Kinetics and mechanisms of heterogeneous reaction of gaseous hydrogen peroxide on mineral oxide particles

Abstract

Recent studies have shown that heterogeneous reactions of hydrogen peroxide (H2O2) on aerosol surfaces may play an important role in tropospheric chemistry. The data concerning the kinetics and mechanisms of these reactions, however, are quite scarce so far. Here, we investigated, for the first time, the heterogeneous reactions of gaseous H2O2 on SiO2 and α-Al2O3 particles, two major components of mineral dust aerosol, using transmission-Fourier Transform Infrared (T-FTIR) spectroscopy, and high-performance liquid chromatography (HPLC). It is found that H2O2 molecularly adsorbs on SiO2, and a small amount of molecularly adsorbed H2O 2 decomposes due to its thermal instability. For α-Al 2O3, catalytic decomposition of H2O2 evidently occurs, but there is also a small amount of H2O 2 molecularly adsorbed on the particle surface. The BET uptake coefficients of H2O2 on both particles appear to be independent of gaseous H2O2 concentration (1.27-13.8 ppmv) and particle sample mass (2.8-6.5 mg for SiO2 and 8.6-18.9 mg for α-Al2O3), but are strongly dependent on relative humidity with the values ranging from (1.55 ± 0.14) × 10 -8 and (1.21 ± 0.04) × 10-7 at 2% RH to (0.61 ± 0.06) × 10-8 and (0.76 ± 0.09) × 10 -7 at 76% RH for SiO2 and α-Al2O 3, respectively. On the basis of the experimental results and literature data, the potential mechanisms for heterogeneous decomposition of H2O2 were proposed, and the atmospheric implications of these reactions were discussed. It is found that heterogeneous reaction of H2O2 on both mineral oxides plays a significant role in processing mineral aerosols, although its role as a sink for ambient H 2O2 is probably limited. © 2011 American Chemical Society.