Columbia subject headings:
Air quality management--Government policy--United States.
Air--Pollution--Law and legislation--United States.
Emissions trading--Law and legislation--United States.
Mercury--Environmental aspects--United States.
Harvard subject headings:
Air quality management--Government policy--United States
Air--Pollution--Law and legislation--United States
Emissions trading--Law and legislation--United States.
Mercury--Environmental aspects--United States.
Princeton subject headings:
Air quality management--Government policy--United States.
Air--Pollution--Law and legislation--United States.
Emissions trading--Law and legislation--United States.
Mercury--Environmental aspects--United States.