Influence of windbreaks on livestock odour dispersion plume in the field

Windbreaks are believed to help disperse odours emitted by livestock facilities. The objective of the project was to measure the effect of windbreaks on the size and intensity of odour dispersion plumes developed in the field when subjected to a point odour source. Comparisons were made for odour plumes observed with and without windbreaks, and with windbreaks exposed to different conditions. Besides a control site without windbreak, four windbreak sites were selected, two of which had one row of deciduous trees while the other two had one row of coniferous trees. Odour dispersion plumes were measured 6 times on the control site and 33 times on the windbreak sites. Each time, an odour generator was used to produce a controllable level of odour emission. Three groups of four trained panellists measured the size and intensity of the odour plume developing in the field downwind from the odour generator. Using a forced choice dynamic olfactometer, all 12 panellists were calibrated every test day and the group's field odour intensity perception was correlated to odour concentrations. Windbreaks were found to have an effect on odour dispersion. This effect was more pronounced when the windbreak was dense (lower optical porosity) and consisted of coniferous trees. Moreover, odour dispersion was improved when the source was located 15 m upwind from the windbreak, rather than 60 m. When temperatures were above 15 °C, odours were dispersed over a shorter distance, likely because of added convective effects. Wind speed was found to have a limited effect on the size and intensity of the odour plume while wind direction perpendicular to the windbreak reduced the size of the odour plume but not the trapping of odours on the leeward side of the windbreak. In general, windbreaks can improve odour dispersion, but a better study of their performance is required through modeling.