Assessment of temporal shifting of PM(2.5), lockdown effect, and influences of seasonal meteorological factors over the fastest-growing megacity, Dhaka

Dhaka is subjected to high pollution levels throughout the year, holding some relatively high amounts of pollution readings, making its air unhealthy to breathe. The study examined hourly, shifting, seasonal fluctuations in particulate matter (PM(2.5)), the effects of seasonal meteorological variables, and the lockdown effect over the megacity of Dhaka from 2019 to 2021 using data from AirNow. The results indicate the daily average PM(2.5) concentration between 2019 and 2021 was 112.49 µg/m(3), about four times higher than the WHO limit and two times higher than the Bangladesh standard. Daily PM(2.5) concentrations was high during morning and evening pick-up hours, reaching a maximum hourly concentration of 472.9 µg/m(3) in February 2020. The maximum average PM(2.5) concentration was 211.23 µg/m(3) in March 2021 (winter season), and the lowest average was 27.58 µg/m(3) in August 2020 (rainy season). The Pearson correlation coefficient (r) between the PM(2.5) and meteorological variables were inverse with rainfall (− 0.62), temperature (− 0.73), humidity (− 0.82), but positive with wind (0.09). Daily average Air Quality Index (AQI) concentrations improved from 108.53 to 67.99 µg/m(3) during the lockdown period. Finally, the study recommended many mitigation strategies that might assist accountable authorities in lowering the number of life-threatening components in the air.