PRODUCTION OF STRATOSPHERIC HNO3 BY DIFFERENT ION-MOLECULE REACTION-MECHANISMS

Precipitation of energetic charged particles into the polar winter str atosphere leads to an enhancement of nitric acid. Three different ion- molecule reaction mechanisms have been suggested as the cause of the H NO3 enhancement: 1) OH production by ion-molecule reactions and subseq uent reaction with NO2 to produce HNO3, 2) positive ion-negative ion r ecombination, and 3) positive hydrated ion reaction with N2O5. It is s hown that the OH reaction can be disregarded. While H+(H2O)(n) + N2O5 may be important below 40 km, it accounts for less than half the HNO3 production at 45 km and is negligible in comparison with ion-ion recom bination at higher altitudes. The inclusion of ion-ion recombination g reatly reduces the ion pair production requirements for HNO3 productio n.