Ammonia monitoring in Northern Ireland – comparisons of ammonia concentrations downwind of two types of broiler house in Northern Ireland
Background to research
Intensive poultry farms are recognised to be large emission sources of atmospheric ammonia gas (NH3). Emission and deposition of NH3 from these sources can contribute substantially to total nitrogen input to sensitive receptors, and cause harmful effects by contributing to eutrophication and acidification of land and freshwaters, leading to loss of biodiversity and ecosystem change. Different ventilation designs of poultry housing may have an effect on the emission of ammonia from the buildings, and consequently the concentrations and deposition of NH3 in the vicinity of the housing.
Objectives of research
The aim of the project was to find out if there are any differences in NH3 concentrations in the vicinity of poultry housing due to ventilation design (traditional natural ventilation vs modern fanned ventilation). This information would then also contribute to the question of whether there are significant differences in NH3 emissions and environmental impacts between these poultry housing types.
Key findings and recommendations
- Monitoring of atmospheric NH3 concentrations was carried out between April and November 2004 at two similar sized poultry farms, one with natural ventilation and the other with ridge mounted fan ventilation.
- The poultry cycle at both farms coincided and it was therefore possible to carry out monitoring at the two farms at the same time, which avoided potential bias in NH3 emissions due to weather differences.
- Two sets of paired measurements were planned. However, due to problems with damageand loss of samples at one of the farms, additional measurements were made. In total, 3 sets of valid measurements were obtained for each of the two farms, with the first and final (4th) measurement periods providing paired results. Every measurement period was matched as closely as possible to the start and end of each poultry cycle (normally 6 – 8 weeks).
- Monitored NH3 concentrations along the established transect (20, 40, 80, 160 and 320 m) downwind of the farms decreased with distance away from the poultry houses, in good agreement with model predictions (ADMS model v3.1, model runs carried out by EHSNI).
- Ground level concentrations (measurement height = 1.5 m above ground) of monitored NH3 at all sampling locations downwind of the naturally vented poultry housing was about three times larger than the similar sized poultry housing with ridge mounted fan ventilation. At 20m, NH3 concentrations downwind of the naturally vented houses was 46 µg NH3 m–3 (mean of three measurement periods), compared with a mean of 17 µg NH3 m-3 from the fan vented houses (mean of three measurement periods).
- NH3 concentrations monitored at the upwind location (320 m to SW) of both farms were high, with mean concentrations of 6.7 µg NH3 m-3 and 4.8 µg NH3 m-3 measured at the naturally ventilated and fan ventilated houses, respectively. The purpose of the upwind site was to provide an indicative local “background” NH3 concentration. The high NH3 concentration is typical of sites that are located within intensive agricultural regions, and can be attributed to cattle grazing and land spreading emissions that occur in the vicinity of both farms, as well as near-source enhancement from the poultry houses at that distance.
- It is concluded that in this study a ridge fan ventilated poultry house with similar bird stocking rates provided lower NH3 concentrations in the vicinity than a naturally ventilated poultry house.
- Although further more extensive measurements at other sites are warranted, on the basis of this study, ridge fan ventilated housing would be recommended in preference to naturally ventilated housing for location immediately adjacent to sensitive receptors (e.g. designated nature reserves), since the smaller NH3 concentrations will provide lower NH3 dry deposition in the vicinity. By contrast, the large ground-level concentrations close to naturally ventilated housing will increase local NH3 dry deposition (due to high deposition velocity of NH3), therefore reducing the fraction of emitted NH3 that can contribute to long-range air pollutant transport.
Key words: Ammonia, poultry farms, natural ventilation, fan ventilation.
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