Quantification of Ammonia and Greenhouse Gases in Ambient Air of a Livestock House Using a Single Near-Infrared Cavity-Ring Down Spectroscopy Instrument

Ammonia is a toxic pollutant that has harmful effects on human health and the environment. Agricultural activities and processes, such as fertilizer use, decomposition of biological material and animal excretions, account for most of the NH3 emitted into the atmosphere. Research studies that characterize and quantify NH3 emissions in livestock environments have been pivotal in assessing the issue and in helping agencies craft environmental regulations. Measuring NH3 emissions in naturally ventilated livestock houses is technically challenging due to irregular air flow patterns and low concentration levels. To this day, no general agreement on a reference technique has been established. In response, at a dairy farm part of the Flemish Institute for Agriculture and Fisheries Research (ILVO), a sampling line system was installed throughout the barn to measure NH3 levels in various locations using an in-situ, real-time NH3 analyzer - a Picarro G2508. The instrument is a high-precision cavity ring-down spectrometer (CRDS) using a near infra-red laser source capable of simultaneously measuring CO2, CH4, N2O, NH3 and H2O. In parallel, NH3 concentrations were also measured with an open-path tunable diode laser (OPL) system. We present the findings of this study, focusing on (1) comparing NH3 measurements between the OPL and the Picarro instrument, (2) evaluating the measurement accuracy of G2508 on NH3 and greenhouse gases under different conditions, and (3) investigating spatial variability of gas concentrations in the barn. Results show that at large outlet vents of the dairy barn, NH3 concentrations range from 0 to 3 ppm but remains mostly below 1 ppm.