Smog, also known as ground-level ozone, is a thick yellowish black fog which suspends in the air.
It is caused when air pollution, emissions and fumes combine with fog and sunlight, forming a thick layer of smoke-like film in the atmosphere. According to experts, emissions from industries and vehicles and cutting of trees worsen the phenomenon.
The Met Office has released a weather warning describing the smog — comprising nitrogen oxide, carbon monoxide, sulphur dioxide and other aerosols — as a result of cold high pressure in the upper atmosphere. Suspended matter accumulates in the lower atmosphere, colliding with water vapour which causes a chain reaction that produces smog.
The Met Office has warned the smog is likely to persist for the next two or three days in Lahore, Islamabad, Rawalpindi, Jhelum, Gujranwala, Faisalabad, Okara, Sahiwal, Pakpattan, Multan and Khanewal districts.
People may experience short-term skin and respiratory conditions such as eye irritation, coughing, throat/chest irritation and skin irritation. Road and air traffic could be affected due to low visibility, the Met Office said.
Health experts recommend artificial tears for eyes as one way of dealing with smog. The public is advised to adopt preventative measures such as avoiding the outdoors and using face masks when going out.