air
atmosphere
birds
black
carbon
carbon dioxide
chimney
climate
climate change
co2
concept
contaminate
contamination
dark
day
dioxide
dirty
ecology
effect
emission
environment
environmental
exhaust
factory
flock
fly
fumes
global
global warming
heat
industrial
industry
ozone
polluting
pollution
sky
smog
smoke
smokestack
stack
technology
toxic
warming