UV absorption cross-sections for CCl3CHO, CCl2FCHO and CCIF2CHO have been determined over the wavelength range 200-370 nm and at temperatures in the range 298-243 K using a dual beam diode array spectrometer. The spectra show characteristic absorption due to the n --> pi* transition of the C=O group with absorption maxima around 300 nm. On substitution of Cl by F in the CX3 group the absorption maxima showed a shift to longer wavelengths and a corresponding increase in the intensity of the absorption in the region of atmospheric photolysis. With decreasing temperature, all three aldehydes showed a small non-negligible decrease in the cross-section in the long wavelength tail of the absorption band, and an increase in the cross-section around the absorption maxima. A two-dimensional photochemical model has been used to calculate atmospheric lifetimes due to photodissociation and OH radical loss. (C) 1998 Elsevier Science S.A.