PHOTOACOUSTIC SPECTROSCOPY IN LIVESTOCK BUILDINGS: INTERFERENCE EFFECTS ON AMMONIA, NITROUS OXIDE AND METHANE CONCENTRATIONS

摘要

Most countries where the livestock sector has an important social and economical place would like to reduce their emissions of ammonia and greenhouse gases. However emission estimates per building and per year are usually observed or measured with uncertainties higher than the reduction targets. Therefore mitigation strategies and public fundefficiency should benefit from progress in measurement and modeling of emissions from livestock houses. The quantification of livestock house emissions requires accurate measurements of gas concentration gradients. Infrared photoacoustic is used since decades because of selectivity, reduced drift in calibration, existence of industrialized analyzers. But even if the infrared bands selected by optical filters are narrow, unexpected interferences between gases and cascade effect can induce overestimationor underestimation of gas concentration. In livestock houses, molecules emitted by animals, the feed, the manure, the heating or motor-driven equipments can interfere with measurements of CH_4, N_2O, NH_3 and CO_2 as it is not possible to compensate allthe interferences. The aim of this study is to show how unexpected interferences in livestock houses can lead to either over/underestimation of NH_3, N_2O or CH_4 concentration (e.g. for NH_3, 12 instead of 2 mg/m3, and N_2O, 3 instead of 1 mg/m~3) and to discuss how to detect unexpected interferences and cascade effects and to decrease the uncertainty on concentration measurements.