A method for estimating total content of a component of a gas mixture having inhomogeneous temperature and concentration distribution is proposed. The approach assumes selection of a spectral region with minimum temperature dependence of the absolute absorption coefficient. Variation of the shape and width of the spectrometer's instrumental function allowed us to reveal optimal parameters providing for the smallest error in determination of the gas concentration from transmission measurements. Measurements of carbon monoxide have been numerically simulated, and it has been shown that in a practically important case (temperature distribution of a forest fire) the error in concentration restoration does not exceed 10%