area
atmosphere
blue
chemical
chimney
city
cityscape
climate
cloud
danger
day
dioxide
dirty
district
ecology
energy
engineering
environment
factory
fog
fumes
gas
global
industrial
industry
landscape
manufacturing
metal
nature
pipe
pipes
plant
pollution
power
process
sky
smog
smoke
smokestack
steam
steel
technologic
technology
tower
toxic
tube
warming