Lahore and Karachi are among the ten most polluted cities in the world in terms of air quality, according to air quality monitor AirVisual India's New Delhi, Kolkata and Mumbai also feature in the list and occupy spots in the top 10.Smog is a perennial problem for citizens of Lahore. According to data released by Pakistan Air Quality Initiative (PAQI), the provincial capital recorded only two days of good air quality in 2017.Air pollution causes serious health problems, including respiratory failures, lung and heart diseases. It reduces life expectancy by 60 months and leads to almost 135,000 deaths every year, making it the leading cause of sickness in the country.In August, Lahore Division Commissioner Dr Mujtaba Piracha warned that it was time to adopt measures to fight smog as the season starts in October and continues till the end of December.The commissioner said Section 144 would be imposed on burning crop stubble. He said that crop burning, brick kilns, industries and traffic emissions were considered to be the main factors causing smog in Lahore and adjoining areas.Officials were directed to form district smog control committees comprising members from the environment, agriculture, industries and police departments to create awareness and sensitise farmers. Piracha also said brick kilns would remain closed from October 20 till the end of December to curb smog.