Columbia subject headings:
Acid rain--Environmental aspects--Canada.
Acid rain--Environmental aspects--Government policy--Canada.
Acid rain--Environmental aspects--Government policy--United States.
Acid rain--Environmental aspects--United States.
Harvard subject headings:
Acid rain--Environmental aspects--Canada.
Acid rain--Environmental aspects--Government policy--Canada.
Acid rain--Environmental aspects--Government policy--United States.
Acid rain--Environmental aspects--United States.
Princeton subject headings: