Quantum yields of the direct Phototransformation of 1,2,4,7,8‐penta‐ and 1,2,3,4,7,8‐hexachlorodibenzofuran in aqueous Acetonitrile and their sunlight half‐lives∗

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Abstract
Photochemistry of two polychlorodibenzofurans (PCDFs), 1,2,4,7,8‐pentachlorodibenzofuran (1,2,4,7,8‐P5CDF) (1) (3.870 × 10‐6M) and 1,2,3,4,7,8‐H6CDF (2) (1.272 × 10‐6M) dissolved in water‐acetonitrile (1:1 v/v) was investigated using wavelengths near 313nm. The quantum yields for the direct phototransformation of P5CDF 1 and H6CDF 2 were found to be (1.295±0.087) x 10‐2 and (6.964±0.234) × 10‐4, respectively. The quantum yields and absorption spectral data for PCDFs 1 and 2 together with solar intensity data from the literature were used to determine the direct sunlight (environmental) photolytic transformation first‐order rate constants of these pollutants present in aquatic systems under conditions of varying sunlight during spring, summer, fall, and winter season. For instance, in summer, the calculated midday, midseason sunlight photolysis first‐order rate constants for furans 1 and 2 near the surface of water bodies at 40° north latitude were 3.082 ±0.207 and (11.630 ± 0.391)× 10‐2h‐1, respectively; whereas the values of the corresponding sunlight half‐lives were 0.226±0.015 and 5.97±0.20h.