We will comment on recent results from laboratory work and an analysis of in situ data from the SOLVE (Sage III Ozone Loss and Validation Experiment, staged out of Kiruna, Sweden from Nov 1999 to Mar 2000) mission to investigate a systematic error regarding our understanding of the yield of Cl atoms from the titration of ClO with NO. This yield is an input parameter required to calculate the ambient ClO concentration from observed Cl atom fluorescence. The yield is normally calculated using a model, based upon flight conditions of temperature, pressure, flow velocity, [O3], and [NO]. The source of the revision is the inclusion of a mechanism that involves Cl atom loss in our instrument duct due to reaction with O2, and subsequent reaction of the ClOO product with NO. 
The relative importance of the ClOO + NO mechanism is extremely T-dependent due to the thermal instability of ClOO. We have evidence from in situ observations and laboratory work that the rate constant (k) for the ClOO+NO reaction is ~3.0e(-11) (cc/molec sec). Using this value lowers the Cl yield by ~15% at T = 215 K and ~10% at T = 220 K, with respect to a model using k=0. The derived ClO observations are inversely proportional to the yield, thus the ClO observations increase by a similar amount. The expected effect on ClO observations from earlier ER-2 aircraft missions (SPADE, ASHOE/MAESA and POLARIS) will be discussed.