atmosphere

black

cloud

concentration

danger

dark

dense

detail

drawing

ecology

emission

environment

exhaust

from

fuel

fumes

gases

gasoline

gray

harm

hydrocarbon

incomplete

influence

iron

metal

nitrogen

outdoor

pipe

poison

poisoning

pollution

product

protector

quality

reservoir

scale

smog

soot

spot

steam

steel

substance

tire

toxic

transparent

transport

vehicle

wheel

white