From "The Plain English Guide to The Clean Air Act"
Definitions of technical words used in summary of The Clean Air Act.
http://www.epa.gov/air/caa/peg/

U.S. EPA Terms and Acronyms
Search engine based on approved terms and acronyms from the U.S. EPA.
http://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/termsandacronyms/search.do

Terms of Environment: Glossary, Abbreviations, and Acronyms
Defines in non-technical language the more commonly used environmental terms appearing in EPA publications.
http://www.epa.gov/OCEPAterms/intro.htm