LAHORE: Lahore remained the second most polluted city in the world on Saturday, after New Delhi, despite multiple steps taken by the government for improving the air quality. Lahore remained the second worst city on the Air Quality Index in the world after Indian capital New Delhi, with the particulate matter measured at 303 in the morning. It is to be mentioned here that the level of the particulate matter in New Delhi measured 351 on the AQI. Bangladesh’s Dhaka remained third among the top, Kabul fourth and Karachi fifth on the Index with worst air quality. According to the reports of international media and a study of the United States National Aeronautics and Space Administration (NASA), burning of crop residue in northern Indian states causes a dangerous hike in environmental pollution in the region. 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 dubbed extremely hazardous. According to experts, 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 extremely dangerous levels, severely compromising the air quality. The AQI is calculated based on five categories of pollution: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide.