Uptake of Gaseous Hydrogen Peroxide by Submicrometer Titanium Dioxide Aerosol as a Function of Relative Humidity

Hydrogen peroxide (H2O2) is an important atmospheric oxidant that can serve as a sensitive indicator for HOx (OH + HO2) chemistry. We report the first direct experimental determination of the uptake coefficient for the heterogeneous reaction of gas-phase hydrogen peroxide (H2O2) with titanium dioxide TiO2, an important component of atmospheric mineral dust aerosol particles. The kinetics of H2O2 uptake on TiO2 surfaces were investigated using an entrained aerosol flow tube (AFT) coupled with a chemical ionization mass spectrometer (CIMS). Uptake coefficients (gamma H2O2) were measured as a function of relative humidity (RH) and ranged from 1.53 x 10(-3) at 15% RH to 5.04 x 10(-4) at 70% RH. The observed negative correlation of RH with gamma H2O2 suggests that gaseous water competes with gaseous H2O2 for adsorption sites on the TiO2 surface. These results imply that water vapor plays a major role in the heterogeneous loss of H2O2 to submicrometer TiO2 aerosol. The results are compared with related experimental observations and assessed in terms of their potential impact on atmospheric modeling studies of mineral dust and its effect on the heterogeneous chemistry in the atmosphere.