Table 1.

NO₂ levels in the 12 most populated cities in Ecuador, before (March 16–31, 2019) and after COVID-19 lockdown (March 16–31, 2020). The NO₂ concentrations are expressed as a mean ± standard deviation. The reduction in air NO₂ concentrations (%) is shown.

#	City	Population (x105 people)	NO2 2019a (μmol/m2)	NO2 2020(μmol/m2)	Variation (%)
1	Guayaquila	30,4	66.51 ± 7.64	50.97 ± 6.41	−23,36
2	Quito	27,8	50.53 ± 5.30	39.21 ± 2.02	−22,41
3	Cuenca	6,4	37.66 ± 2.17	32.00 ± 0.98	−15,03
4	Santo Domingo	4,6	45.78 ± 0.82	39.19 ± 1.17	−14,40
5	Machala	3,9	41.67 ± 1.25	40.07 ± 0.92	−3,83
6	Manta	3,2	45.88 ± 1.88	42.29 ± 1.63	−7,83
7	Portoviejo	2,9	41.70 ± 1.10	36.55 ± 0.70	−12,35
8	Loja	2,7	33.81 ± 0.56	31.26 ± 0.79	−7,56
9	Ambato	2,6	37.24 ± 1.20	35.20 ± 1.63	−5,49
10	Riobamba	2,6	37.91 ± 1.07	33.77 ± 1.31	−10,91
11	Ibarra	2,2	38.93 ± 0.88	34.21 ± 0.95	−12,11
12	Esmeraldas	2,2	42.83 ± 0.89	37.90 ± 1.01	−11,50
Mean		–	43.37 ± 2.06	37.72 ± 1.63	−13,03

^aIncluding population of Durán.