Columbia subject headings:
Acid rain--Europe.
Acid rain--Law and legislation--Europe.
Acid rain--Law and legislation--North America.
Acid rain--North America.
Harvard subject headings:
Acid rain--Europe.
Acid rain--Law and legislation--Europe.
Acid rain--Law and legislation--North America.
Acid rain--North America.
Princeton subject headings:
Acid rain--Europe.
Acid rain--Law and legislation--Europe.
Acid rain--Law and legislation--North America.
Acid rain--North America.