Measurements of stratospheric HO2 and NO2 by matrix isolation and ESR spectroscopy

Vertical profiles of stratospheric HO2 and NO2 concentrations were determined using matrix isolation and electron spin resonance spectroscopy (ESR). Up to 10 different samples per flight were collected in situ by a balloon-borne cryosampler. Free radicals and trace constituents which are condensable at 68 K are trapped in a polycrystalline H2O or D2O matrix. After collection, the samples are stored at a temperature below 83 K until they are analyzed in the laboratory by X-band ESR spectroscopy at 4 K. The HO2 and NO2 were identified and calibrated by comparison with standard samples collected in the laboratory under typical stratospheric sampling conditions. From several flights over southern France (44 deg N) two profiles of the stratospheric NO2 mixing ratio were obtained. One, from October 21, 1982, agrees well with previous measurements. The other, from October 8, 1981, is lower by one order of magnitude. The few HO2 data obtained around 35 km altitude agree with previous measurements. An isolated measurement at 17 km altitude is one order of magnitude higher than the model predicted HO2 concentration.