The heterogeneous reaction of di-2-ethylhexyl-phtalate, adsorbed on SiO2 aerosol, with OH radicals originating from a photosmog

The heterogeneous photodegradation of organic compounds adsorbed on various sands or on silica gel has been investigated previously in the bulk in static or rotating drum photoreactors. Since it is not possible to monitor or to control the active species of such degradation reactions we decided to construct a smog chamber optimized for long residence times of airborne aerosols. This facility enables us to monitor OH and O3 and other active species of the photosmog and to get insight into the mechanism of heterogeneous photodegradation of chemicals in the atmosphere. The decay of di(2-ethylhexyl)phthalate, adsorbed as a monolayer on SiO2 aerosol (Aerosil 200), is correlated with the concentration of OH in the smog chamber. The decay can be monitored down to the 1% level and it is observed to obey second order kinetics, proportional to OH and to the compound itself. The experiments yield a rate constant of 1.4.10E-11 cm3s-1 for this heterogeneous reaction of OH with di(2-ethylhexyl)phtha late. (ITA)