Columbia subject headings:
Environmental engineering--Handbooks, manuals, etc.
Pollution control industry--Handbooks, manuals, etc.
Harvard subject headings:
Environmental engineering
Free trade--OECD countries.
International trade
International trade--Environmental aspects
Pollution control equipment industry--OECD countries.
Pollution control industry--OECD countries.
Pollution control industry.
Princeton subject headings:
Environmental engineering.
International trade--Environmental aspects.
Pollution control industry.