Lahore ranked first and Karachi second most polluted city on the Air Quality Index (AQI).

Pakistan’s two biggest cities have got the dubious distinction of soaring to first and 2nd from the top in the most polluted cities of the world on the air pollution measurement scale.

Lahore was measured to have 414 hazardous particulate matter in the air and Karachi 215 hazardous substance, according to the air quality index.

Kolkata in India has been third from top in the AQI with 189 reading of hazardous particulate matter in the air.

It is to be mentioned here that AQI as high as 151-200 is considered unhealthy, while an AQI reading between 201 to 300 is more harmful and AQI rate over 300 mark is extremely hazardous.

According to experts, the air becomes heavier in the winter as compared to summer, causing poisonous particles in the atmosphere to move downwards and making it polluted. As a result, a layer of polluted particles, including large amounts of carbon and smoke, engulfs a city.

The smoke produced by factories and by burning coal, garbage, oil or tyres enter the atmosphere and the impact of it appears at the onset of winter and remains till the season’s end, experts said.

Thus, air pollution reaches to extremely dangerous levels in cold weather, severely compromising air quality.

Although southwestern winds blowing from the sea in Karachi may work as a filter for the air, these winds remain mostly suspended during the winter, according to experts.

They noted that winds blowing from the northeast increase the concentration of hidden polluted particles, and a healthy atmosphere in such a situation is subject to rainfall, which washes off all polluted particles.

The AQI calculation is based on five categories of pollution: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide.