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Solar absorption spectra were recorded for the first time in 5 years with the McMath Fourier transform spectrometer at the US National solar Observatory on Kitt Peak in southern Arizona, USA (31.91 N latitude, 111.61 W longitude, 2.09 km altitude). The solar absorption spectra cover 750-1300 and 1850-5000 cm(sup -1) and were recorded on 20 days during March-June 2009. The measurements mark the continuation of a long-term record of atmospheric chemical composition measurements that have been used to quantify seasonal cycles and long-term trends of both tropospheric and stratospheric species from observations that began i 1977. Fits to the measured spectra have been performed, and they indicate the spectra obtained since return to operational status are nearly free of channeling and the instrument line shape function is well reproduced taking into account the measurement parameters. We report updated time series measurements of total columns for six atmospheric species and their analysis for seasonal cycles and long-term trends. An sn example, the time series fit shows a decrease in the annual increase rate i Montreal-Protocol-regulated chlorofluorocarbon CCL2F2 from 1.51 plus or minus 0.38% yr(sup -1) at the beginning of the time span to -1.54 plus or minus 1.28 yr(sup -1) at the end of the time span, 1 sigma, and hence provides evidence for the impact of those regulations on the trend.

Long-term trend and seasonal variation of the mean free tropospheric volume mixing ratios of carbon monoxide (CO) and hydrogen cyanide (HCN) have been derived from analysis of a time series of solar absorption spectra recorded from the US National Solar Observatory on Kitt Peak (31.9°N, 111.6°W, 2.09 km altitude) spanning almost three decades. The results of a fit to the CO 258 daily averages from May 1977 to April 2005 as a function of time with a model that assumes a sinusoidal seasonal cycle and a linear long-term trend with time yield a mean volume mixing ratio of 102 ± 3 ) parts per billion ( 10 - 9 per unit volume) below 10 km altitude, 1 sigma. The CO measurements show a seasonal cycle with a maximum in March and a minimum in September with an amplitude of ( 22.3 ± 1.5 ) % relative to the mean. The best-fit corresponds to a long-term CO trend of ( 0.15 ± 0.14 ) % yr - 1 , 1 sigma, relative to the mean. To quantify the possible impact of periods of intense fires, the CO measurements have been compared with the measurements of HCN, a well-documented emission product of biomass burning with a lifetime of ∼ 5 months. The best fit to the full HCN time series of 208 daily averages from May 1978 to April 2005 results in a mean volume mixing ratio of ( 0.219 ± 0.007 ) ppbv below 10 km altitude with a similar seasonal cycle, though with a lower relative amplitude than for CO. Although same-day enhancements up to a factor of 1.87 for HCN and 1.24 for CO were measured relative to values predicted by a fit to the time series that accounts for the seasonal cycles and trends of both molecules, excluding time periods of elevated fire emissions has no significant impact on the best-fit long-term free tropospheric CO and HCN trends. Our result of no long-term CO trend since the late 1970s suggests that the global average long-term decline reported from 1990 through 1995 measurements has not continued in the free troposphere. Similarly, a fit to the full time series of 208 HCN free tropospheric daily averages with the same model yields an average 2.09–10 km mixing ratio of 0.219 ppbv and a long-term trend of ( - 0.12 ± 0.14 ) % yr - 1 , 1 sigma, relative to the mean since 1978, also indicating no significant long-term trend above the lower mid-latitude continental US Kitt Peak station. The results for both molecules suggest the site was not significantly impacted by summer boreal fires during the time span of the measurements that in some years cause widespread pollution above northern higher latitude sites.

An empirical line-by-line model for the infrared solar transmittance spectrum is presented. The model can be incorporated into radiative transfer codes to allow fast calculation of all relevant emission and absorption features in the solar spectrum in the mid-infrared region from 700 to 5000 cm - 1 . The transmittance is modelled as a function of the diameter of the field-of-view centered on the solar disk: the line broadening due to solar rotation as well as center-to-limb variations in strength and width are taken into account for stronger lines. Applications of the model presented here are in the fields of terrestrial remote sensing in the mid-infrared spectral region when the sun is used as radiation source or scattered solar radiation contributes to the measured signal and in the fields of atmospheric radiative transfer algorithms which compute the propagation of infrared solar radiation in the terrestrial atmosphere.

We report average tropospheric CH 4 volume mixing ratios retrieved from a 27 year time series of high spectral resolution infrared solar absorption measurements recorded between May 1977 and July 2004 at the US National Solar Observatory station on Kitt Peak ( 31 . 9 ∘ N , 111 . 6 ∘ W , 2.09 km altitude) and their comparison with surface in situ sampling measurements recorded between 1983 and 2004 at the Climate Monitoring and Diagnostics Laboratory (CMDL) station at Niwot Ridge, Colorado ( 40 . 0 ∘ N , 105 . 5 ∘ W , 3013 m altitude). The two measurement sets therefore overlap for the 1983–2004 time period. An average tropospheric volume mixing ratios of 1814 ± 48 ppbv ( 1 ppbv = 10 - 9 per unit volume) has been derived from the solar absorption time series with a best-fit increase rate trend equal to 8.26 ± 2.20 ppbv yr - 1 in 1983 decreasing to 1.94 ± 3.69 ppbv yr - 1 in 2003. The CMDL measurements also show a continuous long-term CH 4 volume mixing ratio rise, with subsequent slowing down. A mean ratio of the retrieved average tropospheric volume mixing ratio to the CMDL volume mixing ratio for the overlapping time period of 1.038 ± 0.034 indicates agreement between both data sets within the quantified experimental errors.

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.

The average tropospheric volume mixing ratios of chlorofluorocarbon 12 (CCl2F2) have been retrieved from high-spectral resolution ground-based infrared solar-absorption spectra recorded from March 1982 to October 2003 with the McMath Fourier transform spectrometer at the US National Solar Observatory facility on Kitt Peak in southern Arizona (31.9°N, 111.6°W, 2.09 km altitude). The retrievals are based on fits to the unresolved ν 8 band Q-branches near 922 cm - 1 using the SFIT2 retrieval algorithm. The annual increase rate was equal to ( 16.88 ± 1.37 ) parts per trillion ( 10 - 12 ) by volume at the beginning of the time series, March 1982, or ( 4.77 ± 0.04 ) % , 1 sigma, declining progressively to ( 2.49 ± 1.24 ) parts per trillion, by volume at the end, October 2003, or ( 0.46 ± 0.24 ) % , 1 sigma. Average tropospheric mixing ratios from the solar spectra have been compared with average surface flask and in situ sampling measurements from the Climate Monitoring and Diagnostics Laboratory (CMDL) station at Niwot Ridge, CO, (USA) (40.0°N, 105.5°W, 3013 m altitude). The average ratio and standard deviation of the monthly means of the retrieved tropospheric mixing ratios relative to the CMDL surface mixing ratios is ( 1.01 ± 0.03 ) for the overlapping time period. Both datasets demonstrate the progressive impact of the Montreal protocol and its strengthening amendments on the trend of CCl2F2, though a tropospheric decrease has yet to be observed.

A rigorous and systematic intercomparison of codes used for the retrieval of trace gas profiles from high-resolution ground-based solar absorption FTIR measurements is presented for the first time. Spectra were analyzed with the two widely used independent, retrieval codes: SFIT2 and PROFFIT9. Vertical profiles of O 3 , HNO 3 , HDO, and N 2 O were derived from the same set of typical observed spectra. Analysis of O 3 was improved by using updated line parameters. It is shown that profiles and total column amounts are in excellent agreement, when similar constraints are applied, and that the resolution kernel matrices are also consistent. Owing to the limited altitude resolution of ground-based observations, the impact of the constraints on the solution is not negligible. It is shown that the results are also compatible for independently chosen constraints. Perspectives for refined constraints are discussed. It can be concluded that the error budget introduced by the radiative transfer code and the retrieval algorithm on total columns deduced from high-resolution ground-based solar FTIR spectra is below 1%.

Recent work on new line parameters for the X 1 Σ + (0–0),(0–1) H 79 Br, H 81 Br bands and the X 1 Σ + (0–0), (0–1) HI bands, which include hyperfine structure components, has been extended for an update of spectroscopic databases in use for atmospheric spectroscopy. The updated line parameters, now incorporated in HITRAN 2001, are discussed in comparison to HITRAN 1996.

Isotopic ozone lines of 16O16O17O and 16O17O16O in the 5 μm region are identified for the first time in balloon-borne high-resolution (0.003 cm −1 ) solar absorption spectra. A few of these lines also are observed in ground-based spectra. These lines need to be included in analysis of atmospheric absorption spectra, in addition to the recently identified 16 O 16 O 18 O , 16 O 18 O 16 O and 16O12C34S lines in this region.

Isotopic lines of carbonyl sulfide, 16O12C34S in the ν3 region (band center 2061.446 cm −1 ) are identified for the first time in balloon-borne and ground-based high-resolution ( 0.003 cm −1 ) solar absorption spectra. A quantitative analysis of the balloon-borne data is reported. The isotopic abundance may reveal the origins of the carbonyl sulfide in the atmosphere.

Improved line parameters are generated for the HBr (0–1) fundamental band. These new parameters, which include hyperfine structure, allow fitting of HBr absorption features from gas cells used for long-term validation of infrared high-resolution spectrometers.

Hyperfine lines associated with the X 1 Σ + (0–0) and (0–1) bands of H 127 I are generated. Discussion of the HI line parameters in the HITRAN and SAO databases is presented. The new (0–0) line parameters are based on previously published far-infrared constants. High-resolution laboratory spectra in the infrared fundamental band region are presented and analyzed for new fine structure spectroscopic constants, which are combined with available hyperfine structure constants for calculating the new (0–1) line parameters.