UV absorption cross sections (sigma(lambda)) for 3-methylbutanal, trans-2-methyl-2-butenal, and 3-methyl-2-butenal have been determined between 255 and 390 nm and as a function of temperature (273-305 K). A D-2 lamp and a 0.5 m spectrograph coupled to a charged-couple device were employed in these measurements. sigma(lambda) values were found to be independent of temperature in the range studied. The cross section data reported in this Letter were used to provide estimates of the photolysis rate coefficients (J(i)) for these compounds as a function of altitude in the troposphere. Photolysis and OH reaction both appear to be important in determining the atmospheric fate of these compounds. (c) 2008 Published by Elsevier B. V.