达卡的空气质量

How bad is the air pollution in Dhaka?

Dhaka, formerly known as Dacca, is the capital city of Bangladesh. It holds the title of not only being the largest city in the country, but being the 9^th largest city worldwide. It also ranks at 6^th place out of the most populous cities in the world, with just under 9 million people living within the city’s limits. Due to these reasons, as well as being the economic hub of the whole country, Dhaka is subject to some fairly bad pollution levels annually, with only brief periods of respite, that despite being lower still hold some relatively high numbers of pollution readings, making its air harmful to breathe year-round.

In 2019, Dhaka came in with a PM2.5 reading of 83.3 μg/m³ as the yearly average, putting it in the ‘unhealthy’ bracket of air quality, which requires a PM2.5 reading between 55.5 to 150.4 μg/m³ to be classed as unhealthy. Besides just being a classification, this rating is of course indicative that the air quality is indeed unhealthy to breathe, with numbers going well above the yearly average such as January coming in with a record high of 181.8 μg/m³, putting it into the ‘very unhealthy’ bracket (150.5 to 250.4 μg/m³).

This yearly average reading of 83.3 μg/m³ was enough to put Dhaka in 1^st place out of all cities in Bangladesh (of note is that the only city registered for pollution levels in the country was Dhaka, so this first-place ranking was inevitable) as well as being the 21^st most polluted city worldwide in 2019, making the level of air pollution in Dhaka quite severe, and of great detriment to its citizens.

What are the main causes of pollution in Dhaka?

Dhaka faces pollution problems from all sides, as being a highly populated city, it would be subject to the air contaminating effects of the massive use of cars, motorbikes and trucks, many of which are not subject to strict regulations in regards to the age or quality of their engines, or the fuels they run on. As a result, many of these vehicles travel the roads emitting far more pollution that a regular car would, often running on fossil fuels such as diesel, which releases higher levels of contaminants into the air than its cleaner counterparts.

There is also the industrial side of the city, contributing to the ever-growing pollution levels. Factory or production sites such as brick kilns are responsible for the massively elevated levels of pollution. Due to an economic boom and the subsequent increase in demand, Dhaka’s kilns are known to produce billions of bricks each year, often relying on unregulated fuel sources for power (such as the burning of coal, wood and any other combustible material) which can release excessive amounts of noxious fumes and smoke into the atmosphere.

Besides these two issues, there are problems related to large dust concentrations building up in the city, somewhat similar to the highly polluted city of Delhi in India, as well as open burning sites where refuse containing organic matter as well as toxic materials such as plastics and rubber are set alight in the streets.

What are the main pollutants found in the air in Dhaka?

With a large amount of its pollution coming from vehicles, industries and construction sites, Dhaka would be subject to some extremely dangerous pollutants finding themselves into its atmosphere. Materials such as black carbon and volatile organic compounds are all released in copious amounts from the use of fossil fuels such as diesel in coal, present in vehicles and factories alike, as well as arising from the aforementioned open burn sources (with the incomplete combustion of materials such as wood often leading to large amounts of black carbon being produced, often in the form of soot).

Chemical compounds such as nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) would also be abundant in the atmosphere, once again finding their creation from both cars and factories alike. The brick kilns would produce vast amounts of their own smoke and haze, containing other compounds such as carbon monoxide (CO) and ozone (O₃). The large amounts of dust given off by poorly maintained construction sites would contain a variety of PM2.5 and PM10, such as silica dust, or finely ground soil or gravel particles, all of which can cause a number of long-term health effects when respired.

When is pollution in Dhaka at its worse?

As touched on previously, pollution levels start to show considerable rises in the month of October, coinciding with the end of monsoon season and as such lacking the necessary rain that is always helpful in cleaning a cities air and washing away its fine dust particles.

September saw a PM2.5 reading of 37.7 μg/m³ in 2019. This jumped up significantly in October to 64.6 μg/m³, and increase of nearly twofold. These numbers continued to rise until they hit their absolute peak in January, with a reading of 181.8 μg/m³ being present.

With air pollution levels this bad, preventative measures become vital for Dhaka's citizens, with the avoidance of outdoor activities as well as the wearing of fine particle filtering masks being highly necessary. After the peak in January, pollution levels still remained extremely high but showed a steady drop, with a reading of 145.7 μg/m³ in February, followed by 107.4 μg/m³ in March. These numbers continued to drop until reaching the cleanest months of the year, June through to September, with August coming in with the cleanest reading of the year at 31.3 μg/m³.

What can Dhaka do to reduce its pollution levels?

In order to reduce such elevated levels of pollution, many steps would need to be taken, albeit in the face of such economic growth it would a task that the city of Dhaka would be hard pressed to do. The introduction of stricter regulations regarding fuels and vehicles allowed on the road would be helpful in the fight against reducing ambient pollution levels in the air, with the removal of diesel fuel as well as ancient fume producing engines being of large help.

Other steps would be to introduce stricter measures to both factories and construction sites, holding individual organizations accountable for the amount of pollution that they produce, with the possibility of adding fines to those that exceed unsafe levels of pollution, as well as particulate matter. Whilst certainly a compounded issue, the introduction of these initiatives would be a step in the right direction for Dhaka to obtain a cleaner level of air quality, and improve its US AQI readings as well as PM2.5 levels.