Table 4.
: Historical (February, March & April 2016–2020) and lockdown (26 March 2020–17 April 2020) daily mean (24-h) concentrations for NO2, O3 PM10, PM2.5 & BC for the centURB, subURB and backURB sites.
| Site & pollutant | Concentration (μg m−3) |
Variation |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Historical |
Lockdown |
|||||||||
| Mean | Std. dev. | Std. error | Mean | Std. dev. | Std. error | (μg m−3) | (%) | t-Test | P-value | |
| centURB | ||||||||||
| PM10 | 15.3 | 1.7 | 0.3 | 12.2 | 4.5 | 1.0 | −3.1 | −20.1 | 3.0 | <0.05 |
| PM2.5 | 6.1 | 4.2 | 0.1 | 5.1 | 1.7 | 0.4 | −1.0 | −17.0 | 2.7 | <0.05 |
| NO2 | 35.7 | 12.8 | 0.6 | 23.5 | 5.7 | 1.2 | −12.2 | −34.1 | 9.1 | <0.05 |
| BC | 1.9 | 0.9 | 0.1 | 0.5 | 0.2 | 0.0 | −1.4 | −75.4 | 11.1 | <0.05 |
| subURB | ||||||||||
| PM10 | 11.5 | 3.3 | 0.2 | 9.6 | 3.1 | 0.7 | −1.9 | −16.2 | 2.7 | <0.05 |
| NO2 | 9.7 | 4.7 | 0.2 | 4.2 | 3.0 | 0.6 | −5.5 | −56.9 | 8.2 | <0.05 |
| BC | 0.6 | 0.4 | 0.0 | 0.3 | 0.2 | 0.0 | −0.3 | −55.7 | 7.1 | <0.05 |
| backURB | ||||||||||
| PM10 | 12.2 | 4.7 | 0.2 | 11.4 | 2.7 | 0.8 | −0.8 | −6.6 | 1.0 | 0.3 |
| PM2.5 | 4.4 | 1.9 | 0.1 | 4.0 | 1.5 | 0.3 | −0.4 | −8.2 | 1.1 | 0.3 |
| O3 | 33.1 | 9.0 | 0.4 | 38.6 | 7.0 | 1.5 | 5.5 | 16.7 | −3.6 | <0.05 |
| NO2 | 3.6 | 2.0 | 0.1 | 2.3 | 1.6 | 0.3 | −1.3 | −35.6 | 3.7 | <0.05 |