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. Delhi holds the top spot, with an AQI of 556 recorded on Wednesday.

Read: No, India is not responsible for Punjab’s smog. Here’s what’s really happening

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.

This chart shows different AQI categories and their effects on the population. — Courtesy AirNow.gov

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 horizon from November to February. Government officials blame the smog on crop burnings in India. Experts, however, say that the situation is caused by pollution in the country.

The situation has worsened this year, as the Punjab government, for the first time, announced the closure of schools due to dense smog. Residents accuse the government of taking insufficient measures to control the situation even as the administration insists that it is making efforts to deal with the smog.

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

Adviser to Prime Minister on Climate Change Malik Amin Aslam, earlier this month, said Pakistan has taken measures to stop crops stubble burning, a major cause of the phenomenon, and other countries should also come forward to address it.

He said that two smog checking units had been installed in Lahore and his department was also focusing on measures to increase resources to address the issue.

"With the help of the World Bank the government was launching a programme to address the air quality issue," he said.

The adviser said the smog level in India was increasing but the Pakistani government had taken measures to reduce it here. He pledged that Lahore would be made “smog free”.

Karachi is the seventh most polluted city in the world with an AQI of 167 and is classified as 'unhealthy'. AQI recorded between 151-200 is classified as 'unhealthy' and the air quality may cause the entire population to experience adverse effects. 'Sensitive groups', i.e., people with lung diseases, children and elderly people, will be at greater risk, according to Air Now.