SmogRank / South Korea / Chungcheongnam-do / Seosan
Seosan, month by month
Seosan has a measured daily mean on 897 days since 23 March 2024. Its worst month was March 2025, at 81 US AQI (25.4 µg/m³), 423rd of 2,862 cities on that month's world ranking. Its cleanest was July 2026, at 43 US AQI (7.7 µg/m³). 2025 averaged 63 US AQI (15.3 µg/m³), against 58 US AQI (12.6 µg/m³) in 2024.
Every month since 2024
The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales
Months without a mean, and why
1 month
| Month | Why |
|---|---|
| Mar 2024 | 9 of 31 days measured; a month needs 22. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Seosan's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| March 2025 | 8125.4 µg/m³ | 423rdof 2,862 | Japan and South Korea, March 2025 South Korea, 9 to 11 March 2025 |
| March 2026 | 8024.7 µg/m³ | 435thof 2,971 | South Korea, 15 to 18 March 2026 |
| January 2025 | 7421.6 µg/m³ | 252ndof 2,474 | Japan and South Korea, 17 to 24 January 2025 South Korea, 13 to 14 January 2025 |
| February 2026 | 7320.8 µg/m³ | 526thof 2,866 | South Korea and Japan, 10 to 15 February 2026 South Korea, February 2026 |
| April 2024 | 7019.2 µg/m³ | 256thof 2,520 | – |
| April 2025 | 6717.6 µg/m³ | 450thof 2,951 | – |
Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.
Seosan's worst days
| Day | US AQI | Episode |
|---|---|---|
| 21 Jan 2025 | 15257.6 µg/m³ | Japan and South Korea, 17 to 24 January 2025 |
| 16 Mar 2026 | 15155.9 µg/m³ | South Korea, 15 to 18 March 2026 |
| 17 Mar 2026 | 14553.3 µg/m³ | South Korea, 15 to 18 March 2026 |
| 20 Jan 2025 | 13951.1 µg/m³ | Japan and South Korea, 17 to 24 January 2025 |
| 22 Mar 2025 | 13951.1 µg/m³ | Japan and South Korea, March 2025 |
| 15 Jan 2026 | 13348.3 µg/m³ | South Korea and Japan, January 2026 |
| 24 Nov 2025 | 13248.1 µg/m³ | South Korea and Japan, November 2025 |
| 22 Jan 2025 | 13248.0 µg/m³ | Japan and South Korea, 17 to 24 January 2025 |
| 14 Feb 2026 | 12746.0 µg/m³ | South Korea and Japan, 10 to 15 February 2026 |
| 7 Nov 2025 | 12745.9 µg/m³ | South Korea, 5 to 7 November 2025 |
Daily means, the highest since 23 Mar 2024; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.
Use this history
SmogRank, PM2.5 monthly and daily means, Seosan, South Korea, 23 Mar 2024 – 12 Oct 2026. Monitor data from Korea Air Ministry of Environment via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/kr/seosan/history (accessed 12 Oct 2026).
You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.
Seosan now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 21:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).