Table 5.
Mean concentrations and variations of O3 at major cities in Bangladesh before and during lockdown
| City | O3 (Dobson unit) | Variation* | |||||
|---|---|---|---|---|---|---|---|
| 2019a | 2019b | 2020a1 | Average# | 2020b1 | Net | Percent (%) | |
| Sylhet | 251.04 | 275.34 | 286.18 | 270.85 | 290.61 | 4.43 | 1.55 |
| Rangpur | 254.35 | 278.64 | 294.12 | 275.70 | 293.56 | − 0.56 | − 0.19 |
| Rajshahi | 251.24 | 277.05 | 286.76 | 271.68 | 290.37 | 3.61 | 1.26 |
| Narayanganj | 250.47 | 275.84 | 279.56 | 268.62 | 287.86 | 8.3 | 2.97 |
| Khulna | 250.22 | 275.27 | 276.65 | 267.38 | 286.6 | 9.95 | 3.60 |
| Gazipur | 250.83 | 275.73 | 281.16 | 269.24 | 288.53 | 7.37 | 2.62 |
| Dhaka | 250.66 | 275.9 | 280.76 | 269.11 | 288.18 | 7.42 | 2.64 |
| Chattogram | 249.07 | 274.61 | 271.95 | 265.21 | 285.75 | 13.8 | 5.07 |
| Barisal | 250.23 | 274.8 | 275.2 | 266.74 | 285.85 | 10.65 | 3.87 |
aAverage of daily concentration from 1 February to 25 March; a1O3 concentration before the lockdown; baverage of daily concentration from 26 March to 30 May; b1O3 concentration during the lockdown; *variation before and during the COVID-19 lockdown period; #average concentration of 2019a, 2019b, and 2020a