ABSTRACT
There is a huge range of atmospheric pollutants and for a given pollutant there may be several commercially available detection systems. Some applications may require response times of seconds or less. Odors are a very common cause of complaint. In this case the complainant perceives fluctuations in concentration over periods of a few seconds, while he may become inured to steady concentrations over periods of minutes. Photons may initiate transitions between combinations of the above levels; observed molecular spectra thus tend to be extremely complicated, having structure over all scales of wave number. Atomic spectra, e.g., from a monatomic gas like Hg, are simpler, since there are no vibrational or rotational modes.
