Fine dust in Korea: four words, and what they mean
Air quality is what people here check before deciding whether to spend a day outdoors, and it is reported as a grade rather than a number. Screens on the street, the top of every weather app and the corner of the evening news all carry the same four words.
The public forecast puts the air into four graded bands rather than giving you a raw number to interpret. The band names are what appear on signs and in app headers, and the boundaries behind them are set by the national environment agency’s index.
| Grade | What it says | PM-10 (µg/m³) | PM-2.5 (µg/m³) |
|---|---|---|---|
| Good | joeum | 0–30 | 0–15 |
| Moderate | botong | 31–80 | 16–35 |
| Bad | nappeum | 81–150 | 36–75 |
| Very bad | mae-u-nappeum | 151–600 | 76–500 |
- The grade is a forecast built on a 24-hour moving average, so it describes the day rather than the minute you are standing in. A clear-looking morning inside a “bad” day is still inside a bad day.
- On the Korean-language display the four words appear exactly as written above. Matching the word is faster than converting the number.
- Both scales appear side by side because they measure different particle sizes. PM-2.5 is the stricter of the two, so it is the one that usually decides the grade you see.
We stop at what the grades mean. What to do about them — a mask, an indoor day, a change of plan — depends on your own health, and that is not a call this page is in a position to make for you.
Where this comes from
Every number on this page was read at the source rather than in a summary. Where we could not read it at the source, the page says so instead of guessing.
Questions people actually ask
- What do the Korean air quality words mean?
- There are four: 좋음 good, 보통 moderate, 나쁨 bad, 매우나쁨 very bad. Those four cover every sign and app header you will see, so recognizing the shapes is enough.
- Is the fine dust number live or forecast?
- Forecast, on a 24-hour moving average. It describes the whole day, which is why an hour that looks fine can sit inside a bad grade.
