Table 3.

NO₂ TCVDs reduction observed during the COVID-19 lockdown period, starting on the Reference date and lasting for 21 days, relative to the same period in 2021, with the exception of China and Iran, where it lasts for 11 and 16 days respectively, in order to avoid the interference with the New Year Holidays. The percentage change is defined as (TVCDs₂₀₂₀ - TVCDs₂₀₂₁)/TVCDs₂₀₂₁ × 100%. The numbers in the brackets are standard error of the mean.

City	Lat	Lon	Reference date	NOAA-20 OMPS
Beijing	39.9	116.4	31-Jan-20	−27(±4)%
Tianjin	39.3	117.4	31-Jan-20	−33(±3)%
Shenyang	41.8	123.4	31-Jan-20	−21(±4)%
Zhengzhou	34.7	113.6	31-Jan-20	−29(±3)%
Jinan	36.7	117.1	31-Jan-20	−46(±3)%
Shanghai	31.2	121.5	31-Jan-20	3(±7)%
Chengdu	30.6	104.1	31-Jan-20	−50(±6)%
Guangzhou	23.1	113.3	31-Jan-20	−68(±3)%
Shenzhen	22.5	114.1	31-Jan-20	−56(±4)%
Hong Kong	22.3	114.2	31-Jan-20	−54(±4)%
New Delhi	28.6	77.2	25-Mar-20	−16(±2)%
Mumbai	19.1	72.9	25-Mar-20	−12(±4)%
Milan	45.5	9.2	23-Feb-20	−23(±4)%
Venice	45.4	12.3	23-Feb-20	−16(±4)%
Madrid	40.4	3.7	15-Mar-20	−32(±3)%
Barcelona	41.4	2.2	15-Mar-20	−15(±4)%
Moscow	55.8	37.6	30-Mar-20	−37(±3)%
Tehran	35.7	51.4	04-Mar-20	12(±7)%
New York	40.7	−74.0	24-Mar-20	−22(±4)%
Washington DC	38.9	−77.0	24-Mar-20	−18(±4)%
Chicago	41.9	−87.6	24-Mar-20	−17(±4)%

Note: We used OMPS global daily gridded Level-3 data at 0.25° × 0.25° and the reductions are calculated based on pixels within a 100-km radius around the city center with cloud fractions of 40% or less.