air
atmosphere
background
blue
building
carbon
chemistry
chimney
climate
cloud
cloudy
contamination
damage
danger
dioxide
dirty
ecology
energy
environment
environmental
factory
fuel
fumes
gas
global
high
industrial
industry
overcast
pollute
pollution
production
red
sky
smog
smoke
smokestack
stack
steam
technology
three
tower
toxic
trail
vapor
warming
waste