Daily Times

The port city ranked the worst on a global Air Quality Index on Tuesday morning, placing atop the world’s most polluted cities.

It was closely followed by Indian capital Delhi and Kyrgyzstan capital city Bishkek. Karachi was ranked first on the Air Quality Index with 351 particulate matter in the morning.

AQI as high as 151-200 is considered unhealthy, while an AQI between 201 to 300 is more harmful and an AQI over 300 is dubbed extremely hazardous.

Around 11:00 am Tuesday morning, Karachi’s air was still harmful with its AQI at 231 and at this place after Bishkek with 347 AQI and Delhi 272. Lahore was at fourth rank on the index with 214 and Kabul was fifth with 203 particulate matter in the air.

Kolkata 194, Dhaka 189, Mumbai 177, Kathmandu 158 and Wuhan 158, were other five cities on the Air Quality Index.

According to experts, the air is 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, severely compromising air quality.

Though southwestern winds blowing from the sea 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, sulphur dioxide, and nitrogen dioxide.