Performance of open-path lasers and FTIR spectroscopic systems

The accumulation of gases into our atmosphere is a growing global concern that requires considerable 12 quantification of the emission rates and mitigate the accumulation of gases in the atmosphere, especially the 13 greenhouse gases (GHG). In agriculture there are many sources of GHG that require attention in order to develop 14 practical mitigation strategies. Measuring these GHG sources often rely on highly technical instrumentation originally 15 designed for applications outside of the emissions research in agriculture. Although the open-path laser (OPL) and 16 open-path Fourier transform infrared (OP-FTIR) spectroscopic techniques are used in agricultural research currently, 17 insight into their contributing error to emissions research has not been the focus of these studies. The objective of this 18 study was to assess the applicability and performance (accuracy and precision) of OPL and OP-FTIR spectroscopic 19 techniques for measuring gas mixing ratio from agricultural sources. We measured the mixing ratios of trace gases 20 methane (CH4), nitrous oxide (N2O), and ammonia (NH3), downwind of point and area sources with known release 21 rates. The OP-FTIR provided the best performance regarding stability of drift in stable conditions. The CH4 OPL 22 accurately detected the low background (free-air) level of CH4; however, the NH3 OPL was unable to detect the 23 background values < 10 ppbv. 24