Photolysis Kinetics of Toluene, Ethylbenzene, and Xylenes at Ice Surfaces

Benzene, toluene, ethylbenzene, and xylenes (BTEX) are important organic pollutants. These compounds do not undergo direct photolysis in natural waters because their absorbance spectra do not overlap with solar radiation at the Earth's surface. Recent research has suggested that benzene is able to undergo direct photolysis when present at ice surfaces. However, the photolysis of toluene, ethylbenzene, and xylenes (TEX) at ice surfaces has not been investigated. Using fluorescence spectroscopy, photolysis rate constants were measured for TEX in water, in ice cubes, and in ice granules which reflect reactivity at ice surfaces. No photolysis was observed in water or ice cubes. Photolysis was observed in ice granules; rate constants were (4.5 ± 0.5) × 10^-4 s^-1 (toluene), (5.4 ± 0.3) × 10^-4 s^-1 (ethylbenzene), and (3.8 ± 1.2) × 10^-4 s^-1 (xylenes). Photolysis of TEX molecules appears to be enabled by a red shift in the absorbance spectra at ice surfaces, although photosensitization may also occur. The results suggest that direct photolysis could be an important removal pathway for TEX in snow-covered environments.