Related Clues:

• Big city haze
• It might hang over your head
• It might make you short of breath
• Los Angeles bane
• Urban pall
• It may be thick in Houston
• Houston bane
• Waste material
• It may be thick in L.A. or Houston
• Airport hazard
• It flows underground
• Unhealthy urban haze
• Subject of an alert
• Discharge into the air
• Gray blanket