The Punjab education department on Thursday decided to keep all public and private schools in Lahore, Gujranwala and Faisalabad closed on November 15 and 16 due to poor air quality.

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

Punjab Minister for Schools Education Dr Murad Raas in a tweet vowed that the government will protect school-going children at all costs. "The Punjab government is taking all necessary steps to improve air quality," he added.

On Wednesday, the provincial education department had prohibited holding all outdoor activities in all 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 second time in a month that the government has decided to keep schools closed due to smog.

Lahore's air quality remained 'hazardous' with an air quality ranking of 447, according to Air Visual's Air Quality Index (AQI) list on Wednesday.

The Punjab capital is ranked the second most polluted city in the world, according to Air Visual, which records air pollution levels across the globe in real time. New Delhi holds the top spot, with an AQI of 556 recorded on Wednesday.

An AQI ranking between 301-500 (or above) is classified as 'hazardous' and would "trigger a health warning of emergency conditions. The entire population is more likely to be affected," according to Air Now.

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.