Portable high precision nitrogen gas analyzer for eddy covariance flux measurements

Recent theoretical studies of eddy flux correlation have suggested that the commonly used assumption of dry air having no net flux is erroneous and can lead to significant errors in reported observations. Presently, dry air density is calculated indirectly from measured temperature, pressure and relative humidity, all of which contribute to increased uncertainties in the result. If instead the density of nitrogen, which has no net vertical flux, was measured directly, the accuracy of eddy correlation measurements could be improved substantially. Southwest Sciences, Inc. proposes to develop a portable nitrogen analyzer that would be used in conjunction with sonic anemometers to greatly improve the performance of eddy covariance flux measurements. These studies are critical for characterizing the sinks and sources of greenhouse gases. In Phase I, we will demonstrate the viability of a spectroscopic technique that can measure atmospheric nitrogen with high precision and time response, yet meet the needs of a portable field instrument. Critical tradeoffs in laser selection and analyzer design will be studied to determine the optimum operating configuration. The precision of the analyzer will be evaluated over the expected range of temperatures and pressures required for field operation.