Improved passive flux samplers for measuring ammonia emissions from animal houses, part 1: Basic principles

At present, precise, expensive and laborious methods with a high resolution in time are needed, to determine ammonia emission rates from animal houses. The high costs for equipment, maintenance and labour limit the number of sites that can be measured. This study examines a new, simpler concept for carrying out these measurements. The basis of the concept is a passive ammonia flux sampler, which improves on Ferm's original design by having a central orifice (thus halving the number of tubes per sampler and hence halving the number of analyses needed) and also by having a greatly increased ammonia-capturing capacity. Sets of the samplers can be placed in ventilation ducts, or in openings of a naturally ventilated animal house, to give a direct and simple measure of ammonia flux and hence of overall ammonia emission rate. Calibration of any sampler design based on this new concept is quick and easy: this is important because of the huge variation in designs of systems for ventilation in animal houses. Moreover, no power source is needed to perform cheap and accurate time-integrated ammonia emission measurements. The high ammonia-capturing capacity, allowing a long-term exposure, of at least 1 week, is achieved by using a glass-fibre insert to hold a large charge of a mineral acid. First results from validation tests with the simplest possible sampler design on the farm were promising. The flux samplers proved easy to handle and deploy, and gave results which agreed closely with those from a reference method based on fan-wheel anemometers to give ventilation rate and on the continuous measurement of ammonia concentration by chemiluminescence. In a companion paper, the performance of different forms of the flux sampler as a function of angle of incidence of airflow is reported