Air hygiene in a pullet house: spatial homogeneity of aerial pollutants.

1. The spatial distribution of aerial pollutants was measured in a large deep-litter pullet house, initially holding 10,000 birds, at 12 sites within the birds' breathing zone: on 6 occasions when the birds were between 8 and 27 d of age and on two occasions when the birds were 29 and 34 d of age and the flock size was halved. 2. The distribution of most pollutants appeared uniform, implying that all sites could be considered representative of the overall concentration of pollutant. 3. The concentration of ammonia differed between sites, probably because of local variations in the rate of release from the litter. The number concentration of non-respirable particles (greater than 5 microns in diameter) became heterogeneous when the flock size was halved. 4. The operation of two punka fans had no effect on the spatial distribution of aerial pollutants, but increased the maximum air speed from 0.08 to 0.16 m/s. 5. Recommendations are given for the minimum number of sampling sites necessary for a predetermined level of statistical accuracy. Eight sites at least are recommended for most aerial pollutants, though more are needed for the concentration of gaseous ammonia.