PHOTOCHEMISTRY OF ACETONE UNDER TROPOSPHERIC CONDITIONS

The absorption cross sections of acetone were measured between 215 and 350 nm over the temperature range of 235 to 298 K using a diode array spectrometer. The quantum yield for the photodissociation of acetone was measured as a function of pressure at nine discrete wavelengths be tween 248 and 337 mn. At wavelengths longer than 270 nm, the quantum y ields were found to decrease with increasing pressure in accordance wi th the Stern-Volmer mechanism. The zero pressure quantum yield was fou nd to increase as the wavelength decreased and reached a value of unit y near 290 nm. The quantum yields at 308 nm were found to be nearly in dependent of temperature between 298 and 195 K. These results were use d to calculate an expression for the variation of the acetone photodis sociation quantum yield with pressure and wavelength. The calculated a tmospheric photolysis lifetime of acetone shows the photolysis to be t he main loss process for acetone in the upper troposphere, while react ion with the OH radicals dominates its loss rate near the Earth's surf ace. (C) 1998 Elsevier Science B.V. All rights reserved.