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Measuring CO2 using a ground-based FTIR spectrometer

In 2013, the globally averaged concentration of carbon dioxide (CO2) has reached 396 ppm from its pre-industrial concentration of 280 ppm.  The majority of scientists agree that anthropogenic CO2 is the major cause of global warming. As the environment changes (due to global warming) so will the ability of the biosphere to store CO2, thus affecting the amount present in the atmosphere.  Traditionally, CO2 has been monitored by very precise flask measurements taken at sampling stations that are sparsely located. Space based remote sensing satellites (like GOSAT and eventually OCO2) measure the global distribution of CO2 in order to determine how the sources and sinks of CO2 vary with time and location.
The Total Carbon Column Observing Network (TCCON) is a ground-based network of Fourier transform infrared (FTIR) spectrometers that measure precise and accurate columns of CO2. The goal of the network is to validate satellite measurements of CO2. In order to accomplish this, solar spectra is recorded at high resolution. Spectral fits of solar spectra show systematic residuals because the Voigt profile does not adequately describe the molecular line shape of CO2.  In this talk I will show that the speed-dependent Voigt with line mixing adequately describe the molecular line shape of CO2. I will show that this line shape greatly improves the spectral fits of both laboratory and solar spectra, as well as improves the airmass-dependence of CO2 measurements at TCCON sites.