Continuous atmospheric sulfur gas measurements aboard an aircraft: A comparison between the flame photometric and fluorescence methods

Analyzers that use the flame photometric and pulsed fluorescence techniques measured trace concentrations of S gas aboard an instrumented aircraft. Concentrations in the range of 1-20 ppbv were found at various locations over the U.S. East Coast and near Bermuda at altitudes up to 4000 m (650 mb). The response of both instruments changes significantly with ambient air pressure. In the case of the fluorescence method, a simple correction is applied to both the zero and span values. For the flame photometric instrument, the correction is more complicated, less accurate and valid only for ambient air pressures above 750 mb. A comparison between the two methods, based on several thousand 1-min averages, shows that the flame photometer produced consistently larger concentrations (27%) than the fluorescence device. Additional comparisons between the continuous monitors aboard the NOAA King Air and similar instruments aboard other aircraft sampling in parallel produced reasonable agreement.The use of two different techniques for measuring S gas establishes a range in the S gas concentration. This range is meaningful, since it delineates the contributions of the various interferences.