Historical clue formulations

• Air pollution portmanteau — 2023-12-02
• Air pollution portmanteau — 2022-11-21
• Pollution portmanteau — 2020-01-26
• Pollutant that's a portmanteau — 2017-11-01
• Some air pollution — 2010-05-10
• Thick urban air condition — 2004-10-18
• Smog relative — 2002-11-18
• Urban air problem — 2000-12-05
• City pollution — 1999-06-18
• Air pollution — 1999-05-27
• Sun block? — 1998-03-19
• Urban air pollution — 1998-02-11