The Punjab education department on Thursday decided to keep all public and private schools in Lahore, Gujranwala and Faisalabad closed on November 22 due to poor air quality.

According to a notification issued by the provincial government, the schools will remain closed on Friday due to "dense smog" in the three districts.

Earlier this month, the Punjab education department had prohibited holding all outdoor activities in public and private schools across the province till December 20 for the same reason.

The government had directed all students to wear air filter masks during school hours. It had also decided to hold awareness sessions on environment in all schools. This is for the third time in a month that the government has decided to keep schools closed due to smog.

Lahore's air quality remained 'very unhealthy' with an air quality ranking of 245 on Thursday evening, according to Air Visual's Air Quality Index (AQI).

The Punjab capital was ranked the most polluted city in the world on Thursday, according to Air Visual, which records air pollution levels across the globe in real time.

For the last four years, smog, rightly being called the fifth season of Lahore, has deprived the people of sunshine and dusk-hour charm as layers of toxic smoke engulf the horizon from November to February. The situation has worsened this year.

Earlier this month, a group of students petitioned the Lahore High Court seeking a change in the AQI measurement system, and implementation of the Smog Policy.