Heterogeneous Interaction of H₂O₂ with Arizona Test Dust

The heterogeneous interaction of H 2 O 2 with solid films of Arizona Test Dust (ATD) was investigated under dark conditions and in presence of UV light using a low pressure flow tube reactor coupled with a quadrupole mass spectrometer. The uptake coefficients were measured as a function of the initial concentration of gaseous H 2 O 2 ([H 2 O 2 ] 0 = (0.18 – 5.1) × 10 12 molecules cm –3 ), irradiance intensity ( J NO 2 = 0.002 – 0.012 s –1 ), relative humidity (RH = 0.002 – 69%), and temperature ( T = 268 – 320 K). The initial uptake coefficient was found to be independent of the concentration of H 2 O 2 and UV irradiation intensity and to decrease with increasing RH and temperature according to the following expressions: γ 0 = 4.8 × 10 –4 /(1+ RH 0.66 ) at T = 275 K and γ 0 = 3.2 × 10 –4 /(1 + 2.5 × 10 10 exp(−7360/T)) at RH = 0.35% (calculated using BET surface area, estimated conservative uncertainty of 30%). By contrast, the steady state uptake coefficient was found to be independent of temperature, to increase upon UV irradiation of the surface, and to be inversely (γ SS ∼ [H 2 O 2 ] −0.6 ) dependent on the concentration of H 2 O 2 . The RH independent steady state uptake coefficient was measured under dark and UV irradiation conditions: γ SS (dark) = (0.95 ± 0.30) × 10 –5 and γ SS (UV) = (1.85 ± 0.55) × 10 –5, for RH = (2 – 69)% and [H 2 O 2 ] 0 ≅ 1.0 × 10 12 molecules cm –3 . The present experimental data support current considerations that uptake of H 2 O 2 on mineral aerosol is potentially an important atmospheric process.