Trees are very effective at capturing both gaseous and particulate pollutants from the atmosphere. But
while studies have often focussed on PM and NOx in the urban environment, little research has been
carried out on the tree effect of capturing gaseous emissions of ammonia in the rural landscape. To
examine the removal or scavenging of ammonia by trees a long-range atmospheric model (FRAME) was
used to compare two strategies that could be used in emission reduction policies anywhere in the world
where nitrogen pollution from agriculture is a problem. One strategy was to reduce the emission source
strength of livestock management systems by implementing two ‘tree-capture’ systems scenarios e tree
belts downwind of housing and managing livestock under trees. This emission reduction can be
described as an ‘on-farm’ emission reduction policy, as ammonia is ‘stopped’ from dispersion outside the
farm boundaries. The second strategy was to apply an afforestation policy targeting areas of high
ammonia emission through two planting scenarios of increasing afforestation by 25% and 50%. Both
strategies use trees with the aim of intercepting NH3 emissions to protect semi-natural areas. Scenarios
for on-farm emission reductions showed national reductions in nitrogen deposition to semi-natural
areas of 0.14% (0.2 kt NeNHx) to 2.2% (3.15 kt NeNHx). Scenarios mitigating emissions from cattle and
pig housing gave the highest reductions. The afforestation strategy showed national reductions of 6%
(8.4 kt NeNHx) to 11% (15.7 kt NeNHx) for 25% and 50% afforestation scenarios respectively. Increased
capture by the planted trees also showed an added benefit of reducing long range effects including a
decrease in wet deposition up to 3.7 kt NeNHx (4.6%) and a decrease in export from the UK up to 8.3 kt N
eNHx (6.8%).