air
atmosphere
chemical
chemicals
chimney
co2
concrete
contaminate
contamination
cylindrical
damage
dioxide
dirty
ecology
emission
emit
energy
environment
exhaust
factory
fog
fume
fumes
global
hazard
industrial
industry
landscape
manufacturing
orange
ozone
pipe
plant
poison
polluting
pollution
problem
silhouette
sky
smog
smoke
smokestack
smokestacks
steam
tall
technology
toxic
urban
warming
yellow