Ma. Sutton et al., Dispersion, deposition and impacts of atmospheric ammonia: quantifying local budgets and spatial variability, ENVIR POLLU, 102, 1998, pp. 349-361
Ammonia is a reactive pollutant emitted primarily by agricultural sources n
ear ground level in the rural environment. The consequence of these factors
is that, in addition to the effects of long-range pollutant transport, amm
onia has major effects at a local scale, with emission and receptor areas o
ften closely located in the rural landscape. There is a substantial local s
patial variability that needs to be considered in effects assessments, whil
e variations in local deposition may affect the amount of ammonia available
for impacts further afield. The wide-ranging UK programme ADEPT (Ammonia D
istribution and Effects ProjecT) has addressed these issues through a combi
nation of measurement and modelling activities concerning the distribution
of emissions, atmospheric transport, deposition and effects assessment. The
results are illustrated here by summarizing the findings of a joint experi
ment at Burrington Moor, Devon, and wider modelling contrasting the variabi
lity at a field scale with 5 km resolution estimates for the UK. The fracti
on of emitted NH3 deposited locally is shown to depend critically on the do
wnwind land-cover, with fluxes being dependent on interactions with the amm
onia compensation point. This will restrict deposition back to agricultural
land, but may mean that non-conservation woodlands could be of benefit to
recapture a significant fraction of emissions. The generalized models demon
strate the high spatial variability of ammonia impacts, with a case study b
eing used to show the consequences at a field scale. In source regions subs
tantial variability occurs at sub-1 km levels and this will have major cons
equences for the emission reduction targets needed to protect ecosystems.