PHOTOOXIDATION OF EXHAUST POLLUTANTS .2. PHOTOOXIDATION OF CHLOROMETHANES - DEGRADATION EFFICIENCIES, QUANTUM YIELDS AND PRODUCTS

The photochemical decomposition and oxidation, of CH(x)Cl(y) (x = O-3, y = 4-x) was investigated in the gas phase by irradiation with a low pressure mercury lamp in an oxygen atmosphere. The degradation efficiency depends on the concentration of the pollutant, the power output of the UV-lamp and the irradiation time. The quantum yields for degradation at 185 nm were measured to be around 1 at low CH(x)Cl(y) concentration in the 10(-3) range. For CH2Cl2 and CHCl3 however, we observed a drastic increase of the quantum yields to values up to one hundred at high CH(x)Cl(y) concentration in the 10(-2) range. For CH3Cl and CCl4 no significant increase of quantum yield with concentration was found. In addition to the main products HCl, phosgene and formyl chloride we found CO, CO2 and formic acid. The mechanisms of their formation are discussed in detail.