air
brown
building
chimney
co2
danger
dark
dioxide
dirty
electricity
energy
environment
environmental
factory
fog
fumes
gas
generation
geo
global
grunge
hot
industrial
industry
light
manufacturing
pipe
plant
pollution
power
problem
risk
safety
saving
sky
smog
smoke
station
steam
sun
sunbeam
sunlight
sunset
technology
tecnology
warming
yellow