air
atmosphere
brown
building
chemical
chimney
co2
coal
danger
dioxide
dirty
ecology
electricity
energy
environment
exhaust
factory
fog
fuel
fumes
gas
global
grunge
industrial
industry
landscape
large
manufacturing
nature
oil
petroleum
pipe
plant
pollution
power
problem
production
sky
smog
smoke
stack
station
steam
steel
sun
technology
tower
toxic
vapor
warming