New Delhi: Pakistan blamed poor air quality this week on pollution drifting from neighbouring India, where firecrackers set off during the Hindu festival of Diwali over the weekend blanketed much of the north in toxic smog.The northern Pakistani city of Lahore topped Swiss group IQAir's ranking of the world's most polluted major cities for a second day on Tuesday, with an air quality index (AQI) of 263, categorised as "very unhealthy".