acid
air
atmosphere
background
chemistry
chimney
city
civilization
cloud
contamination
dioxide
ecology
emissions
environment
environmental
factory
fuel
fume
gas
global
heat
heating
hot
hydroelectric
industrial
industry
manufacturing
ozone
pairs
pipe
poison
pollute
pollution
power
processing
red
reek
sky
smog
smoke
smokestack
smoking chimneys
stack
steam
striped
toxic
warming
white