In situ observations of HO 2 and OH obtained on the NASA ER‐2 in the high‐ClO conditions of the 1999/2000 Arctic polar vortex

Abstract

Extensive observations of OH and HO 2 obtained aboard the NASA ER‐2 inside the Arctic polar vortex during the SAGE III Ozone loss and Validation Experiment (SOLVE) provide the opportunity to identify and test interferences during the measurement of HO 2 in the presence of high concentrations of ClO. In‐flight calibrations are consistent with small interferences from CH 3 O 2 (8%) and from ClO (3%) to the total signal on average inside the vortex. Measurements of HO 2 , OH, ClO, and O 3 are used with rate constants derived from laboratory measurements to test the consistency of the reactions that control HO 2 /OH. Inside the vortex the calculated HO 2 /OH under predicts the observed HO 2 /OH by 7% with the JPL‐00 rate constants and over‐predicts the observations by 23% when recent laboratory rates are used. Measurements of HO 2 and ClO are used to calculate ozone loss rates and concentrations of HOCl with uncertainties determined from the analysis of HO 2 /OH. The calculated concentration of HOCl is 52 −28 +50 pptv, or 0.07 × ClO on average in the vortex. The ozone loss rate from the two cycles controlled by HO 2 + ClO is ∼1.5 −0.5 +1.2 ppbv d −1 in early March.