Validation of flux chamber technique for estimating gas emission in situ from naturally-ventilated facilities

Many agricultural enterprises use naturally-ventilated animal housing and manure storage facilities, where it is difficult to accurately monitor emissions along large open sidewalls. Another approach to field measurement of gaseous emissions from naturally-ventilated facilities lies in measuring the gas as it volatizes from the source by means of enclosed flux chambers located over the manure. The objectives of this work were: (1) To develop a barn-rugged, portable non-steady-state flux chamber system with uniform internal, horizontal air flow for in situ measurement of ammonia emissions from manured surfaces; and (2) To validate this measuring system by comparing flux chamber emission rates from dairy cow manure with whole building emission rates, calculated from the ammonia mass balance in an experimental room The average disagreement for the two methods of estimating ammonia emission flux from manure over 54 measurements was 32% (SE 3%). The magnitude of emission rate from the approximately 68 kg (150 lb) of fresh dairy manure having a surface area of 7.4 m² (80 ft ²) was 49 mg NH₃/min (standard error [SE] 2.2) for the flux chamber method and 66 mg NH₃/min (SE 2.7) for the ammonia mass balance on the room for a 26% underestimation of the emission rate by the flux chamber. Accuracy of the flux chamber with the recirculation flow method is comparable to that reported in the literature for other available methods.