An investigation of South Pole HOx chemistry: Comparison of model results with ISCAT observations

Unexpected high levels of OH and NO were recorded at the South Pole (SP) At mospheric Research Observatory during the 1998-99 ISCAT field study. Model simulations suggest a major photochemical linkage between observed OH and N O, A detailed comparison of the observations with model predictions reveale d good agreement for OH at NO levels between 120 and 380 pptv. However, the model tended to overestimate OH for NO levels < 120 pptv, while it underes timated OH at levels > 380 pptv. The reasons for these deviations appear no t to involve NO directly but rather HOx radical scavenging for the low NO c onditions and additional HOx sources for the high NO conditions. Because of the elevated levels of NO and highly activated HOx photochemistry the SP w as found to be a strong net source of surface ozone. It is quite likely tha t the strong oxidizing environment found at the South Pole extends over the entire polar plateau.