TABLE 6. Changes in Air Pollutants Induced by COVID-19 Related Lockdown Measures (’−’ Sign inDicates a Decrease and ’+’ Sign Indicates an Increase in Pollutants).
| Study |
 , 
|
 , 
|
 , 
|
 |
 |
|---|---|---|---|---|---|
| [93] | – | −33% 
|
−15% 
|
– | – |
| [96] | – | – | −4% (for lockdown), −47% for post lockdown with previous year | – | – |
| [97] | – | −(36.9 - 41.6)% | −(6.6 - 14.2)% | – | + (11.6 - 33.8)% |
| [98] | – | −18% | – | – | +50% |
| [99] | – | −50% 
|
– | – | – |
| [100] | – | −36% 
|
Insignificant change | – | – |
| [101] |
 Decreased |
 Decreased |
Both Decreased | Decreased | Increased |
| [102] | −8.8% 
|
−20.4% 
|
−26% 
|
−17.5% | −9.7% |
| [103] | Decreased 
|
Decreased NO & 
|
Decreased  & 
|
– | Decreased |
| [107] | Insignificant  change |
−63%  (fell by 24ug/m3) |
−63% 
|
Insignificant change | – |
| [109] | – | −33% 
|
−7% 
|
−7% | – |
| [111] | −(7–11)% 
|
− (23 - 37)% 
|
−(14 - 20)%  , −(7 - 16)% 
|
−(2 - 20)% | – |
| [112] |
 decreased |
−(36–53)% 
|
 Decreased |
– | Decreased |