air
building
business
chemical
chimney
cloud
danger
dioxide
dirty
ecology
electricity
energy
environment
factory
fog
fuel
fumes
gas
generator
global
high
hot
industry
landscape
line
manufacturing
nature
orange
pipe
plant
pollution
power
red
silhouette
sky
smog
smoke
stack
station
steam
steel
structure
sun
sunrise
sunset
technology
tower
twig
warming
water