The potential of NH3, N2O and CH4 measurements following the 2001 outbreak of Foot and Mouth Disease in Great Britain to reduce the uncertainties in agricultural emissions abatement

There is substantial uncertainty in the effectiveness of measures to reduce emissions of agricultural trace gases, including ammonia (NH3), methane (CH4) and nitrous oxide (N2O). The only way to test whether emission abatement programmes are successful is through monitoring of air concentrations and deposition. However, where NH3 emissions have been reduced in Europe, either through abatement policies or reductions in agricultural activity, it was difficult to demonstrate the link with reduced concentrations and deposition. The outbreak of Foot and Mouth Disease (FMD) in Great Britain in 2001 provides a major case study to test the link between agricultural emissions and air concentrations. This paper examines the spatial distribution of anticipated change in emissions and concentrations of NH3, CH4 and N2O as a result of the FMD outbreak. It then assesses the extent to which atmospheric monitoring could be used to detect the changes and attribute them to the effect of FMD. Two of the areas worst affected by FMD were selected for detailed analysis: in Cumbria (N.W. England) and in Devon (S.W. England). Compared with values prior to FMD, average agricultural emissions were reduced by as much as 50–100%, with estimated reductions in atmospheric mixing ratios of 0.7–3.3 ppb for NH3, 10–60 ppb for CH4 and 0.1–0.7 ppb for N2O. For NH3 and CH4, modelled changes are larger than the precision of analytical techniques and, where sampling is made at replicate sites, the changes are also larger than the inter-annual variability of existing monitoring data. By contrast, for N2O only the largest changes occurring in Cumbria are expected to be detectable and distinguishable from inter-annual variability. Based on the results, a measurement strategy has been established to follow NH3 and CH4 concentrations during and after the period of restocking. By comparing NH3 (a reactive gas) with CH4 (an inert tracer), the measurements aim to distinguish constraints on the link between changing emissions and air concentrations. Improving this linkage is essential to demonstrate that the economic costs of emission abatement translate into environmental benefits.