air
atmosphere
background
building
chemical
chimney
city
climate
cloud
clouds
contamination
damage
danger
dioxide
dirty
ecology
emission
energy
environment
environmental
factory
fog
fuel
fume
gas
global
industrial
industry
landscape
nature
ozone
pipe
plant
pollution
power
sky
smog
smoke
smokestack
snow
steam
sun
sunset
technology
tower
toxic
warming
white
winter