environmental
air
atmosphere
background
building
chemical
chimney
cloud
contaminate
contamination
dawn
dirty
ecology
emission
energy
environment
factory
fumes
gas
global
industrial
industry
landscape
orange
ozone
pipe
poison
pollute
polluting
pollution
power
silhouette
sky
skyline
smog
smoke
smokestack
smokestacks
steam
sunrise
sunset
toxic
urban
vapor
warming