Rate constants were determined by relative rate techniques with CH3ONO and Cl2 photolysis as stationary photolytic OH and CI sources, respectively. Reaction mixtures were analyzed by in-situ long-path IR absorption using an FTIR spectrometer and by gas chromatography. From the results it is suggested that the tropospheric degradation of chloroacetaldehydes proceeds by photolysis and reaction with OH, both being of comparable importance.