On Thursday, the capital slipped to the fourth position in the list of cities with the worst air quality in the world, with Kyrgyzstan’s Bishkek, Pakistan’s Karachi and India’s Delhi galloping past Dhaka to grab the first, second and third spots, respectively.

Dhaka's air quality index (AQI) at 10.18 am on Thursday read 241, considered 'poor' that is 'very unhealthy'. An AQI between 201 and 300 is considered 'poor', while a reading of 301 to 400 is said to be 'hazardous', posing serious health risks to city residents.

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The capital's poor air quality has become a serious cause of concern for residents as long-term exposure to air pollution has been linked to an increased risk of dying from Covid-19.

AQI, an index for reporting daily air quality, is used by government agencies to inform people how clean or polluted the air of a certain city is, and what associated health effects might be a concern for them.

In Bangladesh, the overall AQI is based on five criteria pollutants – Particulate Matter (PM10 and PM2.5), NO2, CO, SO2, and Ozone (O3).

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Bangladesh has a subtropical monsoon climate characterised by wide seasonal variations in rainfall, high temperatures and humidity. Generally, Dhaka’s air starts getting fresh when monsoon rains begin in mid-June. The air remains mostly acceptable from June to October.

In February last year, Bangladesh's Environment, Forests and Climate Change Minister Md Shahab Uddin admitted that air pollution levels in the capital "has reached an extreme level". "This is mainly due to uncontrolled discharge of dust from construction projects, smoke from vehicles and brick kilns," he told UNB.

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Besides, a report by the Department of Environment (DoE) and the World Bank in March 2019 also pointed out that the three main sources of air pollution in Dhaka "are brick kilns, fumes of vehicles and dust from construction sites".

Air pollution consistently ranks among the top risk factors for death and disability worldwide. Breathing polluted air has long been recognised as increasing a person’s chances of developing heart disease, chronic respiratory diseases, lung infections, and cancer, according to several studies.

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As per the World Health Organization (WHO), air pollution kills an estimated seven million people worldwide every year, largely as a result of increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.

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Over 80 percent living in urban areas which monitor air pollution are exposed to air quality levels that exceed WHO guideline limits, with low- and middle-income countries most at risk.