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The Improved Limb Atmospheric Spectrometer (ILAS) on board the Advanced Earth Observing Satellite (ADEOS) measured nitrogen dioxide (NO2) and nitric acid (HNO3) profiles from November 1996 to June 1997 at high latitudes in both hemispheres. The ILAS NO2profiles (version 5.20) are compared with those obtained by balloon‐borne and satellite measurements to validate ILAS NO2data. Comparisons with balloon‐borne measurements indicate that ILAS NO2at 25–30 km has a positive bias of 0.3–0.4 ppbv (6–11%). The random difference in NO2at 25–30 km is 0.2–0.3 ppbv (3–9%). The random error in the ILAS NO2measurements is larger than 100% below 20 km and above 45 km, where the NO2mixing ratios were less than 1.0 ppbv. It is possible that ILAS NO2values were lowered by optically thick aerosols with aerosol extinction coefficients at 780 nm of greater than 0.001 km−1. The lack of diurnal correction along the line of sight contributes to the positive bias in the ILAS NO2values below 25 km. Agreement of the ILAS NO2values with those by the Polar Ozone and Aerosol Measurement (POAM) II instrument is within 10–30% at 25–35 km. The agreement with the Halogen Occultation Experiment (HALOE) is as good as ±10% at 25–40 km. ILAS HNO3(version 5.20) agrees with balloon‐borne HNO3to within 0.1 ppbv (0–1%), and the random difference is within 10% at 25–30 km.

A balloon‐borne UV–visible spectrometer, the SAOZ‐BrO, has been designed for the measurement of BrO on small and relatively low‐cost balloons. It allows the retrieval of the vertical BrO profile with a resolution of 1 km, a precision of 0.5–2 pptv (below 25 km), and a +5/−10% accuracy during the daytime balloon ascent. Fifteen successful flights have been carried out since 1997. Significant BrO amounts were observed at all latitudes and seasons, with a peak concentration altitude varying from 15 km in the winter vortex to 22 km in the tropics. The mixing ratio increases steadily from the tropopause to 25–30 km, depending on the latitude, above which it remains constant up to 30 km. The latitudinal and seasonal changes (maximum at high latitude and in the winter) are largely controlled by the vertical transport of total inorganic bromine and to a smaller extent by photochemistry. Photochemical changes are primarily related to NO2abundances. On a constant potential temperature surface, the BrO mixing ratio is the largest in Polar Regions in the winter, where NO2is nearly absent. In contrast, BrO is the smallest during the polar day and in the summer at midlatitude. The presence of activated chlorine in the cold vortex has little impact on BrO abundances. Finally, significant amounts were observed in the upper troposphere: (1) in the summer at midlatitude where it was the result of a stratosphere–troposphere exchange (STE) event advecting bromine from the stratosphere and (2) at the tropics where its presence is likely due to the conversion of organic bromine at lower altitude.

Vertical profiles of ozone concentration in the high latitudes were observed by the Improved Limb Atmospheric Spectrometer (ILAS) aboard the Advanced Earth Observing Satellite (ADEOS) from November 1996 to June 1997. The ozone data obtained by the version 5.20 ILAS retrieval algorithm are compared with those obtained by the version 19 Halogen Occultation Experiment (HALOE), the version 6 Stratospheric Aerosol and Gas Experiment (SAGE) II, and the version 6 Polar Ozone and Aerosol Measurement (POAM) II retrieval algorithms. The ILAS data are also compared with ozone data measured by ozonesondes, instruments on board balloons or an aircraft, and ground‐based instruments. The ILAS ozone data generally agree with its correlative data between 11 and 64 km with some exceptions. Quantitatively, the median value of the relative difference (absolute difference divided by its mean value) for these comparisons was within ±10%. Relative differences (18%) exceeding the combined measurement errors were found around 45–55 km altitude from comparisons with the HALOE and SAGE II data in January 1997 in the Southern Hemisphere (SH). Larger relative differences (around 50%) were also found below 15 km from comparisons with the HALOE and POAM II data in November 1996 in the SH, but these absolute differences were 0.10–0.16 ppmv as the median value. The ozone data processed by the version 5.20 were improved compared to the former version 3.10, which is available to the general public. The version 5.20 ozone data can be used for scientific analysis purposes based on the accuracy of the data in comparison with these other instruments.