Dhaka, the densely populated capital of Bangladesh,  has once again topped the list of world cities with the worst air quality. The capital's Air Quality Index (AQI) score was recorded at 288 at 9am on Monday. Pakistan’s Lahore and Afghanistan’s Kabul occupied the next two spots, with AQI scores of 255 and 211, respectively. Read: Air Pollution: Dhaka ranks 2nd worst, Lahore tops list An AQI between 201 and 300 is said to be 'poor', while a reading of 301 to 400 is considered 'hazardous', posing serious health risks to residents. 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 AQI is based on five criteria pollutants -- Particulate Matter (PM10 and PM2.5), NO2, CO, SO2 and Ozone. Dhaka has long been grappling with air pollution issues. Its air quality usually turns unhealthy during winter and improves during monsoon. A report by the Department of Environment (DoE) and the World Bank in March 2019 pointed out that the three main sources of air pollution in Dhaka "are brick kilns, fumes from vehicles and dust from construction sites". Read:Downpour downs pollution levels in Dhaka With the advent of winter, the city’s air quality starts deteriorating sharply due to the massive discharge of pollutant particles from construction works, rundown roads, brick kilns and other sources. 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. 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.