air
atmosphere
blue
chemical
chemistry
chimney
city
climate
cloud
contamination
damage
danger
dirty
ecology
emissions
energy
environment
environmental
exhaust
factory
forest
fuel
fume
gas
global
industrial
industry
manufacturing
nature
nobody
outdoors
pipe
plant
pollution
power
sky
smog
smoke
smokestack
steam
technology
toxic
tube
warming
waste
white