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 19 Apr 2025: Hong Kong 34.9 µg/m³, Chile 25.2 µg/m³ and Taiwan 22.5 µg/m³.
- 1Hong Kong13 cities34.9
- 2Chile48 cities25.2
- 3Taiwan44 cities22.5
- 4Peru6 cities22.0
- 5Mexico45 cities21.8
- 6Laos3 cities16.8
- 7Thailand85 cities16.3
- 8Lithuania4 cities15.6
- 9South Korea140 cities15.4
- 10Malta5 cities14.7
- 11Latvia4 cities14.6
- 12Serbia39 cities13.9
- 13Poland74 cities12.6
- 14Japan538 cities11.6
- 15Slovakia40 cities9.6
- 16Czechia43 cities, was 359.5
- 17Austria35 cities9.4
- 18Italy26 cities9.2
- 19Romania11 cities9.1
- 20Bosnia and Herzegovina5 cities8.9
+ 21 more countries, 8.9 µg/m³ and below
- 30United States842 cities6.8
Not counted on this day, too few cities measured: Greece since 19 Apr 2025, Hungary since 19 Apr 2025, Ireland since 12 Apr 2025 and 5 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.