Air quality·carbon monoxide 1
carbon monoxide 1ppm
AQI 11
good · good

carbon monoxide 1 ppm — AQI 11

carbon monoxide at 1 ppm scores 11 on the US index, and the Korean grade calls it good.

Both systems agree here

Concentration
1 ppm
US index (AQI)
11
US category
good
Korean grade
good
Concentration that makes 100
9.4 ppm

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

0.5 ppm
AQI 6
1.5 ppm
AQI 17

Same pollutant, other concentrations

0.5 ppm
AQI 6
1 ppm
AQI 11
1.5 ppm
AQI 17
2 ppm
AQI 23
3 ppm
AQI 34
4 ppm
AQI 45
4.4 ppm
AQI 50
5 ppm
AQI 57
6 ppm
AQI 67
7 ppm
AQI 76
9 ppm
AQI 96
10 ppm
AQI 111
12 ppm
AQI 143
15 ppm
AQI 193
20 ppm
AQI 231
25 ppm
AQI 264
30 ppm
AQI 297
40 ppm
AQI 397

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 carbon monoxide at 1 ppm?

11 on the US index, and good 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?

9.4 ppm. This page is at 1 ppm.

Q. What is this pollutant?

carbon monoxide. The cigarette comparison is only applied to PM2.5.