The mass accommodation coefficient of ozone on an aqueous surface
Abstract
A wetted-wall cylindrical flow reactor was used to measure uptake coefficients, γ, of O3 on aqueous surfaces at 293 K. The loss of O3 from the gas-phase following contact with varying areas of aqueous surface was determined by UV absorption. The use of Na2S2O3 as an aqueous-phase scavenger for O3 ensured that uptake coefficients were in a reaction-controlled rather than mass accommodation-controlled regime. Observed uptake coefficients were corrected for radial gas-diffusion to yield values of γcorr. From extrapolation of a plot of 1/γcorr against the inverse square-root of the Na2S2O3 activity, a value of α = 4 × 10−2 was derived for the true mass accommodation coefficient of O3. Evaluation of uncertainties indicate a conservative lower limit of 10−2 for α. The data do not rule out that the upper limit approaches unity. However, it is shown that the measured value of α is sufficiently high that mass accommodation does not limit heterogeneous processing of O3 in the atmosphere for droplets of diameter >10 μm. A value of 3.7+0.7−0.6 × 108 L mol−1 s−1 is derived for the aqueous-phase reaction rate coefficient between O3 and Na2S2O3 at 293 K.