Highly Time Resolved Measurements of OH during POPCORN Using Laser-Induced Fluorescence Spectroscopy

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Abstract

Tropospheric hydroxyl radical (OH) concentrations were measured by laser-induced fluorescence (LIF) during the POPCORN field campaign in August 1994 at a rural site in the North East of Germany. Ambient air spectra were recorded by tuning the laser wavelength over a spectral region covering the Q11(3), Q21(3), and P11(1) rotational transitions of the (0-0) band in the A-X system of OH around 308 nm. The observed spectra clearly identify the OH radical in the atmosphere. Besides the OH absorption lines there was no sign of any other narrow-band spectral structure nearby demonstrating the high specificity of the method. For OH measurements with a typical time resolution of 60–100 seconds per data point the laser wavelength was tuned repetitively over small spectral intervals covering the peak position of the P11(1) OH-line and background positions. A total of 2300 measurements were recorded including diurnal cycles of OH with more than 300 data points. The OH as well as the LIF background signal data will be presented. In a first analysis the background signal will be characterized and the correlation between OH and the ozone photolysis frequency will be derived

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