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

Unexpected high levels of OH and NO were recorded at the South Pole (SP) Atmospheric Research Observatory during the 1998–99 ISCAT field study. Model simulations suggest a major photochemical linkage between observed OH and NO. A detailed comparison of the observations with model predictions revealed 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 underestimated OH at levels >380 pptv. The reasons for these deviations appear not to involve NO directly but rather HO_x radical scavenging for the low NO conditions and additional HO_x sources for the high NO conditions. Because of the elevated levels of NO and highly activated HO_x photochemistry, the SP was found to be a strong net source of surface ozone. It is quite likely that the strong oxidizing environment found at the South Pole extends over the entire polar plateau.