Field Measurements of Tropospheric OH by Long-Path UV Laser Absorption

Summary

Due to its predicted concentration and high reactivity the OH radical is generally accepted as the most important driving agent of chemical conversion and transformation in the troposphere. Moreover, since its concentration level is strongly coupled to solar radiation and the mixing ratios of a large number of atmospheric trace constituents (which are all variable in space and time), a direct measurement of OH provides one of the most sensitive tests of tropospheric chemical models. In the present paper we report on a double-beam long-path UV-laser absorption technique recently developed in our laboratory. This technique improves on previously applied laser absorption methods by the use of sub-Doppler resolution analysis laser lines as well as a reference laser beam. First tests show that our method provides the required detection sensitivity.