The air quality of Dhaka – world's second least livable city in terms of pollution – had started to improve after the government declared nation-wide shutdown from the last week of March to contain the Covid-19 pandemic.
According to some researchers, the air quality of the city remained moderate during April and May, the best in the last couple of years that were marked by massive construction works, including the metro-rail project.
During the two-month shutdown, almost all the construction and repair works, transportation and industrial emissions remained halted, allowing the environment to be filled with fresh air.
The newly-clean environment has given rise to hopes that positive change in Dhaka's lethal air pollution may be possible despite years of failure. Moreover, links between poor air quality and health hazards that worsen the survival of Covid-19 patients now make tackling pollution more pressing than ever.
"Several studies show that Dhaka's air quality improved by more than 30 percent during the general holidays. As the shutdown is withdrawn, coordinated efforts and strict implementation of environmental policies and guidelines are crucial so that the air quality do not deteriorate like the past," said Md Ziaul Haque, air quality management wing director of the Department of Environment (DoE).
According to the World Health Organization's estimation, five of the top 10 diseases that cause death in Bangladesh are linked to air pollution.
In 2016, research sponsored by the health ministry found that more than one lakh deaths across the country were linked with the exposure to PM 2.5 (particulate matter) - the ultrafine air pollutant, less than 2.5 microns in diameter.
"Brick kilns, vehicles' emission, road and building construction, open waste or biomass burning and trans-boundary flow of mass carbon are the major pollutants of air, particularly for Dhaka," said Professor Ahmed Kamruzzaman Majumder, chairman of the Department of Environmental Science of Stamford University Bangladesh.
To measure the impact of the Covid-19 general holidays on air quality in Dhaka city, Kamruzzaman studied data of PM 2.5 variation, aerosol optical depth, nitrogen oxide variation, carbon monoxide and black carbon concentrations during March to May, since 2016.
While presenting his study in a webinar organised by Bangladesh Poribesh Andolan on June 15, he said that the highest daily concentration of PM 2.5 between April 7 and May 16 this year was 84.9 microgram per cubic meter which was the lowest since 2017.
"Between April 7 and May 16, the average daily PM 2.5 concentration (47.6 micrograms/cubic meter) was 31.7 percent less than the corresponding period of 2019. The concentration was also less in 2020 if we compare it with 2016, 2017 and 2018," he said.
Between March 25 and May 15, the PM 2.5 concentration level grew up to 150 for only 12 days. Bangladesh National Ambient Air Quality Standard sets maximum PM 2.5 concentration at 65 micrograms/cubic meter as tolerable.
During the Covid-19 general holidays, the Aerosol Optical Depth 550 value was 0.46 and 0.53 in Terra and Aqua satellites which is less than the previous four years. Kamruzzaman found that the concentration of nitrogen dioxide also decreased by 28.5 percent during the general holidays in Dhaka.
However, the presence of nitrogen dioxide increased again from May when factories restarted.
Kamruzzaman's study also found that the concentration of carbon monoxide in the air of Dhaka decreased from 14 ppbv to 12 ppbv in April.
A concentration of 1 ppbv means that for every billion molecules of gas in the measured volume, one of them is a carbon monoxide molecule.
Dhaka's improvement less than other regional megacities
Although Professor Kamruzzaman's study shows a positive example of Dhaka's air quality improvement, US-based Lock Haven University's geology professor Md Khalequzzman has found that Dhaka's air scored less than Kolkata, New Delhi and Lahore.
In his study titled Comparative Analysis of Air Quality in Bangladesh-India-Pakistan before and after social lockdown, Khalequzzaman found that with 68 percent of better air quality time during April and May, the improvement was only 16 percent comparing the same period in 2019.
"While the AQI of Kolkata, New Delhi and Lahore improved by 26-27 percent, the lockdown in Dhaka was not effective like in these other cities," he said, adding that due to summer-time airflow from the Bay of Bengal, the air quality of Bangladesh was relatively better.
To prepare the study, Khalequzzaman collected AQI (Air Quality Index) data from the consulates of US Embassies in the respective cities.
Recommendations from shutdown-time lessons
The professors have recommended that lessons from the shutdown should be used for future air pollution control.
"Construction dust control measure should be initiated. The government should take actions to convert all diesel-run motorized vehicles to the cleaner operating fuel system. Urban vegetation like rooftop gardening should be prioritized," Kamruzzaman said.
Khalequzzaman said that the government should provide incentives to promote non-motorised vehicles like rickshaws and bicycles as well as the development of better air pollution forecasting systems.
In the first week of March this year, a high-power committee headed by the secretary for environment, forests and climate change ministry submitted an air pollution control guideline before the High Court.
In the guideline, almost all major sources of air pollutants, including plying of unfit vehicles, haphazard storing of construction materials, fire-burn brick production and burning of biomass are addressed.
DoE director Ziaul said, "Immediate implementation of the guideline was not possible due to the shutdown. However, as normalcy returns, DMP Traffic and BRTA need to control plying of hundreds of unfit vehicles strictly. At the same time, the guideline for construction works must be followed."
"If we can ensure proper implementation of the guideline, Dhaka's air will not be polluted like before March," he added.