D. G. Murcray

Atmospheric sulfur hexafluoride: Sources, sinks and greenhouse warming

Model calculations using estimated reaction rates of sulfur hexafluoride (SF6) with OH and O(1D) indicate that the atmospheric lifetime due to these processes may be very long (25,000 years). An upper limit for the UV cross section would suggest a photolysis lifetime much longer than 1000 years. The possibility of other removal mechanisms are discussed. The estimated lifetimes are consistent with other estimated values based on recent laboratory measurements. There appears to be no known natural source of SF6. An estimate of the current production rate of SF6 is about 5 kt/yr. Based on historical emission rates, we calculated a present-day atmospheric concentrations for SF6 of about 2.5 parts per trillion by volume (pptv) and compared the results with available atmospheric measurements. It is difficult to estimate the atmospheric lifetime of SF6 based on mass balance of the emission rate and observed abundance. There are large uncertainties concerning what portion of the SF6 is released to the atmosphere. Even if the emission rate were precisely known, it would be difficult to distinguish among lifetimes longer than 100 years since the current abundance of SF6 is due to emission in the past three decades. More information on the measured trends over the past decade and observed vertical and latitudinal distributions of SF6 in the lower stratosphere will help to narrow the uncertainty in the lifetime. Based on laboratory-measured IR absorption cross section for SF6, we showed that SF6 is about 3 times more effective as a greenhouse gas compared to CFC 11 on a per molecule basis. However, its effect on atmospheric warming will be minimal because of its very small concentration. We estimated the future concentration of SF6 at 2010 to be 8 and 10 pptv based on two projected emission scenarios. The corresponding equilibrium warming of 0.0035°C and 0.0043°C is to be compared with the estimated warming due to CO2 increase of about 0.8°C in the same period.

Measurements of stratospheric halocarbon distributions using infrared techniques

Absorption bands of CF2Cl2, CFCl3 and CCl4 have been observed in infrared sunset solar spectra in the 800-1000 cm−1 region from 30 km altitude during a balloon flight made in September 1975. The infrared absorption bands were used to derive the distribution of these constituents in the upper troposphere and lower stratosphere. The results are compared with 1968 data and with current results of other authors.

Presence of HNO 3 in the Upper Atmosphere

Observations of absorption of solar radiation by atmospheric nitric acid obtained on different balloon flights are presented. This absorption occurs in three different wavelength intervals. The use of the very long paths, occurring near sunset, for enhancing weak absorption is discussed.

Stratospheric N 2 O mixing ratio profile from high-resolution balloon-borne solar absorption spectra and laboratory spectra near 1880 cm −1

A nonlinear least-squares fitting procedure has been used to derive the stratospheric N(2)O mixing ratio profile from balloon-borne solar absorption spectra and laboratory spectra near 1880 cm(-1). The atmospheric spectra were recorded during sunset from a float altitude of 33 km with the University of Denver 0.02-cm(-1) resolution interferometer near Alamogordo, N.M. (33 degrees N), on 10 Oct. 1979. The laboratory data were used to determine the N(2)O line intensities. The measurements indicate an N(2)O mixing ratio of 264 ppbv near 15 km decreasing to 155 ppbv near 28 km.

Variation of the Infrared Solar Spectrum Between 700 cm −1 and 2240 cm −1 with Altitude

A grating spectrometer with a Ge: Cu detector was flown on three balloon flights. Spectra in the 4-14.3-micro region were obtained at various altitudes from the ground through 30 km with a resolution considerably better than that achieved in previous flights. Some of the spectra were obtained over long paths at float altitude, during the sunset. Data from these flights are presented with a discussion of the significant features of the observed absorptions. Special emphasis is put on the new features observed during the sunset.

Spectral least squares quantification of several atmospheric gases from high resolution infrared solar spectra obtained at the South Pole

Abstract Spectral least squares fitting has been used to analyze high resolution (0.02 cm -1 ) i.r. solar spectra obtained at the South Pole in 1980. The spectral regions analyzed allow the simultaneous quantification of CO 2 , H 2 O, N 2 O, CH 4 , and O 3 . Information is obtained on the column amount and on the vertical distribution.

Mt. Pinatubo SO2 Column Measurements From Mauna Loa

Absorption features of the v1 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) × 1016 molecules cm−2 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 × 1016 molecules cm−2 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.

Distribution of Nitric Acid Vapor in the Stratosphere as Determined from Infrared Atmospheric Emission Data

Abstract Infrared emission spectra were measured in the stratosphere at various altitudes and from various zenith angles by means of a balloon-borne Czerny-Turner spectrometer. The equation of radiative transfer was applied to the radiances measured at 11.2μ to yield a concentration profile of HNO3 vapor. The resulting HNO3 concentration profile was characterized by a negligible concentration below 14 km, a maximum concentration of ∼(1.5±0.5)×1010 molecules cm−3 at ∼(19±5) km, and a diminishing concentration above these altitudes.

High-resolution infrared atmospheric spectra of ozone in the 10-μm region: Analysis of ν1 and ν3 bands-assignment of the (ν1 + ν2) − ν2 band

Abstract 1988 lines of ozone have been observed in the atmospheric spectrum in the region 1060 to 1220 cm −1 , 1394 of them have been assigned to the ν 1 band, and 480 to the ν 3 , particularly corresponding to Δ K −1 = 2. The analysis has been performed using the Watson Hamiltonian, taking account of the strong Coriolis coupling between the 001 and 100 levels. The constants for the latter two states, the spectra and a listing of the observed and calculated wave-numbers, with their assignment, are given. In addition, 114 lines of the “hot” band ( ν 1 + ν 2 ) − ν 2 have been observed and assigned and are reported.

Distribution of Water Vapor in the Stratosphere as Determined from Balloon Measurements of Atmospheric Emission Spectra in the 24–29-μm Region

The stratospheric water vapor mixing ratio altitude profile has been derived from spectral observations of the downward night emission from the pure rotation water vapor lines in the 24-29-microm region of the spectrum. The data were obtained during two balloon flights, made on 22 February 1971 and on 29 June 1971, using a balloon-borne spectral radiometer with ~2 cm(-1) resolution. The observed radiances have been fitted to line-by-line, layer-by-layer radiance calculations, from which the water vapor mixing ratio between 10 km and 30 km has been flights show a broad minimum around of 6 x 10(-7)g/g to 4 x 10(-6) g/g.