The uptake of HO sub(2) on meteoric smoke analogues

The kinetics of heterogeneous HO sub(2) uptake onto meteoric smoke particles (MSPs) has been studied in the laboratory using analogues of MSP aerosol entrained into a flow tube. The uptake coefficient, gamma , was determined on synthetic amorphous olivine (MgFeSiO sub(4)) to be (6.9 plus or minus 1.2)10 super(-2) at a relative humidity (RH) of 10%. On forsterite (Mg sub(2)SiO sub(4)), gamma =(4.3 plus or minus 0.4)10 super(-3) at RH=11.6% and (7.3 plus or minus 0.4)10 super(-2) at RH=9.9% on fayalite (Fe sub(2)SiO sub(4)). These results indicate that Fe plays a more important mechanistic role than Mg in the removal of HO sub(2) from the gas phase. Electronic structure calculations show that Fe atoms exposed at the particle surface provide a catalytic site where HO sub(2) is converted to H sub(2)O sub(2) via an Eley-Rideal mechanism, but this does not occur on exposed surface Mg atoms. The impact of this heterogeneous process in the middle atmosphere was then investigated using a whole atmosphere chemistry-climate model which incorporates a microphysical treatment of MSPs. Using a global MSP production rate from meteoric ablation of 44t/day, heterogeneous uptake (with gamma =0.2) on MSPs significantly alters the HO sub(x) budget in the nighttime polar vortex. This impact is highly latitude dependent and thus could not be confirmed using currently available satellite measurements of HO sub(2), which are largely unavailable at latitudes greater than 70 degree . Key Points * HO sub(2) uptake coefficients measured on synthetic amorphous olivine particles * Exposed surface Fe atoms appear to catalyze HO sub(2) removal to form H sub(2)O sub(2) * Uptake on meteoric smoke significantly impacts the HO sub(2) atmospheric abundance over the winter poles