Infrared measurements of atmospheric gases above Mauna Loa, Hawaii, in February 1987

Abstract

Infrared solar absorption spectra recorded at 0.02 cm−1 resolution from the National Oceanic and Atmospheric Administration (NOAA) Geophysical Monitoring for Climate Change (GMCC) program station at Mauna Loa, Hawaii (latitude 19.5°N, longitude 155.6°W, elevation 3.40 km), in February 1987 have been analyzed to determine simultaneous total vertical column amounts for 13 atmospheric gases. Average tropospheric concentrations of CO2, N2O, CH4, and CHClF2 and the daytime diurnal variations of the total columns of NO and NO2 have also been inferred. The retrieved total columns (in molecules cm−2) of the nondiurnally varying gases are 1.6±0.2×1015 for HCl, 5.9±1.2 ×1015 for HNO3, 2.0±0.2×1021 for H216O, 4.4±0.7×1018 for H218O, 2.7±0.1×1017 for HDO, 2.3±0.2×1019 for CH4, 5.0±0.5×1021 for CO2, 6.7±0.8×1018 for O3, 4.3±0.4×1018 for N2O, 1.0±0.2×1016 for C2H6, and 9.7±2.5×1014 for CHClF2. We compare the total column measurements of HCl and HNO3 with previously reported ground‐based, aircraft, and satellite measurements. The results for HCl are of particular interest because of the expected temporal increase in the concentration of this gas in the stratosphere. However, systematic differences among stratospheric HCl total column measurements from 1978 to 1980 and the absence of observations of free tropospheric HCl above Mauna Loa make it impossible to obtain a reliable estimate of the trend in the total burden of HCl. The measured HNO3 total column is consistent with aircraft measurements from ∼12 km altitude. The O3 total column deduced from the IR spectra agrees with correlative Mauna Loa Umkehr measurements within the estimated error limits. The column‐averaged D/H ratio of water vapor is (68±9)×10−6, which is 0.44±0.06 times the reference value of 155.76×10−6 for standard mean ocean water (SMOW). This large depletion in the D content of water vapor is similar to published measurements of the upper troposphere and lower stratosphere. Average tropospheric concentrations deduced for CO2, N2O, and CH4 are in good agreement with correlative NOAA GMCC surface data, indicating consistency between the measurement techniques for determining tropospheric volume mixing ratios. Results of the present study indicate that Mauna Loa is a favorable site for infrared monitoring of atmospheric gases. The site is particularly favorable for monitoring the tropospheric volume mixing ratios of long‐lived gases, since the high altitude of the tropopause reduces corrections required to account for the decrease in volume mixing ratio in the stratosphere.