ABSORPTION COEFFICIENT OF CO2 AND FIRST-ORDER APPROXIMATION OF RADIATIVE FORCING

The CO2 is one of the two primary GHG and the source of carbon needed for photosynthesis and life on Earth. The spectral absorption coefficient alpha(lambda) [m(-1)] is a fundamental property of CO2 . It is required for modelling heat transfer at high temperature in furnaces, heat engines, wildfire, etc. and in the atmosphere at similar to 300 K. Using a FTIR spectrometer, infrared absorbance A(lambda) spectra of CO2 were measured with 0.5 cm(-1) resolution. All measurements were conducted at 295 K. The spectra cover the wavelength range 2 mu m < lambda < 18.2 mu m and the pressure range 0.04 atm < p < 3 atm. The spectra were used to determine the spectral absorption coefficient alpha(lambda) in the bands adjacent to the peaks 2.7 um, 4.26 um, and 15 um. The spectra of CO2 in air are also presented. A first-order approximation-model of the radiative forcing, Delta q, is presented. The FTIR spectra confirm that 400 ppm of CO2 is sufficient to saturate absorption in the central PQR region of the 15 um band. Consequently, radiative forcing is controlled by the wings (edge) regions of the 15 mu m band. The 100% increase in CO2 concentration will cause radiative forcing, Delta q(400ppmto800ppm) = 2.79 W/m(2), and temperature increase Delta T similar to 0.7 K. Tenfold (1000%) increase in CO2 concentration will increase radiative forcing by similar to 1.8x, so that Delta q4(00ppm to 4000ppm) = 5.03 W/m(2) and Delta T similar to 1.2 K.