acid
air
asthmatic
blue
chemical
city
clear
cloud
coal
condensation
construction
damage
dioxide
energy
environment
environmental
factory
fog
fossil
fuel
fumes
gas
generation
global
industry
layer
ozone
pipe
plant
pollution
power
problems
refinery
sky
smog
smoke
stack
steam
stratosphere
substance
technology
tower
toxic
warming
white
wind