Global air quality monitors have placed Pakistan’s Lahore city as they second most polluted city in the world on Monday.

Switzerland-based, real-time air quality information platform, IQAir has ranked Delhi as the most polluted city in the world with an air quality index (AQI) of 656 by 2:45pm on Monday, which is categorised as “hazardous”.

Delhi was followed by Lahore that came in second with an AQI of 256 by 2:45 pm, which is categorized as very unhealthy. Lahore’s AQI was 434 in the morning, which is categorised as “hazardous”.

An AQI between 0 and 50 is considered good. While anything over 300 is “hazardous” and requires an emergency response. When the AQI exceeds, health experts advise people to avoid outdoor activities and to keep windows and doors closed.

The US Embassy — which also monitors air quality in major cities of Pakistan — has placed the AQI as high as 623 for Lahore in the morning that went down to 293 by the afternoon..

After Lahore, the second most polluted Pakistani city is Karachi with AQI of 108, the 19th most polluted in the world.

While US embassy puts Karachi’s AQI at 162 by afternoon. Smog has been a constant threat to Pakistan’s environment in recent years and cand be potentially dangerous in the wake of coronavirus pandemic.