Air quality·ozone 200
ozone 200ppb
AQI 300
very unhealthy · very bad

ozone 200 ppb — AQI 300

ozone at 200 ppb scores 300 on the US index, and the Korean grade calls it very bad.

Both systems agree here

Concentration
200 ppb
US index (AQI)
300
US category
very unhealthy
Korean grade
very bad
Concentration that makes 100
70 ppb

Same number, different verdict

A Korean forecast calls PM10 of 150 "bad", but the same value in the US index is 98 — still moderate. The other way round, PM2.5 of 40 has only just crossed into "bad" in Korea while the US index already reads 112, unhealthy for sensitive groups. Neither is wrong; they hold different rulers. Move country and the same air reads differently.

Nearby cells

180 ppb
AQI 279

Same pollutant, other concentrations

10 ppb
AQI 9
20 ppb
AQI 19
30 ppb
AQI 28
40 ppb
AQI 37
50 ppb
AQI 46
54 ppb
AQI 50
60 ppb
AQI 69
70 ppb
AQI 100
80 ppb
AQI 134
85 ppb
AQI 150
90 ppb
AQI 163
100 ppb
AQI 188
110 ppb
AQI 206
120 ppb
AQI 217
140 ppb
AQI 237
160 ppb
AQI 258
180 ppb
AQI 279
200 ppb
AQI 300

How to read this

  • On the left is the US index, on the right the Korean grade — the same concentration measured with two rulers.
  • Index values of 50, 100 and 150 are the boundaries; that is where the category name changes.
  • Forecast grades are usually daily averages, not the reading at this moment.
  • The cigarette figure is only for PM2.5 and assumes a full day of exposure.

Frequently asked questions

Q. How bad is ozone at 200 ppb?

300 on the US index, and very bad on the Korean scale.

Q. Do the two systems agree?

Yes, both read it the same way here.

Q. What concentration would make the index 100?

70 ppb. This page is at 200 ppb.

Q. What is this pollutant?

ozone. The cigarette comparison is only applied to PM2.5.