Winter Air Pollution in Bangladesh: Breathing Through the Gray Haze

When the cold season hits Bangladesh in November-February every winter, the skies in Dhaka, Chattogram, Narayanganj, Gazipur and other large cities of the country appear perfectly familiar and at the same time terribly threatening. The cityscape is regularly blanketed with a heavy and gray blanket. It might seem to the careless eye an air of mist or fog, but this haze of seasonal fog is much darker. It is smog, a heavy layer of air pollutants that suffocates millions of people and bewitches Bangladesh to be one of the most polluted countries in the globe in winter. The core of this crisis is the presence of fine particulate material or PM2.5 or microscopic particles, measuring 2.5 micrometers in diameter, and PM10 and a combination of gaseous pollutants, forming a toxic air cocktail that is extremely dangerous to human health. 

The quality of air in Bangladesh is determined by Air Quality Index, or AQI. A score below 50 is good whereas a score above 200 depicts very unhealthy conditions and above 300 would be dangerous. In winter, AQI in Dhaka and other cities will often be much higher than 250, occasionally even reaching 300. One very cold morning in December, Dhaka registered an AQI of 296 and thus became the country with the worst air quality in the world at that time. Bangladesh was considered as one of the top three countries worldwide in terms of long-term PM2.5 emissions and the average was significantly higher than the safe level of 5 micrograms per cubic meter by the World Health Organization. These figures are not just statistics, but the life of millions of people who breathe poisonous air every day. 

Natural atmospheric processes as well as human activities contribute to the seasonal increased pollution. Temperature inversion is one of the major natural processes that cause the same. Warmer air at the ground level in normal weather conditions ascends and the pollutants are distributed in the atmosphere. Cold air however gathers along the surface during winter and a layer of warmer air gathers on top making the pollutants practically ground trapped. This inversion layer serves as a lid, which does not allow the smoke, dust and chemical particles to ascend. The stranded pollutants accumulate, taking days and occasionally weeks and winter is the most polluted season in the country. 

This is worsened when it comes to the meteorological conditions during winter. The wind is normally slow, which minimizes the motion of air horizontally that may sweep away pollutants. The quantity of rainfall is low, as compared to the monsoon season, which is characterized by abundant rains that wash the pollutants off the atmosphere. The air is dry over long durations, which means that dust, smoke, and fine particles are unable to be washed off. A combination of all these natural conditions forms the ideal environment where smog can develop and exist, making winter skies a visual and health hazard. 

Winter air crisis is further aggravated by human activities. The Bangladesh brick industry, which is one of the largest industries in South Asia is at full capacity during the dry season as the only time that they can produce completely is when it is dry. A vast number of brick kilns still operate using old technology, which consists of burning coal, wood, rubber, and low quality fuel producing huge quantities of soot, sulfur dioxide, and heavy metals into the atmosphere. It has been shown that in regions around Dhaka, during winter months, it is the contribution of the brick kiln to more than half of the total PM2.5 pollution. 

Another important contributor is construction activity. During the winter the roads, flyovers, bridges, and residential buildings are being built at a rapid rate and causing clouds of dust to be released into the air. Crude particles, primarily PM10, are stirred by unpaved roads, bare building materials, and the move of vehicles, and, though larger than PM2.5, are sufficiently small enough to cause irritation to the lungs, eyes and throats. Traffic jam, a problem that already exists on year round basis in cities, is only enhanced during winter. Nitrogen oxides and black carbon released by diesel buses, trucks and poorly maintained vehicles are compounded with stagnant winter air to increase pollution. Cooking with crop residues and fire wood contributes to the level of pollution in rural and peri-urban places, proving that it is not only an urban problem but a national one. 

The most harmful of airborne particles are PM2.5 that can enter deep into the lungs and reach the bloodstream. When absorbed into the body, the particles cause inflammation, organ dysfunction, and risk of asthma, chronic bronchitis, heart attacks, strokes, and premature death. Dhaka has recorded winter PM 2.5 levels of more than 200 micrograms per cubic meter, forty times more than the safe limit set by the WHO. Although PM10 is not very harmful in the perspective of penetrating deep into the lung, it is still harmful in causing respiratory irritation, particularly to the children and aged. PM2.5 and PM10 pose a twofold danger together as they have become a daily problem when it comes to breathing in winter. The pollutants finally get settled by a process known as deposition, but it takes place in two ways; the dry way and the wet way. During dry deposition particles and gases settle on surfaces (buildings, trees, and soil) through the force of gravity or stickiness. Due to the lack of or minimal rainfall in winter dry deposition is prevalent and the pollutants are frequently blown back into the atmosphere by the wind, or vehicles passing by. Wet deposition takes place when pollutants are washed away in the atmosphere through rain hence cleaning the air. This is what makes the quality of air in the monsoon season to be excellent in that it cleans the atmosphere and most of the dust and chemical substances that are in the atmosphere are washed away by the rainfall, which prevails during the dry winter months. The chemical composition of winter air pollution is complex. Nitrogen oxides from vehicles and industrial sources react in sunlight to form ground-level ozone, which damages lung tissue and reduces crop yields. Sulfur dioxide from burning high-sulfur fuels irritates the respiratory system and contributes to acid rain. Carbon monoxide produced by incomplete combustion reduces the oxygen-carrying capacity of the blood, putting people with heart conditions at serious risk. Volatile organic compounds from paints, solvents, and chemical industries react in the atmosphere to create photochemical smog, further worsening winter air quality. Together, these pollutants push the Air Quality Index into the “Unhealthy” or “Hazardous” range, especially in January and February, when smog is thickest. 

The impacts of winter pollution are both the short run and the long run consequences. Research has approximated that more than 80,000 premature deaths in Bangladesh are caused by air pollution annually. Hospitals are reporting increases in patients with respiratory and cardiovascular complications during the winter, and children experience poor lung development as well as elderly people experience chronic difficulty in breathing. The price is astronomical economically. Air pollution lowers productivity, expenditure on health care, and agricultural output, and the total cost is estimated at over four percent of the Bangladesh annual GDP. 

The government has responded to this crisis by closing down illegal brick kilns, encouraging cleaner kiln technologies such as Hybrid Hoffman Kilns and Tunnel Kilns, introduction of Euro IV fuel standards, and encouraging the use of compressed natural gas vehicles. Networks of air quality measures are on the rise and a draft Clean Air Act will be developed to establish a tougher regulatory framework that can govern emissions control. Nonetheless, there is still an unequal enforcement, uncontrolled urbanization, and still, the waste management is quite poor that negates the way. 

Scholars concur that it is necessary to change the system to make any meaningful improvement. Switching to renewable energy, increasing the use of effective public transport, strengthening the requirements of vehicles in pollution, and regional cooperation in transboundary pollution are necessary measures. It is also vital to create awareness among people in order to make them realize that the gray haze is not a natural and inevitable phenomenon but a crisis that can be prevented, and that is caused by human beings. 

Bangladesh is in a dangerous intersection. The seasonal haze, which used to be the harmless element of winter, has turned into a tangible manifestation of industrial excess, city abandonment, and lack of any policy. The cost of polluted air will keep increasing unless actions are taken drastically as the economy of the country grows. Clean air is not an extra, it is a basic human right. It will have to take political will, scientific vigilance and involvement of the population. Until that time every inhalation in the winter months will be the mute yet powerful threat floating silently in the grey skies of Bangladesh.