Benzene and substituted benzenes have unique spectral characteristics that allow the compounds to be identified and quantified even in complex mixtures. Each spectrum in this group has sharp spectral features, "spikes", at particular frequencies. High spectral resolution assists in the utilization of these features. For benzene measurement, the narrow feature near 674 wavenumbers should be chosen, because it is about 70 times taller than the next tallest feature in the spectrum. Unfortunately, in atmospheric measurements carbon dioxide absorption is found to overlay this strongest benzene feature. However, if the optical path in air is 80 meters or less, there is enough infrared transmission to allow benzene to be measured, providing that the CO2 lines are subtracted. See SPECTRA, chapter D. See also the example of measuring aromatics under the topic SEQUENCE ANALYSIS.