Formation and Decomposition of Ozone by Ultraviolet Rays. II. The Influence of Temperature on the Formation and Decomposition of Ozone.

Abstract

The influence of temperature on the formation and decomposition of ozone by ultraviolet rays from a low pressure mercury vapor quartz lamp was studied. The main spectral lines for the lamp used in formation were 184.9 nm and 253.7 nm, and those used in decomposition were 253.7 nm. The lamps were cylinder shaped, and were 10 W. In the formation experiment, the temperature was changed from 55°C to 550°C (eleven levels), keeping the relative humidity constant. Ozone concentration initially increased, then decreased, as the gas flow rate decreased. During this process, the reversing zones at each temperature were recognized. The concentration decreased as the temperature rose, and the tendency was notable at higher temperatures. When the gas flow rate was low at 0.3 l/min or less, the ozone concentration was low, and it began to decrease greatly at about 200°C. It was extremely low at about 450°C. When the gas flow rate was high at 0.5 l/min or above, the ozone concentration was low, and remained constant up to about 200°C, thereafter decreasing greatly. It was extremely low at about 450°C. In the decomposition experiment, keeping the relative humidity constant, the reaction temperature was changed from 55°C to 275°C (eight levels). The differences between the heating decomposition ratio with and without irradiation by ultraviolet rays were measured. The heating decomposition reaction was recognized at around 100°C, and the decomposition ration rose as the gas flow rate decreased when the temperature was kept constant. The ratio also increased with increase in temperature under constant gas flow rate. It was about 70% at 250°C, 1.0 l/min. Data were obtained on temperature and decomposition ratios at various gas flow rates. The decomposition ratio difference increased as the temperature decreased when the rate of gas flow was unchanged, and also increased with decrease in the gas flow under constant temperature. Above a temperature of 250°C, the decomposition reaction of ozone was advanced mostly by heat. That is, the amount of irradiated ultraviolet rays was almost irrelevant.