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Average sub-air quality index (AQIi) values for air pollutants in Semnan, Iran for the study periods: before lockdown (BF), during lockdown (LD), and after lockdown (AF) in 2019–2021.
| AQI values | |||||||
|---|---|---|---|---|---|---|---|
| 2019 | 2020 | 2021 | |||||
| Pollutant | BF | BF | LD | AF | BF | LD | AF |
| CO | 37.3 | 33.3 | 31.4 | 27.4 | 50.1 | 33.9 | 31.2 |
| NO2 | 49.9 | 47.8 | 24.5 | 27.6 | 43.2 | 31.8 | 36.4 |
| O3 | 37.9 | 10.4 | 22.7 | 14.7 | 56.3 | 30.0 | 29.5 |
| PM2.5 | 109.0 | 70.1 | 39.9 | 40.5 | 55.9 | 43.1 | 51.8 |
PM2.5, particulate matter with an aerodynamic diameter of <2.5 μm.
