air
brown
chimney
co2
color
danger
dioxide
dirty
energy
environment
factory
fog
gas
generation
geo
global
grunge
hot
industrial
industry
large
manufacturing
pipe
plant
pollution
power
problem
risk
safety
saturated
saving
sky
smog
smoke
space
station
steam
steel
sun
sunbeam
sunlight
supply
technology
warming
wire
yellow