air
atmosphere
breathing
carbon
chemical
chimney
climate
cloud
concentration
contamination
crisis
damage
dioxide
dirty
earth
ecology
electricity
emission
energy
environment
environmental
exhaust
factory
fuel
fume
gas
global
industrial
industry
manufacturing
outdoors
oxygen
ozone
pipe
plant
pollution
power
problem
production
safety
saving
sky
smog
smoke
smokestack
stack
steam
technology
tower
toxic