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Contributions (%) of individual pollutants to average Air Quality Index (AQI) values in Semnan, Iran from 1 March to February 27 in 2019–2021.
| Pollutant | 2019 | 2020 | 2021 |
|---|---|---|---|
| CO | 17% | 15% | 5% |
| NO2 | 21% | 26% | 16% |
| O3 | 8% | 3% | 1% |
| PM2.5 | 54% | 45% | 78% |
PM2.5, particulate matter with an aerodynamic diameter of <2.5 μm.
