Investigating Carbon Monoxide in the Stratosphere using Infrared Spectroscopy

We analyzed CO measurements in the upper troposphere and lower stratosphere via infrared spectroscopy using a Fourier Transform Infrared (FTIR) spectrometer that was flown aboard two aircraft, a NASA DC8 and NCAR Sabreliner. Measurements were made between 1978-1992. Measurements of stratospheric CO can aid in understanding transport in the lower stratosphere. Calculated reference spectra were generated to analyze the observed spectra produced by the spectrometer using standard temperature and mixing ratio profiles and molecular line parameters. Nonlinear least squares fitting were used to match calculated reference spectra with observed spectra. The CO amount in the best-fit reference spectrum was assigned to the observed spectrum. CO column was corrected to be the amount above the 200mb pressure surface because column varies rapidly with aircraft altitude. CO column was plotted against latitude and then divided into seasons to observe any seasonal variations. Higher columns occurred near the equator while lower columns occurred near the poles. This characteristic was consistent in the seasonal plots, indicating little seasonal variations. Higher CO column near the equator is explained by presence of tropospheric air that has a higher density of CO and CO entering the stratosphere at the equator. Lower CO column near the poles is due to presence of only stratospheric air that has less CO. The observed column was similar in both hemispheres near the poles, where the observation is wholly stratospheric, but asymmetric about 20 because of the large interhemispheric gradient in tropospheric CO.