Table 2.

Mean concentrations and variations of NO₂ at major cities in Bangladesh before and during lockdown

City	NO2 (μmol/m2)					Variation*
	2019a	2019b	2020a1	Average#	2020b1	Net	Percent (%)
Sylhet	46.12	30.84	40.5	39.15	31	− 9.5	− 23.46
Rangpur	32.68	28.51	35.56	32.25	33.87	− 1.69	− 4.75
Rajshahi	58.53	43.32	54.1	51.98	42.92	− 11.18	− 20.67
Narayanganj	248.44	95.61	278.32	207.46	85.62	− 192.7	− 69.24
Khulna	49.23	34.02	46.84	43.36	30.24	− 16.6	− 35.44
Gazipur	189.31	153.3	225.41	189.34	83.76	− 141.65	− 62.84
Dhaka	212.51	103.6	221.9	179.35	68.73	− 153.17	− 69.03
Chattogram	115.09	71.78	90.3	92.39	58.57	− 31.73	− 35.14
Barisal	39.61	25.84	39.3	34.92	24.34	− 14.96	− 38.07

^aAverage of daily concentration from 1 February to 25 March; ^a1NO₂ concentration before the lockdown; ^baverage of daily concentration from 26 March to 30 May; ^b1NO₂ concentration during the lockdown; *variation before and during the COVID-19 lockdown period; ^#average concentration of 2019a, 2019b, and 2020a