Formation and Decomposition of Ozone by Ultraviolet Rays. III. The Influence of Dichlorodifluoromethane on the Formation and Decomposition of Ozone.

Abstract

The influence of dichlorodifluoromethane (freon 12) on the formation and decomposition of ozone by ultraviolet rays irradiated from a low pressure mercury vapor quartz lamp has been studied. The lamp used in this study was cylinder shaped 15 W and its main spectral lines were 184.9 nm and 253.7 nm. Freon gas was supplied to the annular middle space of a triple structure pipe that had the lamp in its center. Then, with ultraviolet rays irradiating from the lamp, the relationship between chlorine concentration and freon flow rate was examined. Likewise, air with a small amount of freon gas was supplied to the middle space. The intensity of ultraviolet rays (184.9 nm) after passing through the freon layer was also examined. In a further experiment, freon gas was supplied into the middle space and air with ozone whose concentration was kept constant (10 ppm) was supplied to the annular outside space of the pipe. Then, with ultraviolet rays irradiating from the lamp, the relationship between the decomposition ratio and the gas flow rate was examined. The following results were obtained : (1) Ozone is not decomposed by freon alone. (2) Freon is quite able to pass through 253.7 nm wavelength ultraviolet rays, but it hinders the formation of ozone by easily absorbing 184.9 nm wavelength ultraviolet rays. Ozone was not formed when air was mixed with freon gas of over 0.9 vol%. As the freon flow rate decreased, the formation rate of ozone gradually increased, up to 90% in the case of 0.025 vol%. (3) Freon absorbs 184.9 nm wavelength ultraviolet rays, and part of it forms chlorine after being decomposed. The highest chlorine concentrations recognized, in the case of a 0.11 l/min freon gas flow rate, was 900 ppm. The chlorine concentration produced was in proportion to the ratio of freon in the air. (4) After passing through the freon layer, 253.7 nm wavelength ultraviolet rays are able to decompose ozone without hindrance. That is to say, freon itself does not affect the decomposition of ozone by these ultraviolet rays.