Measurements of tropospheric OH concentrations - a comparison of field data with model predictions

Using long path UV absorption spectroscopy we have measured OH concentrations close to the earth's surface. The OH values observed at two locations in Germany during 1980 through 1983 range from 0.7 x 10 E6 to 3.2 x 10 E6 cm E-3. Simultaneously we measured the concentrations of O3, H2O, NO, NO2, CH4, CO, and the light non methane hydrocarbons. We also determined the photolysis rates of O3 and NO2. This allows calculations of OH using a zero dimensional time dependent model. The modelled OH concentrations significantly exceed the measured values for low NOx concentrations. It is argued that additional, so far unidentified, HOx loss reactions must be responsible for that discrepancy. (IFU)