The kinetics of gas-phase elemental mercury (Hg-0) oxidation on titania particle surfaces in the presence of UV irradiation was established. Overall reaction orders with respect to the gas-phase mercury concentration (a) and the UV intensity (P) were found to be 1.4 +/- 0.1 and 0.35 +/- 0.05 for the differential bed reactor, whereas values of a and P were 1.1 +/- 0.1 and 0.39 for the aerosol flow reactor (AFR). While the values are similar, the AFR results are more representative of the practical sorbent process. In the low-temperature range (<80 degreesC), the overall rate of initial mercury uptake increased as the temperature increased, indicating that it was a reaction-controlled process. At higher temperatures (> 110 degreesC), an increase of the temperature resulted in a decrease of the overall reaction rate, indicating an adsorption-controlled process.