SmogRank / History / Country race
Countries, worst air first, day by day
Each country's typical measured city over the 30 days to every day since January 2023, worst first. Press Play to watch the order change, or drag the slider to any day.
The worst countries for PM2.5 over the 7 days to 17 Apr 2025: Hong Kong 35.8 µg/m³, Laos 30.7 µg/m³ and Chile 23.9 µg/m³.
- 1Hong Kong13 cities35.8
- 2Laos3 cities30.7
- 3Chile44 cities23.9
- 4Taiwan44 cities22.7
- 5Peru6 cities22.6
- 6Thailand85 cities19.0
- 7Mexico46 cities18.2
- 8Serbia39 cities16.2
- 9South Korea140 cities15.9
- 10Malta5 cities15.5
- 11Poland73 cities14.2
- 12Lithuania4 cities11.9
- 13Latvia4 cities11.6
- 14Hungary3 cities, was 1211.4
- 15Italy26 cities11.4
- 16Slovakia39 cities11.4
- 17Bosnia and Herzegovina5 cities11.3
- 18Czechia21 cities, was 3511.3
- 19Slovenia12 cities11.3
- 20Belgium44 cities11.0
+ 22 more countries, 10.8 µg/m³ and below
- 36United States846 cities6.5
Not counted on this day, too few cities measured: Greece since 17 Apr 2025, Ireland since 12 Apr 2025, India since 11 Apr 2025 and 4 more countries.
Countries counted each day
A country's number is its typical measured city: the median of its cities' means over the 30 days (a city needs 21 of them measured; 5 of 7 on the 7-day race), shown only with 3 such cities. A country whose monitors go quiet fades out where it stood rather than sliding down, so a gap never reads as cleaner air; "was" beside a city count marks a month after many cities joined or left. Some large countries are thin or missing because their monitors' licences don't allow reuse. How we rank.
Not covered: the government monitoring networks of China and Turkey, which publish only on their own websites; we are building the readers for them. Most cities there are missing from this board, not clean. Why.