Table 4.

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

City	CO (mol/m2)					Variation*
	2019a	2019b	2020a1	Average#	2020b1	Net	Percent (%)
Sylhet	0.0437	0.0456	0.0476	0.0456	0.0467	− 0.0009	− 1.89
Rangpur	0.0440	0.0473	0.0488	0.0467	0.0474	− 0.0014	− 2.87
Rajshahi	0.0436	0.0465	0.0477	0.0459	0.0469	− 0.0009	− 1.68
Narayanganj	0.0468	0.0458	0.0502	0.0476	0.0466	− 0.0036	− 7.17
Khulna	0.0448	0.0453	0.0480	0.0460	0.0472	− 0.0007	− 1.67
Gazipur	0.0469	0.0467	0.0500	0.0479	0.0474	− 0.0026	− 5.20
Dhaka	0.0476	0.0461	0.0496	0.0478	0.0468	− 0.0029	− 5.65
Chattogram	0.0435	0.0437	0.0477	0.0450	0.0453	− 0.0024	− 5.03
Barisal	0.0453	0.0461	0.0481	0.0465	0.0471	− 0.0009	− 2.08

^aAverage of daily concentration from 1 February to 25 March; ^a1CO concentration before the lockdown; ^baverage of daily concentration from 26 March to 30 May; ^b1CO concentration during the lockdown; *variation before and during the COVID-19 lockdown period; ^#average concentration of 2019a, 2019b, and 2020a