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 20 Apr 2025: Hong Kong 28.1 µg/m³, Chile 26.2 µg/m³ and Mexico 22.2 µg/m³.
- 1Hong Kong13 cities28.1
- 2Chile48 cities26.2
- 3Mexico46 cities22.2
- 4Peru6 cities21.3
- 5Taiwan44 cities20.5
- 6South Korea140 cities15.8
- 7Thailand85 cities15.7
- 8Lithuania4 cities15.6
- 9Latvia4 cities14.6
- 10Malta5 cities14.6
- 11Laos3 cities13.7
- 12Serbia39 cities13.1
- 13Japan540 cities12.1
- 14Poland73 cities11.5
- 15Romania10 cities9.6
- 16Slovakia39 cities9.3
- 17Brazil43 cities8.9
- 18Germany249 cities8.9
- 19Czechia43 cities, was 358.8
- 20Belgium44 cities8.7
+ 21 more countries, the next at 8.5 µg/m³
- 30United States843 cities6.7
Not counted on this day, too few cities measured: Austria since 20 Apr 2025, Greece since 19 Apr 2025, Hungary since 19 Apr 2025 and 6 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, Turkey and Iran, which publish only on their own websites. We are building the reader for China's network. The networks of Turkey and Iran don't answer requests from outside their countries, so we can't read them. Most cities there are missing from this board, not clean. Why.