Infrared measurements of atmospheric ethane (C₂H₆) from aircraft and ground‐based solar absorption spectra in the 3000 cm⁻¹ region

Abstract

A number of prominent Q‐branches of the ν7 band of C2H6 have been identified near 3000 cm−1 in aircraft and ground‐based infrared solar absorption spectra. The aircraft spectra provide the column amount above 12 km at various altitudes. The column amount is strongly correlated with tropopause height and can be described by a constant mixing ratio of 0.46 ppbv in the upper troposphere and a mixing ratio scale height of 3.9 km above the tropopause. The ground‐based spectra yield a column of 9.0 × 1015 molecules cm−2 above 2.1 km; combining these results implies a tropospheric mixing ratio of approximately 0.63 ppbv.

Seasonal cycle and secular trend of the total and tropospheric column abundance of ethane above the Jungfraujoch

“…Considering the fact that both the in situ and the airborne remote data do not have the degree of averaging of the ISSJ data and thus are still subject to natural variance, the agreement between the various data sets is reasonable. The only exception seems to be the measurement of 0.63 ppb by Coffey et al [ 1985], which appears to fall outside of the range of natural fluctuations allowed by Figure 6. The in situ European data (locations 2, 4, 7, and 8) average to 1.65 _+ 0.3 ppb, in good agreement with the ISSJ mean free troposphere value of 1.53 __+ 0.14 ppb derived using the modified vertical C2H 6 profile.…”

Concentrations of ethane (C2H6) in the lower stratosphere and upper troposphere and acetylene (C2H2) in the upper troposphere deduced from atmospheric trace molecule spectroscopy/Spacelab 3 spectra

“…Broadband laboratory spectra of C2H6 indicate that the strongest infrared absorption by this molecule occurs near 3000 cm-• where two parallel bands, the Fermi diad of v5 and v8 + v•, and the perpendicular v7 band, overlap [Smith, 1949;Nyquist et al, 1957]. The most prominent features in this region at moderate to high resolution [Cole et al, 1969[Cole et al, , 1980Murcray and Goldman, 1981;Pine and Lafferty, 1982] are the sharp v7 band Q branches, which have been identified recently as prominent absorbers in both high-resolution aircraft-borne and ground-based solar absorption spectra [Coffey et al, 1985]. Moderately strong absorptions by C2H6 also occur in the region of the v9 fundamental near 822 cm-• [Daunt et al, 1981;Henry et al, 1983;Atakan et al, 1983;Daunt et al, 1984;Murcray et al, 1984] and in the region of the overlapping v•2 + v4, rs, and v6 bands near 1500 cm -• [Susskind, 1974].…”

“…Quantitative analyses of atmospheric absorption using the v9 band Q branches (mostly •Q0 at 822.32 cm -•) were reported from high-resolution ground-based solar spectra [Zander et al, 1982] and from high-resolution balloon-borne and aircraft solar spectra . The v9 band Q branch features are about an order of magnitude weaker than the v7 band Q branches [Coffey et al, 1985] and hence are less sensitive for measuring trace amounts of atmospheric C2H6, but the v9 band absorptions are still useful for monitoring C2H6 at higher concentration levels. Coffey et al [1985] have been observed in the ATMOS spectra.…”

“…The v9 band Q branch features are about an order of magnitude weaker than the v7 band Q branches [Coffey et al, 1985] and hence are less sensitive for measuring trace amounts of atmospheric C2H6, but the v9 band absorptions are still useful for monitoring C2H6 at higher concentration levels. Coffey et al [1985] have been observed in the ATMOS spectra. For the present work we selected the PQ3 subbranch near 2976.8 cm -• for atmospheric quantification, as recommended by Coffey et al [1985].…”

The production of carbon monoxide by the homogeneous NO x -induced photooxidation of volatile organic compounds in the troposphere

“…This alkane is likely to have a constant mixing ratio with altitude in the tropopanse (Coffey et al, 1985;Blake and Rowland, 1986).…”