air
atmosphere
buildings
chemical
chimney
city
cleanliness
climate
cloud
contaminate
contamination
damage
dirty
ecology
emission
emit
energy
environment
environmental
factory
field
gas
global
greenhouseeffect
hong
human
industrial
industry
kong
landscape
ozone
pipe
poison
polluting
pollution
reflection
rice
seascape
sky
smog
smoke
smokestack
steam
sunrise
sunset
technology
toxic
warming
water