An experimental assessment of the O₃/H₂O interference problem in the detection of natural levels of OH via laser induced fluorescence

Using simulated tropospheric conditions in a laboratory study as well as OH field measurement data from project GAMETAG (Global Atmospheric Measurements Experiment on Tropospheric Aerosol and Gases), an experimental assessment has been completed of the O₃/H₂O/OH laser induced interference problem. These results indicate that, for the tropical marine boundary layer, the OH interference level averaged ∼38% during the GAMETAG field measurements program. The average “useable” UV laser energy employed in these boundary layer OH measurements was 165 µJ. OH interference estimates in the case of the free troposhere were substantially lower, being ∼13% for an average “useable” UV laser energy of 250 µJ. Modelling calculations suggest that the existing O₃/H₂O/OH interference problem could be reduced still further, by factors of five to six, through the use of very narrow UV laser pulses (i.e., .5 to 1 ns vs. 7 ns).