Air quality·nitrogen dioxide 20
nitrogen dioxide 20ppb
AQI 19
good · good

nitrogen dioxide 20 ppb — AQI 19

nitrogen dioxide at 20 ppb scores 19 on the US index, and the Korean grade calls it good.

Both systems agree here

Concentration
20 ppb
US index (AQI)
19
US category
good
Korean grade
good
Concentration that makes 100
100 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

10 ppb
AQI 9
30 ppb
AQI 28

Same pollutant, other concentrations

10 ppb
AQI 9
20 ppb
AQI 19
30 ppb
AQI 28
40 ppb
AQI 38
50 ppb
AQI 47
60 ppb
AQI 58
70 ppb
AQI 69
80 ppb
AQI 79
100 ppb
AQI 100
120 ppb
AQI 105
150 ppb
AQI 110
200 ppb
AQI 120
250 ppb
AQI 129
300 ppb
AQI 139
400 ppb
AQI 158
500 ppb
AQI 175
700 ppb
AQI 209
1000 ppb
AQI 259

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 nitrogen dioxide at 20 ppb?

19 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?

100 ppb. This page is at 20 ppb.

Q. What is this pollutant?

nitrogen dioxide. The cigarette comparison is only applied to PM2.5.