In Situ Measurements of Tropospheric OH Radicals — A Challenge for the Experimentalist

A method for monitoring tropospheric OH and other tropospheric trace gases is discribed which makes use of differential absorption spectroscopy and is based on the fast scanning of a narrowband, frequency‐doubled, and power‐stabilized dye laser. Due to the fast scanning and the power stabilization the fluctuations of the atmosphere and the light source are minimized thus a detection limit better than 10−5 can be achieved for atmospheric long‐path absorption measurements. In a first test in the near of Frankfurt/Main tropospheric OH was observed with an averaged concentration of 1 · 106 OH cm−3. The absorption path‐length was 800 m and the acquisition time 5 min.