Seoul, South Korea Air Quality & Smog

Dominant pollutants, when pollution and smog are worst, a notable historical episode, and the official monitoring agencies for Seoul, South Korea — plus how to check the current reading. Seoul reports air quality on the Comprehensive Air-quality Index (CAI) — our full guide explains how that scale works and how it compares to the US AQI.

Dominant pollutants

PM2.5, PM10 (including Asian dust), ozone, NO₂.

Seasonal pattern: when smog is worst

Seoul's worst air comes in late winter and spring (roughly March to May), when local emissions, atmospheric stagnation, transboundary transport from the Asian mainland, and "yellow dust" (hwangsa) events from the Gobi and Mongolian deserts all coincide. Summer adds photochemical ozone on hot days. Heating-season particulate elevates the winter baseline.

A notable air-quality episode

In spring 2019, an unusually prolonged ultrafine-dust crisis blanketed Seoul for days, prompting emergency reduction measures and the passage of a special national act treating fine dust as a "social disaster." Spring Asian-dust warnings remain a near-annual fixture.

The local index and who runs it

Seoul reports air quality using the Comprehensive Air-quality Index (CAI), not the US AQI — so the same air can read as a different number than you may be used to. AirKorea publishes the real-time CAI and station-level readings nationwide, including Asian-dust (hwangsa) alerts during spring.

• AirKorea (Korea Environment Corporation)
• Ministry of Environment
• Seoul Metropolitan Government

How to check air quality in Seoul

For the official live reading, the agency portals above are the canonical source. To understand what the numbers mean, start with our guide to the Comprehensive Air-quality Index (CAI) and the broader comparison of world air-quality indices. Smog Report puts glanceable air quality on your iPhone — widgets, Live Activities, Siri, and Apple Watch — free and with no account.

Common questions about Seoul air quality

Why does Seoul have air-quality and smog problems?

Seoul's worst air comes in late winter and spring (roughly March to May), when local emissions, atmospheric stagnation, transboundary transport from the Asian mainland, and "yellow dust" (hwangsa) events from the Gobi and Mongolian deserts all coincide. Summer adds photochemical ozone on hot days. Heating-season particulate elevates the winter baseline.

What are the main air pollutants in Seoul?

Seoul's dominant pollutants are PM2.5, PM10 (including Asian dust), ozone, NO₂. The reading on any given day is usually driven by whichever of these is highest.

Has Seoul had a major air-quality or smog event?

In spring 2019, an unusually prolonged ultrafine-dust crisis blanketed Seoul for days, prompting emergency reduction measures and the passage of a special national act treating fine dust as a "social disaster." Spring Asian-dust warnings remain a near-annual fixture.

What air-quality index does Seoul use?

Seoul reports air quality on the Comprehensive Air-quality Index (CAI) (CAI), not the US AQI — so the same air can read as a different number than you may be used to. For live, glanceable readings on your iPhone, the free Smog Report app auto-selects the right local index for wherever you are.

Related