Mumbai became the second most polluted city among 109 places tracked by IQAir, a Swiss technology company measuring air quality in real-time.
The top 5 Cities in the world are:
Beijing
Mumbai
Karachi
Jerusalem
Shenyang
The air quality index (AQI) score is based on the US system where a score of between 0-50 is good, 51-100 is moderate, 101-150 is unhealthy for sensitive groups, 151-200 is unhealthy, 201-300 is very unhealthy and >301 is hazardous.