Relationship between concentration and intensity of odours for pig slurry and broiler houses

Relationships were derived between odour concentration and odour intensity for odour emissions following land spreading of pig slurry and emissions from broiler houses. Data were obtained from trials conducted between 1987 and 1990. Odour concentration measurements were made by 50% threshold determination using a dynamic dilution olfactometer with a forced-choice type presentation to a panel of people. Odour intensity measurements were made using the same equipment and required panellists scoring their perception of the intensity of an odour at a range of concentrations according to a category scale ranging from 0 (no odour) to 6 (extremely strong odour). Intensity was related linearly to the logarithm of concentration. Significant differences (p = 0·05) were found between relationships derived for odours from pig slurry and odours from broiler houses. For odours from pig slurry the derived relationship was, Intensity = 1·61 (log10 Concentration) + 0·45 and for broiler house odours, Intensity = 2.35 (log10 Concentration) + 0.30 indicating higher intensity per unit concentration for the broiler house odours. These relationships could be useful in estimating the reduction in odour concentration required to reduce the perceived intensity of the odour to acceptable levels and, when used in conjunction with dispersion models, in determining minimum acceptable distances between the odour source and potential complainants.