On the impact of heterogeneous chemistry on ozone in the Tropopause Region

Abstract

We examine the impact of heterogeneous chemistry involving liquid aerosol and ice particles on net ozone (O 3) production rates under conditions representative of the midlatitude upper troposphere (UT) and lowermost stratosphere (LS). We demonstrate that heterogeneous effects are controlled by nitrogen oxides (NO x) and by the location of the air masses relative to the tropopause (TP). The net effect of heterogeneous chemistry is to decrease net O 3 production below the TP (via heterogeneous HO 2 loss) and to cause O 3 destruction above the TP (via heterogeneous chlorine (Cl) activation). In the UT, gas phase chemistry due to non-methane hydrocarbons (NMHCs) can become as important for O 3 chemistry as heterogeneous reactions, and removal of HO 2 by particles can become more important than changes of hydrogen oxides (HO x) through heterogeneous bromine (Br) chemistry. In the humid LS, Cl activation can become sufficiently large, so that O 3 depletion occurs at all conceivable values of NO x. Such cold and humid conditions occur frequently enough to reduce the average ozone production rates in the midlatitude LS by more than 10%.