Columbia subject headings:
Air--Pollution--United States.
Coal trade--Environmental aspects--United States.
Electric utilities--Environmental aspects--United States.
Harvard subject headings:
Air--Pollution--Law and legislation--United States
Coal trade--Environmental aspects--United States.
Electric utilities--Environmental aspects--United States.
Princeton subject headings:
Air--Pollution--Law and legislation--United States.
Coal trade--Environmental aspects--United States.
Electric utilities--Environmental aspects--United States.