Systems and methods for verifying that light absorption is caused by a targeted gaseous chemical compound. A first transmittance of light, either generated at, or filtered to, a first wavelength range and a second transmittance of light, either generated at, or filtered to, a second wavelength range are measured by first and second photon detectors. A ratio of the first and second measured transmittance is determined and that ratio is compared to a transmittance ratio associated with a targeted gaseous chemical compound to verify that the light absorption is caused by the targeted gaseous chemical compound.