@article {1283,
	title = {Evidence for changing the critical level for ammonia},
	journal = {Environmental Pollution },
	volume = {157},
	year = {2009},
	pages = {1033-1037},
	author = {Cape, J.N and van der Eerden, L.J. and Sheppard, L.J. and Leith, I.D. and Sutton, M.A.}
}
