air
building
business
chemical
chimney
cloud
co2
contamination
damage
danger
day
dioxide
dirty
ecology
energy
environment
environmental
factory
fog
fuel
fumes
gas
global
grunge
industrial
industry
large
manufacturing
nature
pipe
plant
pollution
power
problem
sky
smog
smoke
steam
steel
structure
sun
sunset
technology
tower
toxic
vapor
warming
waste
white