Effectiveness of agricultural interventions to minimise the health impacts of air pollution: a synopsis from a mixed method study

Background Agriculture dominates United Kingdom ammonia emissions, from livestock manure exposed to the atmosphere via livestock housing, storage, land and grazing. Ammonia significantly contributes to the formation of PM 2.5 (particles with diameter of 2.5 μm or less) concentrations in Europe which are associated with adverse human health outcomes. Ammonia emissions contribute to nitrogen deposition, whereby reactive compounds of nitrogen are deposited into the biosphere, potentially resulting in biodiversity loss. Recent research has not found sufficient evidence for effectiveness of interventions to reduce ammonia emissions and little evidence on the cost-effectiveness of interventions. The current study aimed to address this knowledge gap. Aim The study aimed to assess effectiveness and cost-effectiveness of two agricultural interventions to mitigate ammonia emissions – improved housing for farmed animals and improved manure application. Methods Emission measurements were made at five farms (dairy, pig, poultry). Information on uptake of mitigation measures, barriers and enablers for implementation were determined through an online survey and focus groups with farmers, supplemented by stakeholder interviews. Chemical transport and dispersion modelling estimated population exposures to air pollution at local and national levels under three scenarios (low, medium, high intervention uptake). A health impact assessment estimated health effects associated with the scenarios, and data on self-reported health issues were collected via an online survey of rural residents. Economic evaluation methods estimated cost–benefits of the scenarios and impact on ecosystems. Results Farmers favour mitigation measures which are cheaper, and build on existing practices, such as amending diet or extending the grazing season. However, these are less effective in decreasing ammonia emissions. Scenarios based on realistic current, and future, uptake levels of measures showed little impact on air quality, partly due to the ammonia-rich United Kingdom atmosphere minimising conversion of ammonia emissions to particulate matter. Consequently, minimal impact of mitigation measures was evident on health outcomes and costs. There was no evidence that self-reported health symptoms from rural residents were related to living near a farm, type of farm or seasonality of farm activities, consistent with results of local dispersion modelling which estimated that most emissions from animal housing dispersed within 1 km. Limitations Impacts of COVID-19 and the United Kingdom’s withdrawal from the European Union on the agricultural industry affected the recruitment and availability of farms and farmers, resulting in fewer field measurements than planned. A lower response to the farmers’ survey was mitigated by the quality of data provided by participants and the successful series of focus groups. Conclusions The study highlights the need for enhanced communication with the farming community to encourage implementation of more effective mitigation measures, such as air scrubbers, or those relating to slurry storage, currently perceived to be too expensive and complex. Greater clarity on benefits is essential so that farmers understand not only what they need to do but also how and why. Future work Further investigation of the health impacts of ammonia emission should focus on those exposed on the farm, or resident nearby animal houses. Further modelling development of key atmospheric processes is also indicated to minimise uncertainties associated with the regional modelling. Funding This synopsis presents independent research funded by the National Institute for Health and Care Research (NIHR) Public Health Research programme as award number NIHR129449.