Table 2.
The decline of major air pollutants in early 2020 compared to 2019, and main causes
| Country | Major pollutants reduction | Major causes | References | |
|---|---|---|---|---|
| 27 countries | NO2 | 13–44% | Closure of factories, transportation networks, and companies | Venter et al. (2020) |
| O3 | 2–20% | |||
| PM2.5 | 10–28% | |||
| New York (USA) | CO2 | 5–10% | Closure of factories, transportation networks, and companies | McGrath (2020) |
| China, Italy, France, and Spain | NO2 | 20–30% | Closure of factories, transportation networks, and companies | Leung (2020) |
| USA | NO2 | 30% | ||
| India | NO2 | 40–50% | ||
| Delhi (India) | PM2.5 | 200% | Restricted travel including flights, rail, intercity bus services and industrial activity stopped | Kotnala et al. (2020) |
| PM10 | ||||
| Western Europe | NO2 | 30–50% | – | Menut et al. (2020) |
| PM | 5–15% | |||
| São Paulo (Brazil) | CO | 64.8% | Closure of shopping malls, restaurants, fitness centers, schools, universities, and public transportation restrictions | Nakada and Urban (2020) |
| NO | 77.3% | |||
| NO2 | 54.3% | |||
| Barcelona, Madrid (Spain) | NO2 | 50% | Decreases in vehicular mobility and the volume of other relevant activities such as port and airport operations | Baldasano (2020) |
| 62% | ||||
| Rio de Janeiro (Brazil) | CO | 30.3–48.5% | Vehicle circulation restrictions, suspension of classes, and many other activities | Dantas et al. (2019), Siciliano et al. (2020) |
| NO2 | 16.8–53.8% | |||
| NOx | 24.4–46.1% | |||
| Wuhan (China) | PM2.5 | 25% | – | Leung (2020) |
| NO2 | 40% | Use of diesel vehicles stopped | ||
For instance, Wuhan city, the primary epicenters of the outbreak, has reduced NO2 by about 40%. Similarly, observations in the USA and India showed a 30–50% reduction