Columbia subject headings:
Air--Pollution--Congresses.
Hazardous substances--Environmental aspects--Congresses.
Pollutants--Environmental aspects--Congresses.
Harvard subject headings:
Air quality management--Congresses
Air--Pollution--Congresses
Hazardous substances--Environmental aspects--Congresses.
Princeton subject headings:
Air quality management--Congresses.
Air--Pollution--Congresses.
Hazardous substances--Environmental aspects--Congresses.