During three missions in 1992, 1993, and 1994, the Millimeter‐wave Atmospheric Sounder (MAS) measured volume mixing ratio profiles of stratospheric chlorine monoxide (ClO) at 204 GHz from the space shuttle. Owing to the space shuttle orbit, measurements were restricted to tropical and midlatitudes. We compared zonal mean profiles to correlative ClO measurements by an airborne 649 GHz radiometer, a ground‐based 278 GHz instrument on Mauna Kea, Hawaii, and Version 4 ClO profiles by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS). The agreement between MAS and all the other instruments was well within the combined error bars over a pressure range of 0.4–40 hPa. Further comparisons of MAS and MLS day‐night difference profiles produced an agreement of typically better than 0.1 ppbv. A detailed analysis proved that this agreement was independent of the a priori information that was used for the retrieval of the different data sets.

This paper discusses the validation of measurements of O3 distribution in the Earth's atmosphere made by the Millimeter‐wave Atmospheric Sounder (MAS), a component of NASA's ATLAS spacelab shuttle package. Measurements of 184 GHz O3 emission from the Earth's limb at tangent altitudes between 20 and 80 km were made with a 50 channel radiometer having a spectral resolution of 200 KHz. In three missions the emissions of O3, H2O, ClO, and O2 were measured between 70°S and 70°N latitudes. O3 mixing ratio calculations and error analysis were performed with the Rodgers optimal estimation method. Data binned in 128 s batches yield mixing ratio profiles with an altitude resolution of 7 km at the O3 peak and an estimated accuracy of 5%. Additional retrievals made with all data from each mission binned in 5° latitude zones yield mixing ratios with about 5 km altitude resolution and somewhat improved accuracy. Comparisons with coincident measurements from other space platforms indicate a general agreement within approximately 5%. The data are publicly available through the German Remote Sensing Data Center.

We present an overview of Polar Ozone and Aerosol Measurement (FOAM) II satellite-based observations of ozone in the Antarctic ozone hole in 1994, 1995, and 1996. The FOAM II observations are consistent with previous observations suggesting that ozone loss in the ozone hole is confined to the polar vortex. Ozone concentrations are observed to decrease by nearly a factor of 10 near 20 km during the ozone hole formation period, and a reduction in ozone was observed up to 24 km. The timing of ozone loss and recovery was similar in each year. Ozone concentrations begin to decrease in July, and the period of largest depletion observed by FOAM II occurs between early September and early October, when the observations are obtained at high southern latitudes (82(0)-88(0)S) near the vortex center. However, ozone concentrations were consistently lower (by about 10%) in 1996, throughout the atone hole altitude region and time period, than in the other two years. We have also used the POAM II observations to compute vertical profiles of monthly averaged ozone photochemical loss rates as a function of potential temperature in August (450-800 K); and September (450-700 K) of each year, incorporating a correction for diabatic descent. We find that the ozone loss rates are not significantly different from zero in August 1994 at any potential temperature level. However, we do find significant chemical loss in August 1995 below 600 K, and in August 1996 at all levels up to 700 K. Maximum monthly averaged ozone chemical loss rates occurred in September near 500 K in each year (1994: 0.1 +/- 0.004 parts per million by volume per day (ppmv/d); 1995 and 1996: 0.08 +/- 0.004 ppmv/d). Generally, in September, loss rates were larger in 1994 than in 1995 and 1996 below 550 K, and above 550 K the largest loss rates occurred in 1996. We find significant chemical loss up to at least 706 K in September in all three years. Finally, the FOAM II observations show that in late spring, after the ozone hole chemical processing has been completed, ozone mixing ratios are lower inside the Antarctic vortex (relative to outside the vortex) at all levels between at least 450 K and 1500 K, presumably resulting from a combination of dynamical and chemical effects.

Measured stratospheric mixing ratios of HCl, ClNO3, and ClO from ATMOS and MAS are poorly reproduced by models using recommended kinetic parameters. This discrepancy is not resolved by new rates for the reactions Cl+CH4 and OH+HCl derived from weighted fits to laboratory measurements. A deficit in modeled [HCl] and corresponding overprediction of [ClNO3] and [ClO], which increases with altitude, suggests that production of HCl between 20 and 50 km is much faster than predicted from recommended rates.

Volume mixing ratio (VMR) profiles of the chlorine‐bearing gases HCl, ClONO2, CCl3F, CCl2F2, CHClF2, CCl4, and CH3Cl have been measured between 3 and 49° northern‐ and 65 to 72° southern latitudes with the Atmospheric Trace MOlecule Spectroscopy (ATMOS) instrument during the ATmospheric Laboratory for Applications and Science (ATLAS)‐3 shuttle mission of 3 to 12 November 1994. A subset of these profiles obtained between 20 and 49°N at sunset, combined with ClO profiles measured by the Millimeter‐wave Atmospheric Sounder (MAS) also from aboard ATLAS‐3, measurements by balloon for HOCl, CH3CCl3 and C2Cl3F3, and model calculations for COClF indicates that the mean burden of chlorine, ClTOT, was equal to (3.53±0.10) ppbv (parts per billion by volume), 1‐sigma, throughout the stratosphere at the time of the ATLAS 3 mission. This is some 37% larger than the mean 2.58 ppbv value measured by ATMOS within the same latitude zone during the Spacelab 3 flight of 29 April to 6 May 1985, consitent with an exponential growth rate of the chlorine loading in the stratosphere equal to 3.3%/yr or a linear increase of 0.10 ppbv/yr over the Spring‐1985 to Fall‐1994 time period. These findings are in agreement with both the burden and increase of the main anthropogenic Cl‐bearing source gases at the surface during the 1980s, confirming that the stratospheric chlorine loading is primarily of anthropogenic origin.

Ozone profile measurements were made by three instruments, ATMOS, MAS, and SSBUV, using distinctly different observing techniques, as part of the ATLAS Space Shuttle missions in March 1992, April 1993, and November 1994. ATMOS makes solar-occultation observations of infrared spectra using a Fourier transform interferometer. MAS uses a limb-scanning antenna to measure emission spectra at millimeter wavelengths. SSBUV is a nadir-viewing instrument measuring the transmission of scattered solar ultraviolet radiation modified by ozone absorption. A sample of zonal-mean mixing ratio profiles indicates that these three ATLAS instruments generally agree to within 10%, although a few potential biases have been noted. There are significant differences in the character of the agreement between ATLAS 1 and ATLAS 2 which will require further study.

We present measurements of the latitudinal variation of nighttime O3 and H2O in the mesosphere and (for O3) lower thermosphere obtained with the Millimeter‐wave Atmospheric Sounder (MAS) instrument during the ATLAS 2 mission (8–15 April 1993). These are the first such measurements that have ever been reported. They indicate an O3 mixing ratio minimum at mid‐latitudes in the upper mesosphere, with maxima in the tropics and at high latitudes. The H2O retrievals indicate H2O mixing ratios decreasing toward the poles in both hemispheres in the upper mesosphere. We also present measurements of the diurnal variation of O3 at southern mid‐latitudes, at higher vertical resolution than has ever been reported previously. The results are generally consistent with previous measurements and modeling studies.

The Millimeter-Wave Atmospheric Sounder (MAS) is a shuttle-based limb-sounding instrument designed for global spectroscopic studies of O-3, and constituents important in O-3 photochemistry, in the middle atmosphere. It is part of the NASA's Atmospheric Laboratory for Applications and Science (ATLAS) spacelab shuttle mission. This paper presents an overview of the instrument, operation, and data analysis. In addition, as an example of the results, we present zonal average retrievals for O-3, H2O, and ClO obtained in ATLAS 1. The MAS O-3 and H2O measurements are shown to agree well with simultaneous observations made with the UARS MLS instrument.

We report on stratospheric and mesospheric water vapor (H2O) observations obtained by the Millimeter wave Atmospheric Sounder (MAS) in the Arctic spring of 1992. In the lower stratosphere, the observations show enhanced H2O inside the vortex between 450 K and 625 K, in agreement with other H2O observations. In the upper stratosphere and lower mesosphere, at potential temperatures between 1850 K and 2200 K, we find regions of depressed H2O volume mixing ratio coincident with remnants of high potential vorticity. The depressed mesospheric H2O, as well as the enhanced lower stratospheric H2O, are consistent with wintertime descent. It also suggests effective containment of air up into the lower mesosphere.

Latitudinal distributions of upper stratospheric ClO measured by MAS during the three ATLAS missions are presented for northern hemisphere (NH) spring equinox in 1992, southern hemisphere (SH) early fall in 1993, and NH fall in 1994. The MAS ClO results are shown along with correlative MLS observations. The results of both instruments consistently show the same latitudinal features. The ClO maximum in the NH spring occurs at mid latitudes, whereas the latitudinal ClO maximum in both the NH and SH fall occurs at high latitudes. The volume mixing ratio maxima were significantly higher in the fall (0.7–0.8 ppbv) than in spring (0.5–0.6 ppbv). Qualitatively, these results are consistent with calculations of several 2‐D models.

We report on observations of the J = 1 → 0 emission line of terrestrial mesospheric CO at 115 GHz. The measurements were made in the fall of 1993 and in February 1994 from Bern (47°N, 7.5°E). Column densities above 65 km as well as mesospheric vertical distributions were derived from the measured spectra. Between the end of September and middle November an increase by a factor of 2 of the column density was detected, in accordance with theory and previous observations. The February measurements exhibited a short‐term variation on a timescale of a few days which may be explained by a combination of horizontal advection of air and gravity wave activity.

The Millimeter wave Atmospheric Sounder (MAS) uses the limb sounding principle to detect atmospheric emission lines in the frequency range from 60 GHz to 205 GHz. MAS was flown for the first time during the ATLAS-1 mission in March 1992. The flight altitude of 300 km and an inclination of the orbit of 57° allowed to take measurements of ozone, water-vapor and chlorine monoxide (ClO) from 70°S to 70°N during day and night. The authors report on first results from measurements of the pressure broadened ClO-transitions around 204.352 GHz. As ClO exhibits a strong diurnal variability, vanishing during the night at most altitudes, the authors subtracted night spectra from day spectra in order to remove systematic errors and baseline ripple. Retrieval of ClO abundances has been performed in two ways. The difference spectra have been inverted by using the optimal estimation technique and information from apriori abundance profiles. This resulted in five independent layers of the retrieved ClO volume mixing profile, zonally averaged for latitudinal bands of 15°. On the other hand the total integrated spectral intensity has been determined for approx. 80 MHz around the center of the line. The spectral intensity is proportional to the column density along the path. This spectral intensity has been determined for 3 km thick layers in an onion peeling approach for an ideal pencil beam

A rigorous error analysis is applied to the retrieval of chlorine monoxide (ClO), ozone (O 3 ), and water vapor (H 2 O) profiles from millimeter wave spectra measured with a limb sounding instrument at 204, 184, and 183 GHz. The effect of different height resolutions on the accuracy and precision is studied. The nature of the different error sources and their contributions to the total error are discussed. A quantitative analysis for a specific limb sounding experiment, the MAS on the ATLAS spacelab shuttle program, is presented. The accuracy of the profiles to be retrieved is 30% for ClO around 35 km (for an altitude resolution of 5 km and an integration time of 200 s per tangent height). O 3 can be retrieved at an accuracy of 5 to 9% between 18 and 60 km (3 km; 1–100 s, depending on height). H 2 O can be retrieved at an accuracy of 4 to 9% between 20 and 75 km (3 km; 1–100 s). For O 3 , measurements at a resolution of 1 km are possible between 18 and 50 km, for H 2 O between 20 and 60 km.

The Millimeter Wave Atmospheric Sounder (MAS) will be launched in the spring of 1992 as part of the ATLAS 1 (Atmospheric Laboratory for Application and Science) mission. Using passive limb-scanning millimeter-wave radiometry, it will sense the thermal emission produced by ozone at 184 GHz, water vapor at 183 GHz, chlorine monoxide at 204 GHz, and oxygen (for retrieval of temperature and pressure) at 60 GHz. From these observations, concentration profiles of these gases throughout the middle atmosphere will be made. The fundamentals of the measurements, the design of the radiometers, and the approaches used for the data analysis are described