KARACHI: Lahore ranked fourth and Karachi at 10th on a global Air Quality Index (AQI) on Saturday, among the world’s most polluted cities, ARY News reported.

In Pakistan’s cities, Bahawalpur was measured to have 327 hazardous particulate matter, while the reading of Lahore was 194, Rawalpindi 189, Raiwind 170, Karachi 167, and Multan 165, according to the air quality index.

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 over 300 marks is dubbed 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 the atmosphere polluted. As a result, a layer of polluted particles, including large amounts of carbon and smoke, covers the city.

The smoke produced by factories and by burning coal, garbage, oil or tyres enters the atmosphere and the effects of this appear at the onset of winter and remain till the season’s end, experts said.

Thus, air pollution reaches 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 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 is calculated based on five categories of pollution: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

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