Columbia subject headings:
Air--Pollution--International cooperation--Congresses.
Air--Pollution--Law and legislation--Canada--Congresses.
Air--Pollution--Law and legislation--United States--Congresses.
Canada--Foreign relations--United States--Congresses.
United States--Foreign relations--Canada--Congresses.
Harvard subject headings:
Air--Pollution--International cooperation--Congresses.
Canada--Foreign relations--United States.
United States--Foreign relations--Canada.
Princeton subject headings:
Air--Pollution--International cooperation--Congresses.
Air--Pollution--Law and legislation--Canada--Congresses.
Air--Pollution--Law and legislation--United States--Congresses.
Canada--Foreign relations--United States--Congresses.
United States--Foreign relations--Canada--Congresses.