The concentration of unhealthy gas is very low compared to the amount of other gases in the atmosphere and is based on the parts per million (ppm) scale.
| 0 - 50 |
Good |
| 51 - 100 |
Moderate |
| 101 - 200 |
Unhealthful (200 is a 1st Stage Alert) |
| 138 - 200 |
Health Advisory Alert |
| 201 - 275 |
Very Unhealthful (275 is a 2nd Stage Alert) |
| 275 + |
Hazardous |
|
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