air
atmosphere
billow
billowing
canada
carbon
chemical
chimney
coal
contamination
damage
day
daytime
ecology
environment
environmental
factory
fumes
gas
gasses
global
greenhouse
halifax
harmful
hazardous
industrial
industry
manufacturing
ozone
plant
pollute
pollution
power
refinery
smog
smoke
smokestack
stack
steam
steel
sulfur
sunny
tall
toxic
vapor
warming
waste