Skip to content
Saans
اردو

Smog season

Smog season explained: why Lahore chokes every winter

Last reviewed 4 Nov 2026 · DanixSoft

Smog is air pollution, mostly fine particles (PM2.5), trapped near the ground with haze or fog. In Punjab it builds from late October and can last into January: cold nights create a layer of warm air above cooler air at the surface (an inversion), winds are light, and smoke from traffic, industry, brick kilns and burning crop residue and rubbish has nowhere to go.

Why it gets trapped

On a normal day, air warmed by the ground rises and carries pollution up and away. On long, clear winter nights the ground cools quickly, the air touching it gets colder than the air above, and that colder, heavier layer stays put. Pollution released into it builds up hour after hour until the sun warms the ground enough to mix the air again, usually in the early afternoon.

Light winds, high humidity and fog make it worse: particles grow in damp air and the fog itself lingers. A good spell of rain or a strong wind is what usually clears it.

Where the pollution comes from

Estimates of how much each source contributes differ between studies and between cities, so Saans does not quote one split as settled.

  • Vehicles: exhaust from cars, motorcycles, rickshaws, buses and trucks, plus road dust.
  • Industry and power generation, including diesel generators.
  • Brick kilns, especially older designs.
  • Burning crop residue after the rice harvest (October–November), in Pakistani and Indian Punjab, and burning rubbish.
  • Construction dust and household burning of wood or coal.

What it does to health

Fine particles reach deep into the lungs and the bloodstream. In the short term they cause coughing, sore throats, stinging eyes and asthma attacks, and they strain the heart. Over years, exposure raises the risk of heart disease, stroke, lung disease and lung cancer (WHO). Children, older people, pregnant women and people with asthma, heart or lung conditions feel it first.

How to protect yourself

  • Check the hourly forecast and do outdoor things at the cleanest time of day.
  • Wear a well-fitted N95, KN95 or FFP2 outdoors when the AQI is above 150 (see the mask guide).
  • Keep windows shut on bad days and run a HEPA purifier in the bedroom (see the purifier guide).
  • Move exercise indoors above AQI 150, and keep inhalers and medicines at hand.
  • Follow official notices on school timings and closures: Saans links to them on the advisories page.

How you can add less to it

  • Never burn rubbish or leaves.
  • Keep your vehicle tuned and tyres right; share rides on bad days.
  • Report open burning to the Environment Protection Department, Punjab.

Questions people ask

When does smog season start and end in Lahore?

It usually starts in late October, peaks in November and December, and eases by February as nights warm up and winds and rain return. The 5-day forecast on the Lahore page shows the days ahead.

Is smog the same as fog?

No. Fog is water droplets and is harmless. Smog is pollution; in winter the two often come together, and the fog keeps the pollution near the ground.

Does rain clear the smog?

A good spell of rain washes particles out of the air and usually brings the AQI down for a day or more. Light drizzle does little.

Why is the smog worse at night?

At night the ground cools, the air near it stops rising, and pollution collects in a shallow layer. The sun breaks that layer up during the day, so afternoons are often cleaner.