A double-beam UV-laser differential absorption method for monitoring tropospheric trace gases

A method is described which uses the differential absorption of a narrow-band tunable ultra-violet laser for integrated measurements of tropospheric trace gas concentrations over a path length of 12.8 km, at near ground level. A XeCl excimer laser serves as a reference beam to compensate for turbulence-induced intensity losses. After suitable statistical averaging the method is capable of detecting differential absorptions as low as 10^-4, enabling the simultaneous detection of SO₂, CH₂O and of OH radicals around 308 nm.