air
brown
carbon
chemical
chimney
cloud
co2
damage
danger
dirty
ecology
electricity
energy
environment
environmental
exhaust
factory
fog
fuel
fumes
gas
generation
global
industrial
industry
large
manufacturing
nature
pipe
plant
pollution
power
problem
red
silhouette
sky
smog
smoke
space
station
steam
sunset
technology
tower
toxic
urban
warming