Introduction

The Economist's Intelligence Unit (EIU) publishes a list of inhabitable cities every year and sadly in 2019 Dhaka was identified as the third least livable city in the world. And air pollution is one of the regulators for bringing Dhaka down to an uninhabitable city. Apart from air pollution, there are various problems in Dhaka city including noise pollution, water pollution, river capture and pollution, waterlogging, traffic congestion, waste management, unplanned and uncoordinated road digging and many more but air pollution is still on top of all of them. The Bangladesh Poribesh Andolon (BAPA) has expressed fears that high levels of air pollution in Bangladesh could increase the number of deaths of the coronavirus. It is also feared that as the temperature drops in the coming winter season, which could lead to more air pollution, coronavirus may increase which might be a triggering factor for the second wave of COVID-19 in Bangladesh.

The relationship between air pollution and health loss

Fine particles are more dangerous than coarse particles. Among all sizes of particulate matter microscopic or ultrafine particulate matter is dominated in Dhaka due to its origin mostly from burning. A study conducted by the Center for Atmospheric Pollution Studies (CAPS) at Stamford University Bangladesh found that the amount of tiny particulate matter (PM2.5) in the air in Dhaka city is about 80 percent of the total particulate matter, which is one of the most alarming causes of lung disease. These tiny particles cause lung cancer, asthma, bronchitis, tuberculosis, kidney disease, high blood pressure, congenital disabilities, diabetics, heart attack, liver problems, effects on pregnant mothers, eye irritation, skin diseases, and impact on mental health. According to the Health Effects Institute, 1,22,400 people die every year in Bangladesh due to air pollution. According to the World Bank's 2017 report, 46,000 people die every year in Bangladesh due to air pollution. The report also said, 10,000 people die every year in Dhaka alone due to air pollution.

Air quality of Dhaka during Corona period

Analyzing the data collected through the advanced atmospheric research center at the US Embassy's own premises in Baridhara, Dhaka, it is seen that the first 24 days of March 2020 (104 µg/m3) in Dhaka the averages air quality was 15 percent and 20 percent better compare to for year 2018 (116µg/m3) and 2019 (123µg/m3) respectively (Table 1). The upward trend (average 106µg/m3) of air pollution can be noticed in the next four days after the closure of educational institutions on 16th March 2020 (from 17th March) as the movability of the scary people has increased as many people start to move to village. Similarly, after the announcement of general holiday on 25th March (from 26th March), the people were busy to leaving the capital on 25th to 27th March, which increases PM2.5 for about 19 percent (124µg/m3) higher than the average (104µg/m3) of before the general holiday (1 to 24 March 2020) (Table 1). Despite the limited movement of people during this time, it took a long time for the particles floating in the air, the long-standing dust on the leaves of trees and the dust in other installations to subside. Dhaka's air quality started getting better from 28th March and a minimum of 49µg/m3 was recorded on 30th March. Except for the first three days, the general holiday (44 days) from 28th March to 10th May, the average PM2.5 level in the air at this time (only 54µg/m3, but the average from March 25th was only 59µg/m3) before the announcement of the general holiday. The day i.e. 1 to 24 March 2020 was about 52 percent lower than the average level (104µg/m3) (Tables 1 and 2)

Table 1: Average concentration of PM2.5 in the air during the pre-Corona period of Dhaka city (March 1 to March 24) and the same period of the previous 4 years:

Note: Calculated from hourly data, a total of 47 days of data have been analyzed.

Data Source: https://www.airnow.gov/international/us-embassies-and-consulates/#Bangladesh$Dhaka

Table 2: Average concentration of PM2.5 in the air during COVID-19 general holiday in Dhaka city (March 25 to May 10) and the same period of previous 4 years:

However, in this case, it is not possible to say for sure that the general holiday and lockdown is the only reason for this improvement in Dhaka's air quality. Here the special effects of meteorological parameters such as temperature, rainfall and humidity can be noticed. For example, last Wednesday, May 6, 2020, at 4 am, the amount of PM2.5 in the air of Dhaka was 80µg/m3 and the AQI value was 176. The air quality improved considerably after the morning rain. After 11 a.m., the amount of PM2.5 in the air dropped to 7.7µg/m3 and the AQI value dropped to 32. On February 25, 2017, Dhaka's Air Quality Index (AQI) was as low as 13.

It is noteworthy that during the last 47 days of public holidays due to Covid-19 coronavirus (March 25 to May 10, 2020) the average level of PM2.5 (59µg/m3 in 2016, 59µg/m3 in 2017, 64 µg/m3 in 2018, 89 µg/m3 in 2019, 59 µg/m3 in 2020) was 7 percent and 34 percent lower than the average values for the same period in 2018 and 2019, respectively (Table 2). Surprisingly, the average level of PM2.5 for the same period in 2016 and 2017 was almost the same in 2020 during COVID-19 period. According to the Bangladesh Environmental Conservation Rules, 2007, the daily average allowable limit of PM2.5 in the air is 65µg/m3.

Air Quality Index or AQI during the COVID-19 period

Air quality index or AQI score in between 0 and 50 that air is good, if the score is 51-100 then the air quality is considered moderate or generally acceptable. If the AQI score is 101 to 150, it is considered to be unhealthy for the sensitive population, especially children, the elderly and the patients with respiratory diseases. When AQI score is 151-200, it is considered unhealthy for everyone and it is very unhealthy if AQI 201-300. If the AQI is over 301, the air is deemed to be dangerous and at this time, health warnings are considered a state of emergency for every city. Air Quality Index (AQI) is calculated considering the air pollution caused by 6 pollutants such as particulate matter or PM2.5, PM10, sulphur dioxide, carbon monoxide, nitrogen dioxide and ground level ozone. The more AQI increases, the more risky the air quality is. Under China's Beijing-based Global Air Quality Index project, air quality data is collected from 30,000 monitoring stations in 1000 cities of 100 countries worldwide. The project has its surveillance equipment at the US Embassy in Dhaka, Bangladesh. Though since 2007 they have been collecting information globally but in Bangladesh they are collecting data since March 9, 2016. The organization has been providing data on the website as well. In addition to PM2.5, temperature, precipitation and airflow are regularly measured at this station. A review of 47 days of Dhaka's Air Quality Index (AQI Score) during the Corona period of 2020 (March 25 to May 10, 2020) and the previous four years (2016 to 2019) shows that during this period of 2020, Dhaka's air quality improved of earlier years (Table 3).

Table 3: Classification of the day in Dhaka city during COVID-19 and the same period of the previous 4 years (25 March-10 May) based on the Air Quality Index (AQI):

Data shows that the number of days of (moderate and unhealthy for sensitive group) in 2020 (AQI score up to 150 and the average number of days within 65µg/m3) increased by 3% compared to 2017, 13% compared to 2018, 40% compared to 2019. But it has declined 15% compared to 2016. A continuous decline in air quality from 2016 in 2020 is seen during Corona time. During the corona period in 2020, the number of bad days (unhealthy and very unhealthy) has declined 4%, 25% and 43% compare to 2017, 2018, 2019 at same period. The number of bad days in 2020 has increased by double compared to 2016 alone.

Aerosol Optical Depth (AOD) during the period of corona

Aerosol Optical Depth (AOD) is the main optical parameter for measuring airborne particles based on satellites. According to a study by the Stamford Center for Atmospheric Pollution Studies (CAPS), the average AOD in Bangladesh declined from February 1 to May 1 in 2020 compared to the previous year. The downward trend of AOD in the atmosphere indicates a decreasing trend in air pollution. In Bangladesh, in 2017, 2018, 2019 and 2020 (March 26 to May 1), the AOD values were 0.94, 0.86, 0.74 and 0.58 respectively. From these data, it is understood that in 2020 air pollution in Bangladesh was much lower than the previous years during the COVID-19 induced lockdown.

The air quality of the other year at the same time during the corona

In general, the air quality is the better during the post monsoon (October to February), while worst during the dry season (December to February). The air quality is very good during pre-monsoon (March to May) and best during the monsoon season (June to September) (Majumder et al., 2020). Accordingly, the air quality data for the March, April and May (pre-monsoon season) of the last four years (2016-2019) showed that out of 47 days (25 March-10 May) only 35 days the value of PM2.5 in the 2020 are within the permissible level (65 µg/m3) (Table 4). On the other hand, in 2016, 2017, 2018 and 2019 it was 41 days, 34 days, 31 days and 25 days respectively. Despite the closure of most industrial factories, transport and construction work, and the impact of rain, the expected long-term and sustainable air quality progress has not been seen. The air quality in Dhaka was better in 2016 and 2017, despite the absence of such a particular pandemic situation. Naturally, the question arises: What is the source of PM2.5 in the air in Dhaka during the lockdown? Why is the PM2.5 level in Dhaka a few times higher than the daily national standard (65 µg/m3) set by the Bangladesh Government?

Table 4: Day classification based on the PM2.5 Value during COVID-19 (25 March-10 May)

Day classification based on the PM2.5 value during COVID-19 (25 March-10 May)

Annual and daily National standard for PM2.5 for Bangladesh is 15 and 65µg/m3 respectively

Note that the daily average of PM2.5 in Dhaka was 95µg/m3 and 84µg/m3 respectively on April 2 and April 7. There are reports that some brick kilns shards operational around Dhaka during the lockdown. Especially in the south, the industrial establishments and brick kilns polluted air swells in the South are causing Dhaka's air quality to deteriorate. Besides, the air quality is seen to be poor locally due to the continued movement of 20 to 30 percent of the traffic during the day and the use of the track at night to provide food and clothing products and the use of traditional stoves in low income and slum areas, burning of medical waste and burning of urban waste in some places. The closure of these sources would have improved the air quality of the capital Dhaka. Besides, the high population density and the polluted air trap or obstruction of the air due to buildings' high density. In general, the air pollution in Bangladesh is very controlled due to rain during the pre-monsoon and monsoon seasons. It is bit complicated to assess the impact of the covid-19 on air pollution because rain also has a strong role to play in controlling the air quality. The Department of Environment has not yet determined how the air quality was during lockdown or whether they has been measured or not, as no information was available on the department's website since March 22, 2020.

Future plans to combat air pollution: Lessons from COVID-19

The recent past improvement in Dhaka's air quality in the Corona situation was only temporary, in no way sustainable or permanent. This is just a positive manifestation of the particular disaster situation. But it also shows us again what the primary sources of air pollution are. It taught us how to control air pollution ad what are the benefits of preventing air pollution. Therefore, as Corona's situation improves, we must not forget the current state of air pollution-free Dhaka city, but use this experience to identify sources and adopt a plan and determination to build a livable and sustainable Dhaka city in the future. And for this, the following issues can be considered seriously:

Short-term-(Act Now): Using improved quality masks and PPEs for personal protection and safety; renovation work should be done through coordination; sprinkle water on the streets and road side trees regularly during winter; ensuring the use of covers on trucks or other vehicles that transport sand or soil or construction materials in capital Dhaka; at places where construction work is going on, contractors should cover the work to prevent the spread of dust; ensure complete road construction or excavation work or carpeting complying with laws and rules and within a minimum and scheduled time period; strict control and seize the vehicles emitting black smoke (expired and fitness less vehicles and water transports); unparalleled driving on different days of the week for alternative number plates vehicles; fix the economic life of different cars or vehicles as per section 36 of the road transport act 2018 and restrict plying of those vehicles which have no economic life to run on roads in the capital; shut down the illegal brick fields which are operating without license; stop burning of tyres and recycling of vehicles' batteries without approval; ensure that all the market owners or shopkeepers keep their garbage in bags and the city corporations to remove those after the shops or markets are closed; stop waste burning where and there; use improved cooking stoves and fuel in slum areas.

Mid-term: Suction trucks can be used to cleaning the road and collect road dust; mandatory introduction of separated bicycle lanes; providing adequate mechanical ventilation inside the house to control indoor air pollution; more tree plantation is needed; encourage rooftop gardens to increase green cover and reduce city temperature; conserve urban wetlands and water reservoirs; install high-tech brick kilns; increase the use of blocks; use of cleaner fuel; improved traffic management; introducing air pollution forecasting; establishing more cams; include air pollution in the textbook; crating more awareness through print and electric media.

Long-term-(Policy related): Separate plans to prevent air pollution in the dry season (November, December, January and February); introduce separate air pollution control commission; approved and implement the Clean Air Act 2019 as soon as possible; coordinate development activities through the introduction of city governance; include environmental cadres in the Public Service Commission (BCS); encouraging public transport and discouragement of private cars; start using advanced technology incinerators in waste management and generate energy from waste; stop building new Coal Fire Plant (CFPs) for power generation; do more research on air pollution including trans-boundary air pollution; gradually replacing the burnt bricks; north south alignments for building rows; stringent emissions standards for coal fired power plants; artificial rain can be introduced in dry season and increasing budget for DoE.

Conclusion

Although the air pollution situation in Dhaka has improved during COVID-19, it was only short-term. Once the coronavirus is under control, the ongoing lockdown in Dhaka will be lifted. Numerous students, job holders, workers and businessmen will join the workplace. As a result of coronavirus no doubt, various serious economic, social, political, mental health, educational and environmental crises are imminent in Bangladesh and all over the world. As a result, on the one hand, some people in the city who have lost their jobs will be forced to flee to the villages; on the other hand, innumerable temporary workers will leave the villages and flock to Dhaka in groups in the hope of earning an income. Dhaka will get back that old image of dust, traffic jams and pollution. Learning from this situation in Corona requires sincere planning and determination of people to save lives and nature. If air pollution is prevented, we can leave a livable city for the next generation. This will increase the average life expectancy of more than a year. It can play a role in preventing climate change. People will be mostly free from disease. Visit to doctors will reduce. People's medical expenses will be reduced. Work capacity and working hours will increase. People's financial well-being will increase. Prosperity will come in GDP. We do not have to wait for any untoward epidemic to improve our air quality, one day Dhaka will rise to the top of the list of livable cities in the world.

Professor Dr. Ahmad Kamruzzaman Majumder, Dean, Faculty of Science, Chairman, Department of Environmental Science, Stamford University Bangladesh, Founder and Director, Center for Atmospheric Pollution Studies (CAPS) and Joint Secretary, Bangladesh Poribesh Andolon (BAPA), E-mail: dk@stamforduniversity.edu.bd)