Which Big Cities Cleaned Up Their Air? Decade trends in PM2.5 for 441 cities (Data Settles It, Episode 4)

Decade trends in annual fine particle pollution (PM2.5) for 441 cities of 300,000+ people, 2013 to 2024, from the WHO Ambient Air Quality Database (v8.0, June 2026 update). Each city's trend is fitted through every qualifying year (at least 6 years, each measured for at least 75% of the year) and expressed as the change per decade; WHO entries for districts of the same city are merged. 304 cities in 37 countries are ranked: 293 improved and 11 got worse, with a median change of -42% per decade. Only Tallinn, Adelaide, Stockholm and Halifax meet the WHO guideline of 5 µg/m³. US and UK cities are listed but not ranked because their national monitoring networks changed instruments during the period. Full dataset for Episode 4 of the YouTube channel Data Settles It: https://youtu.be/bk7iZMulxnw