Heterogeneous interaction of H2O2 with Arizona Test Dust.

ABSTRACT

The heterogeneous interaction of H2O2 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 H2O2 ([H2O2]0 = (0.18 - 5.1) × 10(12) molecules cm(-3)), irradiance intensity (JNO2 = 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 H2O2 and UV irradiation intensity and to decrease with increasing RH and temperature according to the following expressions γ0 = 4.8 × 10(-4)/(1+ RH(0.66)) at T = 275 K and γ0 = 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 (γSS ∼ [H2O2](-0.6)) dependent on the concentration of H2O2. The RH independent steady state uptake coefficient was measured under dark and UV irradiation conditions γSS(dark) = (0.95 ± 0.30) × 10(-5) and γSS(UV) = (1.85 ± 0.55) × 10(-5), for RH = (2 - 69)% and [H2O2]0 ≅ 1.0 × 10(12) molecules cm(-3). The present experimental data support current considerations that uptake of H2O2 on mineral aerosol is potentially an important atmospheric process.