Gas concentrations were determined by FTIR using a portable
multi-component Gasmet DX-4015 analyser (Gasmet Technologies,
Finland). In experiment 1, gaseous samples were measured only
once at day 42 in the presence of birds and excreta without litter
material (birds on raised wire floor). In experiment 2, emissions
were measured at day 24 and day 32 from birds, excreta and litter.
Chamber lids were closed for approximately 15 min before sample
collection. Water was used to seal the chambers. At that time there
was zero air exchange and odorants were allowed to concentrate
prior to sampling. Carbon dioxide (CO2) and oxygen (O2) levels
inside chambers were recorded during the period of closure and
remained at levels less than 2% (CO2) and more than 18% (O2),
respectively. The FTIR was set up as follows: flushing time, 30 s;
pumping time, 1 min; measuring time, 3 min. The gas samples were
drawn at a flow rate of 2 L/min with the in-built pump in FTIR (i.e.