The principle of photoacoustic measurement is adopted in the measurement of the on-line monitoring instrument for lampblack (light with special frequency will cause the stimulated volume change of the corresponding substance or gas in the gas chamber, and the gas will be transmitted to the outside as the conducting medium, which is similar to the sound pressure, so we can know the concentration by measuring the sound pressure. ), good consistency, less interference.

non-methane total hydrocarbons: electrochemical principle.

particulate matter: principle of laser scattering.