Table 2.
Air quality index (AQI).
| AQI | PM2.5 (μg/m3) 24 h | PM10 (μg/m3) 24 h | O3 (ppm) 1 ha | O3 (ppm) 8 h |
NO2 (ppb) 1 h | CO (ppm) 8 h | SO2 (ppb) 1 h |
|---|---|---|---|---|---|---|---|
| Good (0–50) | 0.0–15.4 | 0–50 | – | 0–0.054 | 0–30 | 0–4.4 | 0–20 |
| Moderate (51–100) | 15.5–35.4 | 51–100 | – | 0.055–0.070 | 31–100 | 4.5–9.4 | 21–75 |
| Unhealthy for sensitive group (101–150) | 35.5–54.4 | 101–254 | 0.125–0.164 | 0.071–0.085 | 101–360 | 9.5–12.4 | 76–185 |
| Unhealthy (151–200) | 54.4–150.4 | 255–354 | 0.165–0.204 | 0.086–0.105 | 361–649 | 12.5–15.4 | 186–304c |
| Very unhealthy (201–300) | 150.5–250.4 | 355–424 | 0.205–0.404 | 0.106–0.200 | 650–1249 | 15.5–30.4 | 305–604c |
| Hazardous (301–400) | 250.5–350.4 | 425–504 | 0.405–0.504 | b | 1250–1649 | 30.5–40.4 | 605–804c |
| Very hazardous (401–500) | 350.5–500.4 | 505–604 | 0.505–0.604 | b | 1650–2049 | 40.5–50.4 | 805–1004c |
a
Areas are generally required to report the AQI based on 8-h ozone values. However, there are a small number of areas where an AQI based on 1-h ozone values would be more precautionary. In these cases, in addition to calculating the 8-h ozone index value, the 1-h ozone value may be calculated, and the maximum of the two values reported.
b
8-hour O3 values do not define higher AQI values (≥301). AQI values of 301 or higher are calculated with 1-h O3 concentrations.
c
1-hour SO2 values do not define higher AQI values (≥200). AQI values of 200 or greater are calculated with 24-h SO2 concentrations.