Related Clues:

• Smog contributor
• Pipe sullier
• Combustion residue
• Something in the air
• It may be difficult to drive in
• Santa's soil
• Flue collection
• Smoky grime
• View disrupter
• Cause of an air alert
• Smokestack emission
• Unhealthy air
• It's hard to see through
• Urban problem
• Chimney sweep's concern