air
blue
chimney
contaminant
contamination
danger
dioxide
dirty
ecology
effect
emitting
energy
environment
environmental
factory
fume
gas
global
greenhouse
health
impurity
industrial
industry
nature
oxygen
pipe
plant
pollutant
polluter
polluting
pollution
powerplant
problem
problems
protection
sky
smog
smoke
smoky
steam
technology
toxic
warming
water
white