http://www.epa.gov/acidrain/#what

http://www.pnuma.org/bienal/album/pages/WozniakPNUMA_tif.htm

http://www.lacity.org/SAN/wpd/WPD/residents/howucnhp.htm

http://www.macgregoss.eq.edu.au/qldwebchall/pollution2/index.htm

http://www.grsites.com

http://www.epa.qld.gov.au/environmental_management/water/caring_for_our_water/

http://www.daienv.com/site/epage/13992_419.htm

http://www.science.org.au/nova/015/015key.htm