Columbia subject headings:
Automobiles--Motors--Exhaust gas--Environmental aspects--United States.
Automobiles--Motors--Exhaust gas--Physiological effect--United States.
Automobiles--Motors--Exhaust gas--Toxicology--United States.
Harvard subject headings:
Air--Pollution--United States
Automobiles--Motors--Exhaust gas--Environmental aspects--United States.
Automobiles--Motors--Exhaust gas--Physiological effect--United States.
Automobiles--Motors--Exhaust gas--Toxicology--United States.
Automobiles--Motors--Exhaust gas--United States--Physiological effect.
Princeton subject headings:
Automobiles--Motors--Exhaust gas--Environmental aspects--United States.
Automobiles--Motors--Exhaust gas--Physiological effect--United States.
Automobiles--Motors--Exhaust gas--Toxicology--United States.