Infrared spectroscopic measurements of the total column abundance of ethane (C2H6) above Lauder, New Zealand

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Abstract
Total vertical column abundances of atmospheric ethane (C2H6) have been retrieved from more than 350 high‐resolution infrared solar spectra recorded on 129 days between December 1992 and March 1994 at the Network for the Detection of Stratospheric Change (NDSC) station in Lauder, New Zealand (latitude 45.04°S, 169.68°E, 0.37 km altitude). The results are based on nonlinear least squares fits to narrow spectral intervals containing the unresolved C2H6 v7 band pQ3 and RQ0 subbranches at 2976.8 and 2986.7 cm−1, respectively. The measured Lauder column abundances show a pronounced seasonal cycle with a maximum value of (8.6±1.1) × 1015 molecules cm−2 in September and a minimum value of (3.8±0.5) × 1015 molecules cm−2 in February. Assuming a realistic vertical distribution for C2H6, these values correspond to surface level volume‐mixing ratios of 0.52 and 0.23 ppbv (parts per billion by volume), respectively. The phase and relative amplitude of the Lauder C2H6 seasonal cycle are similar to corresponding values determined from infrared measurements at the Jungfraujoch (46.55°N, 7.98°E, 3.58 km altitude) and Mauna Loa (latitude 19.5°N, longitude 155.6°W, 3.5 km altitude) NDSC stations, but the inferred absolute magnitudes of the Lauder surface level mixing ratios during the same season are significantly lower. The Lauder C2H6 measurements are also compared with published southern hemisphere surface level sampling measurements and two‐dimensional model calculations.