air
atmosphere
blue
blue sky
carbon
carbon dioxide
chemical
chimney
climate
cloud
coal
contamination
damage
danger
dirty
ecology
electricity
emission
energy
environment
environmental
environmentally friendly
exhaust
factory
fuel
fume
gas
global
industrial
industry
manufacturing
nature
ozone
pipe
pollute
pollution
problem
production
refinery
sky
smog
smoke
smokestack
steam
technology
toxic
tree
white
white smoke