Lahore ranked first in the list of most polluted cities in the world, while Indian capital city New Delhi remained second and Kolkata ranked third in the AQI list. According to the Air Quality Index, Lahore has been ranked first in the list with 453 reading. Fog engulfed Lahore’s Allama Iqbal International Airport and poor visibility affected flight operations. Most incoming flights were diverted to Islamabad, Airport Manager said. “International flight QR 628, coming from Doha to Lahore, was also diverted to Islamabad,” airport official said. “Flight operations will be brought to normal routine after improvement in the visibility,” he added. According to the reports of international media, burning of crop residue and garbage in northern Indian states causes dangerous hike in environmental pollution in the region. The AQI is calculated on the basis of five categories of pollution: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. AQI as high as 151-200 is considered unhealthy, while an AQI rating between 201 to 300 is more harmful and AQI over 300 is termed extremely toxic. According to experts, increase in air pollution used to be recorded in the winter. A change in the wind speed, wind direction and sliding minimum temperature increases air pollution. 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 a city. The smoke produced by burning crop remnants, factories and 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 to extremely dangerous levels, severely compromising the air quality.