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This paper describes the All Sky Infrared Visible Analyzer (ASIVA), a multi-purpose visible and infrared sky imaging and analysis instrument whose primary function is to provide radiometrically calibrated imagery in the mid-infrared (mid-IR) atmospheric window. This functionality enables the determination of diurnal fractional sky cover and estimates of sky/cloud temperature from which one can derive estimates of sky/cloud emissivity and cloud height. This paper describes the calibration methods and performance of the ASIVA instrument with particular emphasis on data products being developed for the meteorological community. Data presented here were collected during the Solmirus' ASIVA campaign conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Climate Research Facility from 21 May to 27 July 2009. The purpose of this campaign was to determine the efficacy of IR technology in providing reliable nighttime sky cover data. Significant progress has been made in the analysis of the campaign data over the past several years and the ASIVA has proven to be an excellent instrument for determining sky cover as well as the potential for determining sky/cloud temperature, sky/cloud emissivity, precipitable water vapor (PWV), and ultimately cloud height.

This article describes a novel calibration method developed for the All Sky Infrared Visible Analyzer (ASIVA). This instrument is principally designed to characterize sky conditions for purposes of improving ground-based astronomical observational performance. Calibration and detection performance of the ASIVA's mid-infrared camera subsystem with particular emphasis on data products that are being developed to quantify photometric quality are described in detail. This analysis allows for the determination of a sky quality metric that can serve as a consistent and reliable metric for telescope scheduling purposes.

Time series of total column abundances of hydrogen chloride (HCl), chlorine nitrate (ClONO2), and hydrogen fluoride (HF) were determined from ground-based Fourier transform infrared (FTIR) spectra recorded at 17 sites belonging to the Network for the Detection of Atmospheric Composition Change (NDACC) and located between 80.05° N and 77.82° S. By providing such a near-global overview on ground-based measurements of the two major stratospheric chlorine reservoir species, HCl and ClONO2, the present study is able to confirm the decrease of the atmospheric inorganic chlorine abundance during the last few years. This decrease is expected following the 1987 Montreal Protocol and its amendments and adjustments, where restrictions and a subsequent phase-out of the prominent anthropogenic chlorine source gases (solvents, chlorofluorocarbons) were agreed upon to enable a stabilisation and recovery of the stratospheric ozone layer. The atmospheric fluorine content is expected to be influenced by the Montreal Protocol, too, because most of the banned anthropogenic gases also represent important fluorine sources. But many of the substitutes to the banned gases also contain fluorine so that the HF total column abundance is expected to have continued to increase during the last few years. The measurements are compared with calculations from five different models: the two-dimensional Bremen model, the two chemistry-transport models KASIMA and SLIMCAT, and the two chemistry-climate models EMAC and SOCOL. Thereby, the ability of the models to reproduce the absolute total column amounts, the seasonal cycles, and the temporal evolution found in the FTIR measurements is investigated and inter-compared. This is especially interesting because the models have different architectures. The overall agreement between the measurements and models for the total column abundances and the seasonal cycles is good. Linear trends of HCl, ClONO2, and HF are calculated from both measurement and model time series data, with a focus on the time range 2000–2009. This period is chosen because from most of the measurement sites taking part in this study, data are available during these years. The precision of the trends is estimated with the bootstrap resampling method. The sensitivity of the trend results with respect to the fitting function, the time of year chosen and time series length is investigated, as well as a bias due to the irregular sampling of the measurements. The measurements and model results investigated here agree qualitatively on a decrease of the chlorine species by around 1% yr−1. The models simulate an increase of HF of around 1% yr−1. This also agrees well with most of the measurements, but some of the FTIR series in the Northern Hemisphere show a stabilisation or even a decrease in the last few years. In general, for all three gases, the measured trends vary more strongly with latitude and hemisphere than the modelled trends. Relative to the FTIR measurements, the models tend to underestimate the decreasing chlorine trends and to overestimate the fluorine increase in the Northern Hemisphere. At most sites, the models simulate a stronger decrease of ClONO2 than of HCl. In the FTIR measurements, this difference between the trends of HCl and ClONO2 depends strongly on latitude, especially in the Northern Hemisphere.

In this paper we report on a study conducted using the Middle Atmospheric Nitrogen TRend Assessment (MANTRA) balloon measurements of stratospheric constituents and temperature and the Canadian Middle Atmosphere Model (CMAM). Three different kinds of data are used to assess the inter-consistency of the combined dataset: single profiles of long-lived species from MANTRA 1998, sparse climatologies from the ozonesonde measurements during the four MANTRA campaigns and from HALOE satellite measurements, and the CMAM climatology. In doing so, we evaluate the ability of the model to reproduce the measured fields and to thereby test our ability to describe mid-latitude summertime stratospheric processes. The MANTRA campaigns were conducted at Vanscoy, Saskatchewan, Canada (52° N, 107° W) in late August and early September of 1998, 2000, 2002 and 2004. During late summer at mid-latitudes, the stratosphere is close to photochemical control, providing an ideal scenario for the study reported here. From this analysis we find that: (1) reducing the value for the vertical diffusion coefficient in CMAM to a more physically reasonable value results in the model better reproducing the measured profiles of long-lived species; (2) the existence of compact correlations among the constituents, as expected from independent measurements in the literature and from models, confirms the self-consistency of the MANTRA measurements; and (3) the 1998 measurements show structures in the chemical species profiles that can be associated with transport, adding to the growing evidence that the summertime stratosphere can be much more disturbed than anticipated. The mechanisms responsible for such disturbances need to be understood in order to assess the representativeness of the measurements and to isolate long-term trends.

The MANTRA (Middle Atmosphere Nitrogen TRend Assessment) 2004 campaign took place in Vanscoy, Saskatchewan, Canada (52° N, 107° W) from 3 August to 15 September, 2004. In support of the main balloon launch, a suite of five zenith-sky and direct-Sun-viewing UV-visible ground-based spectrometers was deployed, primarily measuring ozone and NO2 total columns. Three Fourier transform spectrometers (FTSs) that were part of the balloon payload also performed ground-based measurements of several species, including ozone. Ground-based measurements of ozone and NO2 differential slant column densities from the zenith-viewing UV-visible instruments are presented herein. They are found to partially agree within NDACC (Network for the Detection of Atmospheric Composition Change) standards for instruments certified for process studies and satellite validation. Vertical column densities of ozone from the zenith-sky UV-visible instruments, the FTSs, a Brewer spectrophotometer, and ozonesondes are compared, and found to agree within the combined error estimates of the instruments (15%). NO2 vertical column densities from two of the UV-visible instruments are compared, and are also found to agree within combined error (15%).

The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) campaign is intended to address the question of whether possible changes in the mid‐latitude nitrogen budget can account for discrepancies between predicted and observed ozone loss at these latitudes. In addition, MANTRA seeks to establish consistency between old and new measurement techniques. We report here the results of infra‐red spectral measurements made with a high resolution Fourier Transform Spectrometer (FTS) during the August 1998 MANTRA flight. Vertical mixing ratio profiles of methane, nitrous oxide, ozone, nitric acid, hydrogen chloride, CFC‐11 and CFC‐12 are presented. The error estimates on the retrieved values are larger than typical for this type of measurement, due mostly to instrument problems that occurred during flight. In addition, the CFC values are larger than expected. Possible reasons for this are discussed.

The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) series of high‐altitude balloon flights is being undertaken to investigate changes in the concentrations of northern hemisphere mid‐latitude stratospheric ozone, and of nitrogen and chlorine compounds that play a role in ozone chemistry. Four campaigns have been carried out to date, all from Vanscoy, Saskatchewan, Canada (52°01'N, 107°02'W, 511.0 m). The first MANTRA mission took place in August 1998, with the balloon flight on 24 August 1998 being the first Canadian launch of a large high‐altitude balloon in about fifteen years. The balloon carried a payload of instruments to measure atmospheric composition, and made measurements from a float altitude of 32–38 km for one day. Three of these instruments had been flown on the Stratoprobe flights of the Atmospheric Environment Service (now the Meteorological Service of Canada) in the 1970s and early 1980s, providing a link to historical data predating the onset of mid‐latitude ozone loss. The...

A set of previously unpredicted 16O3 strong absorption lines in the 5 μ m region are identified for the first time in balloon-borne high-resolution ( 0.003 cm - 1 ) solar spectra. These spectral features are consistent with recent ozone laboratory spectra, and are interpreted by accidental resonance effects. Some of the lines are also observed in high-resolution ground-based spectra.

Comparisons of chemically active species with chemically inert tracers are useful to quantify transport and mixing and assess the accuracy of model predictions. We report measurements of chemically active species and chemically inert tracers in the stratosphere derived from the analysis of infrared solar absorption spectra recorded with a ground-based Fourier transform spectrometer operated typically at 0.005- to 0.01-cm−1 spectral resolution. The measurements were recorded from Kitt Peak in southern Arizona (latitude 31.9°N, 111.6°W, 2.09 km altitude). Time series of N2O, CH4, O3, and HNO3 vertical profiles have been retrieved from measurements in microwindows. From these results, correlations between N2O and CH4 stratospheric mixing ratios and between O3 and HNO3 lower stratospheric mixing ratios have been derived. The measured correlations between N2O versus CH4 mixing ratios are compact and show little variability with respect to season in quantitative agreement with Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) spring and autumn measurements recorded near the same latitude. Lower stratospheric O3 versus HNO3 mixing ratios measured during low to moderate aerosol loading time periods also show a compact relations though the HNO3/O3 slope is a factor of 2 lower than obtained from November 1994 ATMOS measurements near the same latitude. We also compare Kitt Peak and ATMOS N2O versus CH4 and O3 versus HNO3 relations obtained by averaging the measurements over two broad stratospheric layers. This comparison avoids bias from the a priori profiles and the limited vertical resolution of the ground-based observations.

The Improved Limb Atmospheric Spectrometer (ILAS), a solar occultation infrared satellite sensor, was launched in August 1996. The ILAS validation balloon campaigns were carried out from Kiruna, Sweden (68°N, 21°E), in February and March 1997 and Fairbanks, Alaska (65°N, 148°W), in April and May 1997. During these campaigns, measurements of nitric acid (HNO3) were made using infrared emission spectrometers (Cold Atmospheric Emission Spectral Radiometer, Michelson Interferometer for Passive Atmospheric Sounding-Balloon-Borne version 2, and farinfrared spectrometer) and infrared solar occultation spectrometers (Limb Profile Monitor of the Atmosphere and Mark IV interferometer). An in situ experiment (Chemiluminescence Detector) measured total reactive nitrogen (NOy,), from which HNO3 mixing ratios in the lower stratosphere were calculated. In addition, an in situ NOy, measurement was also made at 12 km altitude from the Deutsche Luft-und Raumfahrt Falcon aircraft in January 1997. The ILAS version 3.10 HNO3 mixing ratios obtained at the nearest location and averaged ILAS mixing ratios obtained within certain criteria were compared with the balloon data. The precision of the ILAS measurements was estimated from the random differences to be 0.8 parts per billion by volume (ppbv), corresponding to about 35% at 15 km and 10–15% at 20–35 km. While the absolute accuracy estimated from the systematic differences was as good as 0.5 ppbv (5%) at 20 km, the ILAS HNO3 mixing ratios were systematically lower than the balloon values by 1 ppbv (15–20%) at 25–30 km. The error in the altitude registration in the ILAS retrieval algorithm is a possible cause for the negative bias at higher altitudes.

High spectral resolution (0.003/ cm) infrared solar absorption measurements of CO, C2H6, and HCN have been recorded at the Network for the Detection of Stratospheric Change station on Mauna Loa, Hawaii, (19.5 deg N, 155.6 deg W, altitude 3.4 km). The observations were obtained on over 250 days between August 1995 and February 1998. Column measurements are reported for the 3.4 - 16 km altitude region, which corresponds approximately to the free troposphere above the station. Average CO mixing ratios computed for this layer have been compared with flask sampling CO measurements obtained in situ at the station during the same time period. Both show asymmetrical seasonal cycles superimposed on significant variability. The first two years of observations exhibit a broad January-April maximum and a sharper CO minimum during late summer. The C2H6 and CO 3.4 - 16 km columns were highly correlated throughout the observing period with the C2H6/CO slope intermediate between higher and lower values derived from similar infrared spectroscopic measurements at 32 deg N and 45 deg S latitude, respectively. Variable enhancements in CO, C2H6, and particularly HCN were observed beginning in about September 1997. The maximum HCN free tropospheric monthly mean column observed in November 1997 corresponds to an average 3.4 - 16 km mixing ratio of 0.7 ppbv (1 ppbv = 10(exp -9) per unit volume), more than a factor of 3 above the background level. The HCN enhancements continued through the end of the observational series. Back-trajectory calculations suggest that the emissions originated at low northern latitudes in southeast Asia. Surface CO mixing ratios and the C2H6 tropospheric columns measured during the same time also showed anomalous autumn 1997 maxima. The intense and widespread tropical wild fires that burned during 3 the strong El Nino warm phase of 1997-1998 are the likely source of the elevated emission products.

Total column abundances of CHClF2 (HCFC-22) have been retrieved from high-resolution infrared solar absorption spectra recorded at the Network for the Detection of Stratospheric Change (NDSC) station in Lauder, New Zealand (370 m altitude, 45.04°S latitude, 169.68°E longitude). The analysis, based on nonlinear least squares fittings to the unresolved 2v6 band Q branch of CH35ClF2 at 829.05 cm−1, has been applied to a time series of 670 spectra recorded on 394 days between May 1985 and November 1994. The measurements indicate exponential and linear (referenced to the beginning of 1994) increase rates of (7.5±0.3)% yr−1 and (5.9±0.2)% yr−1, 1 σ, corresponding to a doubling of the total column abundance over the 9.5-year measurement period. Of the two models the exponential increase model yields a slightly better fit to the data than the linear model. A HCFC-22 south/north hemispheric ratio of 0.83 ±0.04, 1σ, is derived by comparing the Lauder column measurements with column measurements from the International Scientific Station of the Jungfraujoch (46.5°N, 8.0°E), after correction for the altitude difference between the two sites. Using a second, independent method in which the N2O column serves as a surrogate air mass, we have used the Lauder measurements and similar measurements from Table Mountain (34.4°N) to calculate a south/north ratio of 0.91±0.10.

The All Sky Infrared Visible Analyzer (ASIVA) is an instrument principally designed to characterize sky con- ditions for purposes of improving ground-based astronomical observational performance. The ASIVA's primary functionality is to provide radiometrically calibrated imagery across the entire sky over the mid-infrared (IR) spectrum (8-13 μm). Calibration procedures have been developed for purposes of quantifying the photometric quality of the sky. These data products are used to provide the STELLA scheduler with real-time measured conditions of the sky/clouds, including thin cirrus to better optimize observing strategy. We describe how this can be used in the denition of the observing programs to make best use of the telescope time. Additional research is underway to correlate infrared spectral radiance with visible-spectrum extinction.

Using Fourier transform spectra recorded at 25 and 12 μm, it has been possible to perform the first analysis of the 3ν9 − 2ν9, 3ν9 − ν5 and 3ν9 − ν9 hot bands of HNO3 located at 392.4 cm−1, 409.8 cm−1, and 830.4 cm−1, respectively. An accurate description of the torsional splitting in the v9 = 3 vibrational state was achieved, leading to the determination of the two torsional band centers Evg=3,1 = 1288.8451 cm−1 and Evg = 3,2 = 1288.9036 cm−1 and to the first determination of the ν9 torsional potential of HNO3. Finally, the 4ν9 − 3ν9, ν5 + ν9 − 2ν9, and ν5 + ν9 − ν9 hot bands were identified for the first time at 375.3-376.1 cm−1, 447.2 cm−1 and 885.424 cm−1 respectively.

High-resolution Fourier transform spectra covering the 720-920 cm −1 spectral region have been used to perform a reanalysis of the ν 2 band ((010)-(000) vibrational transition) together with the first analysis of the 2ν 2 - ν 2 hot band of nitrogen dioxide ((020)-(010) vibrational transition). The high-quality spectra show that, for numerous ν 2 lines, the hyperfine structure is easily observable in the case of resonances due to the hyperfine Fermi-type operator. By performing a full treatment of the spin-rotation and of the hyperfine operators, a new line list of the ν 2 band (positions and intensities) has been generated, and it is in excellent agreement with the experimental spectrum. Also, a thorough analysis of the 2ν 2 - ν 2 hot band has been performed leading to an extended set of new (020) spin-rotation levels. These levels, together with the {(100), (020), (001)} spin-rotation levels deduced previously from the analysis of the ν 1 , 2ν 2 , and ν 3 cold bands performed in the 6.3- to 7.5-μm spectral range [A. Perrin, J.-M. Flaud, C. Camy-Peyret. A.-M. Vasserot, G. Guelachvili, A. Goldman, F. J. Murcray, and R. D. Blatherwick, J. Mol. Spectrosc. 154, 391-406 (1992)] were least-squares fitted, allowing one to derive a new set of vibrational band centers and rotational, spin-rotation, and interaction constants for the {(l00)(020)(001)} interacting states of 14 N 16 O 2 .

Atmospheric and laboratory atlases of high-resolution infrared absorption spectra have been generated from data obtained with the University of Denver Michelson-type interferometer balloon-borne spectrometer systems. The main objectives of the atlas work have been the identification and the detailed analysis of stratospheric infrared high-resolution spectral features. The stratospheric atlases cover many spectral intervals and provide tables of line positions and species identifications. High Sun spectra are used for identification of solar lines. Latest editions of these atlases include selected sections in the 760-1950- and 800-1700-cm(-1) regions at 0.02- and 0.002-cm(-1) resolutions, respectively. In addition to the stratospheric atlases, ground-based and laboratory spectral atlases have also been produced. The laboratory spectra of many molecules relevant to stratospheric chemistry have been obtained. A number of ongoing spectroscopic studies have been developed on the basis of the atlas work, including studies of solar and atmospheric spectral features.

New measurements and analysis of high resolution(0.0025 cm(-1)) laboratory spectra of the carbonyl fluoride v6 band are described. The data are used to generate line parameters suitable for high resolution atmospheric studies.

A new atlas of CH(4) lines in the 1120-1800-cm(-1) region has been generated, based on laboratory spectra taken with a Nicolet interferometer at 0.06-cm(-1) resolution with 635-cm path length at pressures of 0.98 Torr, 4.86 Torr, and 19.97 Torr. A compilation of line positions and line intensities includes 1339 CH(4) lines, several hundred of which have not been previously observed.

High-resolution Fourier transform spectra have been used in the 1200–1850 cm−1 spectral region to measure the positions of lines with Ka = 0–15 for the ν1 and ν3 bands of 14N16O2, as well as lines with Ka = 0, 1, 2, and 6 for the 2ν2 band up to very high N values. The spin-rotation energy levels were very satisfactorily reproduced using a theoretical model which takes explicitly into account both the Coriolis interactions between the spin-rotation levels of the (001) vibrational state with those of (100) and (020), and the spin-rotation resonances in each vibrational state. In this analysis, precise band centers and rotational, spin-rotation, and coupling constants were obtained for the triad {(100), (020), (001)} of interacting states for 14N16O2. In addition, using a large set of individual line intensities we have determined precisely the ν1, 2ν2, and ν3 transition moment operators of 14N16O2. Finally, a comprehensive list of line positions and intensities of the interacting ν1, 2ν2, and ν3 bands of 14N16O2 has been generated.

Absorption features of the nu(sub 1) band of SO2 have been identified in high resolution infrared solar absorption spectra recorded from Mauna Loa, Hawaii, on July 9 and 12, 1991, shortly after the arrival of the first eruption plume from the Mt. Pinatubo volcano in the Phillipines. A total SO2 vertical column amount of (5.1 +/- 0.5) x 10(exp 16) molecules/sq cm on July 9 has been retrieved based on nonlinear least- squares spectral fittings of 9 selected SO2 absorption features with an updated set of SO2 spectral parameters. A SO2 total column upper limit of 0.9 x 10(esp 16) molecules/sq cm deduced from measurements on September 20-24, 1991, is consistent with the dispersion of the SO2 cloud and the rapid conversion of the SO2 vapor into volcanic aerosol particles.

For monitoring environmental changes, new passive infrared instruments have become available that allow change detection analyses at resolutions and scales that were impossible just a few years ago. Current instruments have been installed in Antarctica will help to better understand the photochemical transport process and accurately predict ozone depletion and climate changes. During the 2003 polar summer one spectrometer was installed at the McMurdo station and another at the South Pole station, for year-around atmospheric chemistry monitoring. These two instruments use the emission technique to deliver high resolution spectra, from which will derive vertical profiles of many atmospheric tracers involved in the ozone destruction process. The first setup uses one channel to acquire the atmospheric data throw two different angles, the second setup uses two simultaneous channels to acquire the data at the same sky angles. Both instruments integrate two black bodies at different temperatures to calibrate the sky data. The data generated will have multipurpose, first is to provide validation for the new generation of the satellite sensors, like the National Polar-orbiting Operation Environmntal Satellite System (NPOESS), second is to allow photochemical transport modelers to compare outputs with actual measurements, and third is to evaluate the trend of some column abundance measurements like HNO 3 , CH 4 , O 3 , CFCs, H 2 O... This paper will present description of the instrumentation, the measurement technique and the automated analysis.

Using a high-resolution (R = 0.0025 cm-1) Fourier transform spectrum of nitric acid recorded at room temperature in the 1100-1240 cm-1 region, it has been possible to perform a more extended analysis of the nu8 + nu9 band of HNO3 centered at 1205.7075 cm-1. As in a recent analysis of this band [W. F. Wang, P. P. Ong, T. L. Tan, E. C. Looi, and H. H. Teo, J. Mol. Spectrosc. 183, 407-413 (1997)], the Hamiltonian used for the line positions calculation takes into account, for the upper state, the DeltaK = +/-2 anharmonic resonance linking the rotational levels of the v8 = v9 = 1 "bright" vibrational state and those of the "dark" v6 = v7 = 1 vibrational state. More than 4800 lines were assigned in the nu8 + nu9 band, which involve significantly higher rotational quantum numbers than in previous works. On the other hand, and surprisingly as compared to previous studies, the nu8 + nu9 band appears to be a hybrid band. In fact, nonnegligible B-type transitions could be clearly identified among the much stronger A-type lines. Accordingly, a set of individual line intensities were measured for lines of both types and were introduced in a least-squares fit to get the A- and B-type components of the transition moment operator. Finally, a synthetic spectrum of the 8.3-µm region of HNO3 has been generated, using for the line positions and line intensities the Hamiltonian constants and the expansion of the transition moment operator which were determined in this work. In this way, the B-type and the A-type components of the nu8 + nu9 band appear to contribute for about (1/4) and (3/4), respectively, to the total band intensity. Copyright 1999 Academic Press.

On 24 July, 1992 and 7 April, 1993, the University of Denver conducted two balloon flights designed to obtain correlative measurements for comparison with the CLAES (Cryogenic Limb Array Etalon Spectrometer) instrument aboard the UARS satellite. These flights were performed using our very high resolution (~0.002 cm-1) Fourier transform interferometer-spectrometer operated in solar occultation mode. We present here the results of this intercomparison for several of the trace species which can be measured with both instruments.

A ground-based solar spectrum at a spectral resolution of about 0.002/cm is used to determine the altitude of the HNO3 layer. The 870/cm spectral region, which is essentially free from absorptions from other species, is employed. The data were obtained with the University of Denver 2.5-m maximum path difference Fourier Transform interferometer spectrometer system. A set of 13 HNO3 vertical profiles were used in the analysis. The best fit obtained for the 'starting' profile (which is centered at 24 km), and the best fit for the profile centered at 26 km are shown. For displacements of greater than 2 km, the discrepancy between the synthetic and observed spectra becomes readily discernible by inspection of the spectra. It is shown that the 'best fit' rms residuals are quite sensitive to the assumed altitude of the HNO3 layer.

Results of ongoing studies of high-resolution solar absorption spectra aimed at the identification and quantification of trace constituents of importance in the chemistry of the stratosphere and upper troposphere are presented. An analysis of balloon-borne and ground-based spectra obtained at 0.0025/cm covering the 700-2200/cm interval is presented. The 0.0025/cm spectra, along with corresponding laboratory spectra, improves the spectral line parameters, and thus the accuracy of quantifying trace constituents. Results for COF2, F22, SF6, and other species are presented. The retrieval methods used for total column density and altitude distribution for both ground-based and balloon-borne spectra are also discussed.

Atmospheric emission spectra obtained with two different spectrometer systems are presented. The first system (the BOMEM Michelson interferometer) is designed for emission work. Spectra were obtained under adverse conditions in the Antarctic, and are still of good absolute accuracy. The second system (a modified Bruker Instruments IFS120 very high spectral resolution interferometer) demonstrates the sensitivity that can be achieved even at higher spectral resolution. This system shows that mid-IR atmospheric emission spectra can be obtained with a good SNR in a reasonable length of time at a relatively high resolution. A properly designed high resolution system should achieve high accuracy, sensitivity, and resolution, thereby permitting measurements of many atmospheric constituents when solar spectra cannot be obtained.

Very-high-resolution FWHM solar-occultation spectra are investigated with a balloon-borne interferometer using revised spectroscopic line parameters for HNO3, O3, and H2O. The O3 and H2O data are evaluated to determine their capacity for interference in the HNO3 line which is studied in the nu sub 2 band at 5.8 microns. The line parameters developed with the stratospheric data are compared to data based on a HITRAN compilation as well as laboratory spectra with a 0.002/cm resolution. The line list is calculated and shown to include J and Ka transitions which improve the line parameters for HNO3 by accounting for the weaker absorption features in the stratospheric spectra. The stratospheric HNO3 profile developed analytically is compared to those based on reported measurements, and the one developed with the stratospheric solar spectra is found to be consistent with the measurements and confirm inherent measurement biases.

A mid IR Michelson interferometer capable of obtaining 0.002-cm(-1) resolution solar spectra has been developed for balloon use. The interferometer is based on the Bomem self-aligning instrument, and is equipped with a solar tracking system, telemetry, and recording systems, as well as temperature control and gondola orientation. The interferometer has made two successful flights in the 7-14 microm (700-1300-cm(-1)) interval up to 40 km. The basic systems are described and sample spectra are presented.

Long-term trends in the concentrations of SF6, CHClF2 (CFC-22), and COF2 in the lower stratosphere have been derived from analysis of ca. 1980 and more recent infrared solar occultation spectra recorded near 32 deg N latitude at approx. 0.02/ cm resolution. Consistent sets of line parameters and spectral calibration methods have been used in the retrievals to minimize systematic error effects. Quoted error limits are 1 sigma estimated precisions. The SF6 and CHClF2 results are based on spectra recorded by balloon-borne interferometers in March 1981 and June 1988 and a comparison of these results with the Atmospheric Trace Molecule Spectroscopy (ATMOS) Experiment/Spacelab 3 measurements obtained in May 1985 near 30 deg N latitude. In the 13-18 km altitude range the mean measured SF6 mixing ratio in parts per trillion by volume (pptv) increased from 1.17 +/- 0.21 in March 1981 to 2.02 +/- 0.20 pptv in June 1988, and the CHClF2 mixing ratio below 15 km altitude increased from 51 +/- 8 pptv in March 1981 to 102 +/- 10 pptv in June 1988. The CHClF2 retrievals used new empirical CHClF2 line parameters derived from 0.03/cm resolution laboratory spectra recorded at six temperatures between 203 and 293 K; the derived mixing ratios are approx. 30% higher than obtained with earlier sets of line parameters, thereby removing a large discrepancy noted previously between IR and in situ measurements of CHClF2. Assuming an exponential growth model for fitting the trends, SF6 and CHClF2 mean increase rates of 7.4% +/- 1.9% and 9.4% +/- 1.3% /year, are obtained, respectively, which correspond to cumulative increases by factors of approx. 1.7 and -2.0 in the concentrations of these gases over the 7.2-year measurement period. Analysis of spectra recorded in October 1979 and April 1989 yields COF2 volume mixing ratios that are respectively 0.44 +/- 0.17 and 1.21 +/- 0.24 times the ATMOS/Spacelab 3 values, from which an average COF2 increase rate of 10.3 +/- 1.8%/ year over this time period has been estimated. The present results are compared with previously reported observations and trends and with one-dimensional model calculations. The model calculated trends are in reasonably good agreement with the observations.

According to models of the photochemistry of the stratosphere, chlorine nitrate (ClONO2) is an important temporary reservoir of stratospheric chlorine. At night, ClO is believed to combine in a three-body reaction with NO2 to form chlorine nitrate. During daylight, chlorine nitrate is destroyed by photolysis to form free chlorine and NO3. Infrared spectroscopy has the potential to provide a technique for conducting important quantitative measurements of stratospheric chlorine nitrate. The present paper reports a detailed study of spectra in the 780/cm region. This study has led to the tentative identification of the nu-4 band Q branch of ClONO2 as a significant contributor to the observed stratospheric absorption near 780.21 per cm.

Infrared solar spectra in the 850 to 1350/cm region, at 0.02/cm resolution, were obtained during a balloon flight made on 27 October 1978 from Alamogordo, New Mexico. Analysis of the 1275-1290/cm region indicates that the atmospheric absorption lines of CH4, N2O, H2O, HNO3 and CO2 near 1283/cm are super-imposed on a broader absorption feature which we interpret as due to the V3 band of CF4. Fine structure of CF4 is also identified. Preliminary estimates from the sunset spectra show approximately 75 pptv CF4 near 25 km.

Ballon-borne infrared solar spectra at about 0.02/cm resolution show a number of atmospheric NO lines isolated from other atmospheric and solar lines in the 1830-1930/cm region. Typical spectra are presented and NO total column values are derived.

A new Michelson-type interferometer system operating in the infrared at very high resolution has been used to record numerous balloon-borne solar absorption spectra of the stratosphere, ground-based solar absorption spectra, and laboratory spectra of molecules of atmospheric interest. In the present work results obtained for several important stratospheric trace gases, HNO3, CIONO2, HO2NO2, NO2, and COF2, in the 8- to 12-micron spectral region are reported. Many new features of these gases have been identified in the stratospheric spectra. Comparison of the new spectra with line-by-line simulations shows that previous spectral line parameters are often inadequate and that new analysis of high-resolution laboratory and atmospheric spectra and improved theoretical calculations will be required for many bands. Preliminary versions of several sets of improved line parameters under development are discussed.

Balloon-borne infrared solar spectra at ∼0.02 cm−1 resolution obtained during sunset are used for the derivation of simultaneous vertical mixing ratio profiles of NO and NO2. A simplified photochemical model for the diurnal variation of NO is included in the analysis.

Recent ground-based infrared solar spectra at 0.02 per cm resolution in the 3000 per cm region have been analyzed for the atmospheric content of HCl. Nonlinear spectral least-squares fitting applied to spectra obtained at several zenith angles shows little sensitivity of the results to tropospheric HCl but provides an accurate measurement of the total column amount.

Infrared atmospheric spectra were obtained at ∼0.02 cm−1 resolution during a balloon flight made on 3/23/81. These spectra show an absorption feature near 829 cm−1 which we identify as due to CHClF2 (Fluorocarbon 22). A preliminary estimate from the sunset spectra shows approximately 100 pptv F-22 near 15 km.

The major components of the Earth's atmosphere, nitrogen, oxygen and argon, are essentially transparent to infrared radiation. Most of the minor and trace gases in the atmosphere have significant infrared absorptions, which provide a means of measuring their abundance. For many years, we have been using the infrared as a remote sensing tool. As Fourier Transform systems (FTS) have developed, they have been increasingly used in our work. We primarily use two techniques for atmospheric measurements: solar absorption spectra and atmospheric emission spectra. In the solar absorption case, the sun is used as an intense source, and the measurement is similar (in principle) to that carried out routinely in the laboratory. Unfortunately, no reference (vacuum) path is readily available, the sample (atmosphere) is not under uniform temperature or pressure conditions and the composition is not uniform. Despite the complications, accurate determinations of gas amounts can be made in many cases, and path lengths unattainable in the laboratory can yield significant information about the molecular spectroscopy of some compounds. Interferometer systems have advantages for recording solar spectra in the infrared: relatively small size for comparable resolution and a highly accurate frequency scale. In most cases there is no multiplex advantage, but the throughput may be higher. FTS can also cover broad spectral intervals, which allows quantification of several gases simultaneously. The atmosphere is a very weak infrared source, and instrument sensitivity is of primary importance. FTS may or may not have a multiplex advantage, but it still provides an accurate frequency scale and substantial throughput.

Infrared atmospheric absorption spectra at 0.02/cm resolution were obtained during a balloon flight on March 23, 1981 from the Holloman AFB, New Mexico. The absorption features, attributed to C2H2, were used to derive a preliminary mixing ratio of about 25 pptv near 9 km, accurate to + or - 40%. This mixing ratio falls into the range of values calculated for the upper troposphere C2H2 in a photochemical/transport model. However, previous measurements from aircraft grab sampling (Cronn and Robinson, 1979) show four to twelve times this C2H2 concentration 1.5 km below the tropopause.

Infrared emission spectra obtained during a balloon flight of the Air Force Geophysics Laboratory Stratospheric Cryogenic Interferometer Balloon Experiment system by the University of Denver are used to measure stratospheric N2O5 after sunrise over New Mexico (latitude 33 deg N). This is the first daytime measurement of N2O5. Comparisons with photochemical modeling show consistency between the observed and predicted decline of N2O5 during the morning hours.

Infrared solar absorption spectra recorded at 0.02/ cm resolution from the National Oceanic and Atmospheric Administration (NOAA) Geophysical Monitoring for Climate Change (GMCC) program station at Mauna Loa, Hawaii (latitude 19.5 deg N, longitude 155.6 deg W, elevation 3.40 km), in February 1997 have been analyzed to determine simultaneous total vertical column amounts for 13 atmospheric gases. Average tropospheric concentrations of CO2, N2O, CH4, and CHCIF2 and the daytime diurnal variations or the total columns of NO and NO2 have also been inferred. The retrieved total columns (in molecules /sq cm) of the nondiurnally varying gases are 1.6 +/- 0.2 x 10(exp 15) for HCl, 5.9 +/- 1.2 x 10(exp 15) for HNO3, 2.0 +/- 0.2 x 10(exp 21) for H2O16, 4.4 +/- 0.7 x 10(exp 18) for H2O18, 2.7 +/- 0.1 x 10(exp 17) for HDO, 2.3 +/- 0.2 x 10(exp 19) for CH4, 5.0 +/- 0.5 x 10(exp 21) for CO2, 6.7 +/- 0.8 x 10(exp 18) for O3, 4.3 +/- 0.4 x 10(exp 18) for N2O, 1.0 +/- 0.2 x 10(exp 16) for C2H6, and 9.7 +/- 2.5 x 10(exp 14) for CHClF2. We compare the total column measurements of HCl and HNO3 with previously reported ground-based, aircraft, and satellite measurements. The results for HCl are or particular interest because of the expected temporal increase in the concentration of this gas in the stratosphere. However, systematic differences among stratospheric HCl total column measurements from 1978 to 1980 and the absence of observations of free tropospheric HCl above Mauna Loa make it impossible to obtain a reliable estimate of the trend in the total burden of HCl. The measured HNO3 total column is consistent with aircraft measurements from approx. 12 km altitude. The O3 total column deduced from the IR spectra agrees with correlative Mauna Loa Umkehr measurements within the estimated error limits. The column-averaged D/H ratio of water vapor is (68 +/- 9) x- 10(exp -6), which is 0.44 +/- 0.06 times the reference value of 155.76 x 10(exp -6) for standard mean ocean water (SMOW). This large depletion in the D content of water vapor is similar to published measurements of the upper troposphere and lower stratosphere. Average tropospheric concentrations deduced for CO2, N2O, and CH4 are in good agreement with correlative NOAA GMCC surface data, indicating consistency between the measurement techniques for determining tropospheric volume mixing ratios. Results of the present study indicate that Mauna Loa is a favorable site for infrared monitoring of atmospheric gases. The site is particularly favorable for monitoring the tropospheric volume mixing ratios of long-lived gases, since the high altitude of the tropopause reduces corrections required to account for the decrease in volume mixing ratio in the stratosphere.

Over 4500 absorption lines have been marked on the spectra and the corresponding line positions tabulated. The associated absorbing telluric or solar species for more than 90% of these lines have been identified and only a fraction of the unidentified lines have peak absorptions greater than a few percent. The high resolution and the low Sun spectra greatly enhance the sensitivity limits for identification of trace constituents.

The effects of changing spectral radiance during the scan of an interferometer on the spectra obtained from the interferogram are considered. For well-behaved variations the integrated radiance and base line are the same as at the zero path difference of the interferometer. The changes in the appearance of spectral features are hardly changed beyond a few resolution elements from the changing features.

Infrared solar spectra were obtained from the ground at McMurdo, Antarctica, during September and October 1987. Absorption features due to HNO3 and HCl have been analyzed to determine the vertical column content of these compounds for the days when observations were made. The variation of these column amounts with time is presented and discussed.