Search

We investigate the spatial and temporal distribution of hydrogen cyanide (HCN) in the upper troposphere through numerical simulations and comparison with observations from a space-based instrument. To perform the simulations, we used the Global Environmental Multiscale Air Quality model (GEM-AQ), which is based on the threedimensional Gobal multiscale model developed by the Meteorological Service of Canada for operational weather forecasting. The model was run for the period 2004-2006 on a 1.5deg x 1.5deg global grid with 28 hybrid vertical levels from the surface up to 10 hPa. Objective analysis data from the Canadian Meteorological Centre were used to update the meteorological fields every 24 h. Fire emission fluxes of gas species were generated by using year-specific inventories of carbon emissions with 8-day temporal resolution from the Global Fire Emission Database (GFED) version 2. The model output is compared with HCN profiles measured by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument onboard the Canadian SCISAT-1 satellite. High values of up to a few ppbv are observed in the tropics in the Southern Hemisphere; the enhancement in HCN volume mixing ratios in the upper troposphere is most prominent in October. Low upper-tropospheric mixing ratios of less than 100 pptv are mostly recorded at middle and high latitudes in the Southern Hemisphere in May-July. Mixing ratios in Northern Hemisphere peak in the boreal summer. The amplitude of the seasonal variation is less pronounced than in the Southern Hemisphere. The comparison with the satellite data shows that in the upper troposphere GEM-AQ perform7s well globally for all seasons, except at northern hi gh and middle latitudes in surnmer, where the model has a large negative bias, and in the tropics in winter and spring, where it exhibits large positive bias. This may reflect inaccurate emissions or possible inaccuracies in the emission profile. The model is able to explain most of the observed variability in the upper troposphere HCN field, includin g the interannual variations in the observed mixing ratio. A complementary comparison with daily total columns of HCN from two middle latitude ground-based stations in Northern Japan for the same simulation period shows that the model captures the observed seasonal variation and also points to an underestimation of model emissions in the Northern Hemisphere in the summer. The estimated average global emission equals 1.3 Tg N/yr. The average atmospheric burden is 0.53 Tg N, and the corresponding lifetime is 4.9 months.

High spectral resolution (0.003 per 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, (19.5N, 155.6W, 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 2 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'N and 45'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 the strong El Nino warm phase of 1997- 1998 are the likely source of the elevated emission products.

The final flight of the Atmospheric Trace Molecule Spectroscopy experiment as part of the Atmospheric na Laboratory for Applications and Science (ATLAS-3) Space Shuttle mission in 1994 provided a new opportunity to measure broadband 625-4800/ cm, 2.1 - 16 micron infrared solar spectra at an unapodized resolution of 0.0l/ cm from space. The majority of the observations were obtained as exoatmospheric, of near Sun center, absorption spectra, which were later ratioed to grazing atmospheric measurements to compute the atmospheric transmission of the Earth's atmosphere and analyzed for vertical profiles of minor and trace gases. Relative to the SPACELAB-3 mission that produced 4800 high Sun spectra (which were averaged into four grand average spectra), the ATLAS-3 mission produced some 40,000 high Sun spectra (which have been similarly averaged) with an improvement in signal-to-noise ratio of a factor of 3-4 in the spectral region between 1000 and 4800/ cm. A brief description of the spectral calibration and spectral quality is given as well as the location of electronic archives of these spectra.

Observations inside the November 1994 Antarctic stratospheric vortex and inside the April 1993 remnant Arctic stratospheric vortex by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer are reported. In both instances, elevated volume mixing ratios (VMRS) of carbon monoxide (CO) were measured. A peak Antarctic CO VMR of 60 ppbv (where 1 ppbv = 10(exp -9) per unit Volume) was measured at a potential temperature of 710 K (about 27 km), about 1 km below the altitude of a pocket of elevated NO(y) (total reactive nitrogen) at a deep minimum in N2O (<5 ppbv). The Arctic observations also show a region of elevated vortex CO with a peak VMR of 90 ppbv it 630-670 K (-25 km) but no corresponding enhancement in NO(sub y) perhaps because of stronger dynamical activity in the northern hemisphere polar winter and/or interannual variability in the production of mesospheric or lower thermospheric NO. By comparing vortex and extravortex observations of NO(y) obtained at the same N2O VMR, Arctic vortex denitrification of 5 +/- 2 ppbv at 470 K (at approximately 18 km) is inferred. We show that our conclusion of substantial Arctic winter 1992-1993 denitrification is robust by comparing our extravortex observations with previous polar measurements obtained over a wide range of winter conditions. Correlations of NO(y) with N2O measured at the same potential temperature by ATMOS in the Arctic vortex and at midlatitudes on board the ER-2 aircraft several weeks later lie along the same mixing line. The result demonstrates the consistency of the two data sets and confirms that the ER-2 sampled fragments of the denitrified Arctic vortex following its breakup. An analysis of the ATMOS Arctic measurements of total hydrogen shows no evidence for significant dehydration inside the vortex.

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.

A new technique is presented to determine the degree of denitrification that occured during the 1996/97 Arctic winter, based on balloon and aircraft borne measurements of NOy, N2O and CH4. In this study high-altitude balloon measurements are used to define the properties of air masses that later descend in the polar vortex to altitudes sampled by the ER-2 aircraft and mix isentropically with mid-latitude air.

Atmospheric Trace MOlecule Spectroscopy (ATMOS) measurements made over a wide range of altitudes and latitudes demonstrate compact correlations between mixing ratios of CH, and N,O. Tight but distinct correlations are observed for the tropics, the springtime Arctic vortex, and the extra-tropics/extra-vortex regions, indicating dynamical isolation between these regions. Little variability is apparent in correlations between CH4 and N20 from measurements made in different years (1992, 1993, and 1994), seasons (March/April and November), and hemispheres.

Vertical profiles of infrared cirrus extinction have been derived from tropical and subtropical upper tropospheric solar occultation spectra. The measurements were recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Sciences (ATLAS) 3 shuttle flight in November 1994. The presence of large numbers of small ice crystals is inferred from the appearance of broad extinction features in the 8-12 micron region. These features were observed near the tropopause and at lower altitudes. Vertical profiles of the ice extinction (/km) in microwindows at 831, 957, and 1204/cm have been retrieved from the spectra and analyzed with a model for randomly oriented spheroidal ice crystals. An area-equivalent spherical radius of 6 microns is estimated from the smallest ice crystals observed in the 8-12 gm region. Direct penetration of clouds into the lower stratosphere is inferred from observations of cloud extinction extending from the upper troposphere to 50 mbar (20 km altitude). Cloud extinction between 3 and 5 microns shows very little wavelength dependence, at least for the cases observed by the ATMOS instrument in the tropics and subtropics during ATLAS 3.

We describe the updates to the spectroscopic parameters of ozone and its isotopes in the 1996 HITRAN compilation. Recent published studies not included in HITRAN are also summarized. Finally, we report the identification of infrared lines of the v(sub 3) bands of O-16O-16O-17 and O-16O-17O-16 in high-resolution solar spectra recorded by stratospheric balloon-borne and ground-based Fourier transform spectrometers.

Vertical mixing ratio profiles of four relatively long-lives gases, HCN, C2H2, CO, and C2H6, have been retrieved from 0.01/cm resolution infrared solar occultation spectra recorded between latitudes of 5.3degN and 31.4degN. The observations were obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Science (ATLAS) 3 shuttle flight, 3-12 November 1994. Elevated mixing ratios below the tropopause were measured for these gases during several of the occultations. The positive correlations obtained between the simultaneously measured mixing ratios suggest that the enhancements are likely the result of surface emissions, most likely biomass burning and/or urban industrial activities, followed by common injection via deep convective transport of the gases to the upper troposphere. The elevated levels of HCN may account for at least part of the "missing NO," in the upper troposphere. Comparisons of the observations with values measured during a recent aircraft campaign are presented.

Stratospheric measurements of H2O and CH4 by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer on the ATLAS-3 shuttle flight in November 1994 have been examined to investigate the altitude and geographic variability of H2O and the quantity H = (H2O + 2CH4) in the tropics and at mid-latitudes (8 to 49 deg N) in the northern hemisphere. The measurements indicate an average value of 7.24 plus or minus 0.44 ppmv for H between altitudes of about 18 to 35 km, corresponding to an annual average water vapor mixing ratio of 3.85 plus or minus 0.29 ppmv entering the stratosphere. The H2O vertical distribution in the tropics exhibits a wave-like structure in the 16- to 25-km altitude range, suggestive of seasonal variations in the water vapor transported from the troposphere to the stratosphere. The hygropause appears to be nearly coincident with the tropopause at the time of observations. This is consistent with the phase of the seasonal cycle of H2O in the lower stratosphere, since the ATMOS observations were made in November when the H2O content of air injected into the stratosphere from the troposphere is decreasing from its seasonal peak in July - August.

Measurements of the long-lived tracers CH4, N2O, and HF from the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument during the Atmospheric Laboratory for Science and Applications-2 (ATLAS-2) Space Shuttle mission in April 1993 are used to infer average winter descent rates ranging from 0.8 km/month at 20 km to 3.2 km/month at 40 km in the Arctic polar vortex during the 1992-93 winter. Descent rates in the mid-stratosphere are similar to those deduced for the Antarctic vortex using ATMOS/ATLAS-3 measurements in November 1994, but the shorter time period of descent in the Arctic leads to smaller total distances of descent. Strong horizontal gradients observed along the vortex edge indicate that the Arctic vortex remains a significant barrier to transport at least until mid-April in the lower to middle stratosphere.

The ATMOS Fourier transform spectrometer was flown for a fourth time on the Space Shuttle as part of the ATLAS-3 instrument payload in November 1994. More than 190 sunrise and sunset occultation events provided measurements of more than 30 atmospheric trace gases at latitudes 3 - 49 deg N and 65 - 72 deg S, including observations both inside and outside the Antarctic polar vortex. The instrument configuration, data retrieval methodology, and mission background are described to place in context analyses of ATMOS data presented in this issue.

We compare volume mixing ratio profiles of N2O, CFC-11, CFC-12, CCl4, SF6, and HCl in the mid-latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during Nov. 1994. Good agreement is found between ATMOS and in situ correlations of [CFC-11], [CFC-12], and [SF6] with [N2O]. ATMOS measurements of [CCl4] are 15% high compared to ER-2 data, but agree within the systematic uncertainties. ATMOS observations of [HCl] vs [N2O] are within approximately 10% of ER-2 data for [HCl] > 1 ppbv, but exceed in situ measurements by larger fractional amounts for smaller [HCl]. ATMOS measurements of [ClONO2] agree well with values inferred from in situ observations of [ClO], [NO], and [O3]. The sum of [HCl] and [ClONO2] observed by ATMOS, supplemented by a minor contribution from [ClO] estimated with a photochemical model, is consistent with the levels of inorganic chlorine inferred from in situ measurements of chlorine source gases.

We compare volume mixing ratio profiles of N2O, O3, NO(y), H2O, CH4, and CO in the mid-latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during Nov 1994. ATMOS and ER-2 observations of (N2O) show good agreement, as do measured correlations of (O3), (NO(y)), (H2O), and (CH4) with (N2O). Thus a consistent measure of the hydrogen (H2O, CH4) content of the lower stratosphere is provided by the two platforms. The similarity of (NO(y)) determined by detection of individual species by ATMOS and the total (NOy) measurement on the ER-2 provides strong corroboration for the accuracy of both techniques. A 25% discrepancy in lower stratospheric (CO) observed by ATMOS and the ER-2 remains unexplained. Otherwise, the agreement for measurements of long-lived tracers demonstrates the ability to combine ATMOS data with in situ observations for quantifying atmospheric transport.

Volume mixing ratio (VMR) profiles of OCS, HCN, SF6, and CHClF2 (HCFC-22) have been measured near 30 deg N latitude by the Atmospheric Trace Molecule Spectroscopy Fourier transform spectrometer during shuttle flights on 29 April - 6 May 1985 and 3-2 November 1994. The change in the concentration of each molecule in the lower stratosphere has been derived for this 9 1/2-year period by comparing measurements between potential temperatures of 395 to 800 K (approximately 17 to 30 km altitude) relative to simultaneously measured values of the long-lived tracer N2O. Exponential rates of increase inferred for 1985-to 1994 from these comparisons are (0.1 plus or minus 0.4)% yr(exp-1) for OCS, (1.0 plus or minus 1.0)% yr(exp-1) for HCN, (8.0 +/- 0.7)% yr(exp-1) for SF6, and (8.0 +/- 1.0)% yr(exp-1) for CHClF2 (HCFC-22), 1 sigma. The lack of an appreciable trend for OCS suggests the background (i.e. nonvolcanic) source of stratospheric aerosol was the same during the two periods. These results are compared with trends reported in the literature.

Stratospheric mixing ratios of CH3D from 100 mb to 17mb (approximately equals 15 to 28 km)and HDO from 100 mb to 10 mb (approximately equals 15 to 32 km) have been inferred from high resolution solar occultation infrared spectra from the Atmospheric Trace MOlecule Spectroscopy (ATMOS) Fourier-transform interferometer. The spectra, taken on board the Space Shuttle during the Spacelab 3 and ATLAS-1, -2, and -3 missions, extend in latitude from 70 deg S to 65 deg N. We find CH3D entering the stratosphere at an average mixing ratio of (9.9 +/- 0.8) x 10(exp -10) with a D/H ratio in methane (7.1 +/- 7.4)% less than that in Standard Mean Ocean Water (SMOW) (1 sigma combined precision and systematic error). In the mid to lower stratosphere, the average lifetime of CH3D is found to be (1.19 +/- 0.02) times that of CH4, resulting in an increasing D/H ratio in methane as air 'ages' and the methane mixing ratio decreases. We find an average of (1.0 +/- 0.1) molecules of stratospheric HDO are produced for each CH3D destroyed (1 sigma combined precision and systematic error), indicating that the rate of HDO production is approximately equal to the rate of CH3D destruction. Assuming negligible amounts of deuterium in species other than HDO, CH3D and HD, this limits the possible change in the stratospheric HD mixing ratio below about 10 mb to be +/- 0.1 molecules HD created per molecule CH3D destroyed.

We compare volume mixing ratio profiles of N2O, O3, NO(y) H2O, CH4, and CO in the mid-latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during Nov 1994. ATMOS and ER-2 observations of [N2O] show good agreement, as do measured correlations of [O3], [NO(y)], [H2O], and [CH4] with [N2O]. Thus a consistent measure of the hydrogen (H2O, CH4) content of the lower stratosphere is provided by the two platforms. The similarity of [NO(y)] determined by detection of individual species by ATMOS and the total [NO(y)] measurement on the ER-2 provides strong corroboration for the accuracy of both techniques. A 25% discrepancy in lower stratospheric [CO] observed by ATMOS and the ER-2 remains unexplained. Otherwise, the agreement for measurements of long-lived tracers demonstrates the ability to combine ATMOS data with in situ observations for quantifying atmospheric transport.

Simultaneous stratospheric volume mixing ratios (VMR's) measured inside and outside the Antarctic vortex by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument in November 1994 reveal previously unobserved features in the distributions of total reactive nitrogen (NO(y)) and total hydrogen (H2O + 2CH4). Maximum removal of NO(y) due to sedimentation of polar stratospheric clouds (PSC's) inside the vortex occurred at a potential temperature (Theta) of 500-525 K (approximately 20 km), where values were 5 times smaller than measurements outside. Maximum loss of H2O + 2CH4 due to PSC's occurred in the vortex at 425-450 K, approximately 3 km lower than the peak NO(y) loss. At that level, H2O + 2CH4 VMR's inside the vortex were approximately 70% of corresponding values outside. The Antarctic and April 1993 Arctic measurements by ATMOS show no significant differences in H2O + 2CH4 VMR's outside the vortices in the two hemispheres. Elevated NO(y) VMRs were measured inside the vortex near 700 K. Recent model calculations indicate that this feature results from downward transport of elevated NO(y) produced in the thermosphere and mesosphere.

Observations of the long-lived tracers N2O, CH4 and HF obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument in early November 1994 are used to estimate average descent rates during winter in the Antarctic polar vortex of 0.5 to 1.5 km/month in the lower stratosphere, and 2.5 to 3.5 km/month in the middle and upper stratosphere. Descent rates inferred from ATMOS tracer observations agree well with theoretical estimates obtained using radiative heating calculations. Air of mesospheric origin (N2O less than 5 ppbV) was observed at altitudes above about 25 km within the vortex. Strong horizontal gradients of tracer mixing ratios, the presence of mesospheric air in the vortex in early spring, and the variation with altitude of inferred descent rates indicate that the Antarctic vortex is highly isolated from midlatitudes throughout the winter from approximately 20 km to the stratopause. The 1994 Antarctic vortex remained well isolated between 20 and 30 km through at least mid-November.

Vertical enrichment profiles of stratospheric O-16O-16O-18 and O-16O-18O-16 (hereafter referred to as (668)O3 and (686)O3 respectively) have been derived from space-based solar occultation spectra recorded at 0.01 cm(exp-1) resolution by the ATMOS (Atmospheric Trace MOlecule Spectroscopy) Fourier transform infrared (FTIR) spectrometer. The observations, made during the Spacelab 3 and ATLAS-1, -2, and -3 shuttle missions, cover polar, mid-latitude and tropical regions between 26 to 2.6 mb inclusive (approximately 25 to 41 km). Average enrichments, weighted by molecular (48)O3 density, of (15 +/- 6)% were found for (668)O3 and (10 +/- 7)% for (686)O3. Defining the mixing ratio of (50)O3 as the sum of those for (668)O3 and (686)O3, an enrichment of (13 plus or minus 5)% was found for (50)O3 (1 sigma standard deviation). No latitudinal or vertical gradients were found outside this standard deviation. From a series of ground-based measurements by the ATMOS instrument at Table Mountain, California (34.4 deg N), an average total column (668)O3 enrichment of (17 +/- 4)% (1 sigma standard deviation) was determined, with no significant seasonal variation discernable. Possible biases in the spectral intensities that affect the determination of absolute enrichments are discussed.

Stratospheric volume mixing ratio profiles of carbon tetrafluoride, CF4, obtained with the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument during the ATLAS (Atmospheric Laboratory for Applications and Science) -3 mission of 1994 are reported. Overall the profiles are nearly constant over the altitude range 20 to 50 km, indicative of the very long lifetime of CF4 in the atmosphere. In comparison to the stratospheric values of CF4 inferred from the ATMOS/Spacelab 3 mission of 1985, the 1994 concentrations are consistent with an exponential increase of (1.6 +/- 0.6)% yr(exp -1). This increase is discussed with regard to previous results and likely sources of CF4 at the ground. Further, it is shown that simultaneous measurements of N2O and CF4 provide a means of constraining the lower limit of the atmospheric lifetime of CF4 at least 2,300 years, two sigma.

Using results from a time-dependent photochemical model to calculate the diurnal variation of NO and NO2, we have corrected Atmospheric Trace MOlecule Spectroscopy (ATMOS) solar-occultation retrievals of the NO and NO2 abundances at 90' solar zenith angle. Neglecting to adjust for the rapid variation of these gases across the terminator results in potential errors in retrieved profiles of approximately 20% for NO2 and greater than 100% for NC at altitudes below 25 km. Sensitivity analysis indicates that knowledge of the local 03 and temperature profiles, rather than zonal mean or climatological conditions of these quantities, is required to obtain reliable retrievals of NO and NO2 in the lower stratosphere. Extremely inaccurate 03 or temperature values at 20 km can result in 50% errors in retrieved NO or NO2. Mixing ratios of NO in the mid-latitude, lower stratosphere measured by ATMOS during the November 1994 ATLAS-3 mission compare favorably with in situ ER-2 observations, providing strong corroboration of the reliability of the adjusted space-borne measurements.

Partitioning between HCl and ClONO2 and among the main components of the reactive nitrogen family (NO, NO2, HNO3, ClONO2, N2O5, and HO2NO2) has been studied inside and outside the Antarctic stratospheric vortex based on ATMOS profiles measured at sunrise during the 3-12 November 1994 ATLAS-3 Shuttle mission. Elevated mixing ratios of HCl in the lower stratosphere with a peak of approximately 2.9 ppbv (10(exp -9) parts per volume) were measured inside the vortex near 500 K potential temperature (approximately 19 km). Maximum ClONO2 mixing ratios of approximately 1.2, approximately 1.4, and approximately 0.9 ppbv near 700 K (approximately 25 km) were measured inside, at the edge, and outside the vortex, respectively. Model calculations reproduce the higher levels of HCl and NO(x) (NO + NO2) inside the lower stratospheric vortex both driven by photochemical processes initiated by low O3. The high HCl at low O3 results from chemical production of HC1 via the reaction of enhanced Cl with CH4, limited production of ClONO2, and the descent of inorganic chlorine from higher altitudes.

The Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument is a high resolution Fourier transform spectrometer that measures atmospheric composition from low Earth orbit with infrared solar occultation sounding in the limb geometry. Following an initial flight in 1985, ATMOS participated in the Atmospheric Laboratory for Applications and Science (ATLAS) 1, 2, and 3 Space Shuttle missions in 1992, 1993, and 1994 yielding a total of 440 occultation measurements over a nine year period. The suite of more than thirty atmospheric trace gases profiled includes CO2, O3, N2O, CH4, H2O, NO, NO2, HNO3, HCl, HF, ClONO2, CCl3F, CCl2F2, CHF2Cl, and N2O5. The analysis method has been revised throughout the mission years culminating in the 'version 2' data set. The spectroscopic error analysis is described in the context of supporting the precision estimates reported with the profiles; in addition, systematic uncertainties assessed from the quality of the spectroscopic database are described and tabulated for comparisons with other experiments.

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.

UNKNOWN

Covers chlorine measurements in atmosphere, refer to abstract.

UNKNOWN

We have compared volume mixing ration profiles of N2 O, CFC-11, CFC-12, CCI4 , SF6, and HCI measured for the mid-latitude stratosphere by the ATMOS Fourier transform spectrometer during the ATLAS-3 Space Shuttle mission of NOvember 1994 with in situ measurements acquired aboard the NASA ER-2 aircraft during the same time period.

We compare the mixing rations of N2O, CFC-11, CFC-12, CCI4, SF6, and HCI in the mid-latitude stratosphere measured by the ATMOS Fourier transform spectrometer with in situ measurements acquired aboard the NASA ER-2 aircraft during November 1994. Good agreement is found between ATMOS and in situ correlations of CFC-11, CFC-12, and SF6 with N2O. ATMOS observations of CCI4 are approx. 15 percent higher than the ER-2 data, but within the systematic uncertainties.

Stratospheric measurements of H(sub 2)O and CH(sub 4) by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer on the ATLAS-3 Shuttle flight in November 1994 have been used to investigate the altitude and geographic variability of H(sub 2)O and the quantity H(Eta?) = (H(sub 2)O + CH(sub 4)) in the tropics and at mid-latitudes (8-49in the northern hemisphere.

Using results from a time-dependent photochemical model to calculate the diurnal variation of NO and NO(sub 2), we have corrected Atmospheric Trace Molecule Spectroscopy (ATMOS) solar-occultation retrievals of the NO and NO(sub 2) abundances at 90 solar zenith angle. Neglecting to adjust for the rapid variation of these gases across the terminator results in potential errors in retrieved profiles of approx. 20 percent for NO(sub 2) and greater than 100 percent for NO at altitudes below 25 KM.

The ATMOS Fourier transform spectrometer was flown for a fourth time on the Space Shuttle as part of the ATLAS-3 instrument payload in November 1994. More than 190 sunrise and sunset occultation events provided measurements of more than 30 atmospheric trace gases at latitudes 3-49N and 65-72S, including observations both inside and outside the Antarctic polar vortex.

Descent rates for atmospheric inferred from ATMOS (Atmospheric Trace Molecule Spectroscopy)tracer observations agree well with theoretical estimates obtained using radiative heating calculations...