The word “Smog” was first used in the early 20th century and was originally named for the mixture of smoke and fog in the air. It is a type of intense air pollution and refers to smoky fog[1]. Smog is a condition of severe air pollution resulting mainly from anthropogenic sources including vehicular emissions, coal combustion emissions, forest and agricultural fires, industrial emissions, and photochemical reactions of these emissions.

Smog is often categorized as being either summer smog or winter smog. Summer smog is an air pollution episode that occurs during hot weather and is basically linked with the  photochemical formation of ozone. It is formed when nitrogen dioxide reacts with hydrocarbons in the presence of sunlight and forms ozone, which can then be mixed with particles. Winter smog on the other hand is formed when a thin layer of the atmosphere near the earth becomes cooler as a result of thermal inversion than that above it. Cold air is heavier than warm air, so temperature inversion limits its vertical mixing and it traps pollutants near the surface of Earth. These conditions often occur at night and during winter season[2].  The cold air is heavier than the warm air above it and it results in temperature inversion. The temperature inversion limit vertical mixing and resultantly pollutants are trapped at ground level. This condition persists until sunlight removes the temperature inversion or there is an event of rainfall. The air pollution of some of the most polluted cities i.e. Beijing, Mexico City, Los Angeles, Delhi, Tehran, Lahore and other cities often increases due to temperature inversion that traps pollutants close to the ground surface.

Both primary and secondary pollutants contribute to the formation of Smog. Pollutants that are directly emitted from a source are primary pollutants e.g. sulphur dioxide whereas those that are produced as a result of chemical reactions of primary pollutants in the atmosphere e.g. ozone are known as secondary pollutants.

The main sources of smog are coal and transportation emissions. Coal fires used previously to heat individual buildings and provide energy in power plants can emit significant amount of smoke that contribute to the formation of winter smog. Apart from this, a more important and significant source contributing to formation of smog is emissions from buses, trucks and automobiles. Exhaust emissions from the vehicles contain a number of harmful gases including carbon monoxide (CO), nitrogen oxides (NO and NOX), volatile organic compounds and hydrocarbons. Transportation emissions also contain comparatively small amounts of sulphur dioxides and particulate matters. The nitrogen oxides and volatile organic matters can undergo a number of chemical reactions with heat, sunlight, moisture, ammonia and other compounds to form the ground level ozone, noxious vapors and other particles that result in smog formation. Other anthropogenic activities that aggravate the severity of smog  are stubble burning in neighboring agricultural areas and emissions from brick kilns operating on olden technology.

Smog is toxic in nature and can have severe impacts on human health. It results in nose, eye and throat irritation, watery eyes, inflames breathing passages and causes difficulty in breathing, causes wheezing, coughing, a shortened life-span and premature death. It is harmful particularly for elders, children and patients having heart and lung problems e.g. bronchitis, asthma and emphysema.

Lahore Smog is a burning topic nowadays. The first episode of winter smog in Lahore occurred in 2016 and was initially mistaken as fog. However, it had an acrid burning smell and was irritating to the nose, eyes and throat. Thus, it was soon identified as a pollution problem. In 2017, after a number of petitions were filed by citizens against the concerned government departments and the Environment Protection Authority (EPA), the Lahore High Court (LHC) ordered the formation of a smog commission to look into the sources that caused this catastrophic air pollution and its possible mitigation measures. The commission released its report in May 2018, and it was suggested that there was a dire need for immediate actions to prevent reemergence of smog in winter. Industrial emissions, car fumes, smoke from brick kilns, residue from crop and rubbish burning in nearby fields, and dust from the construction sites were some of the reasons identified as potential causes of the smog in Lahore that created extremely hazardous situation in the capital. Recommendations from the Smog Commission to prevent smog included shutting down brick kilns that failed to use fuel-efficient technology, fining polluting vehicles and farmers burning rice stubble in the winter and curbing emissions from factories. The commission also ordered the planting of trees in urban areas and efforts to spread environmental awareness in schools.[3]

However, since then, Lahore has faced a total of 4 winter smog episodes and the government and environmental bodies are still unable to prevent it. Lahore again faced a severe smog cloud just at the start of winter this year. Its air quality dropped so much on the evening of 6 November 2019 that AQI values of 600-800 i.e. double the safety limits were recorded in parts of the city.  

Air Quality Index or AQI is a measure of the quality of air over a particular area. The AQI is a scale from 0 to 500.  As the AQI value rises, air pollution levels also increase, and the health concerns become more serious.[4] The threshold for ‘hazardous’ level of air quality is AQI 300.

AQI values vary for different countries depending upon their national air quality standards. In Pakistan, AQI ranging from 0–50 (Level 1) is considered excellent.  There are no negative health effects and outdoor activities can be continued normally. An AQI of 51–100 (Level 2) is considered good and some pollutants may slightly affect very few hypersensitive individuals. Only very few hypersensitive people should reduce outdoor activities. An AQI of 101–150 (Level 3) is deemed slightly polluted and healthy people may experience light irritations. However, sensitive individuals will be slightly affected to a larger extent. Children, seniors and individuals with respiratory or heart diseases should reduce sustained and high-intensity outdoor exercises. An AQI of 151–200 (Level 4) is a case of moderate pollution. Sensitive individuals will experience more serious conditions. The hearts and respiratory systems of healthy people may be affected. In these circumstances, children, elderly and individuals with respiratory or heart diseases should avoid sustained and high-intensity outdoor exercises. General population should moderately reduce outdoor activities. An AQI of 201–300 (Level 5) is deemed to be a case of heavy pollution. Healthy people will commonly show symptoms. People with respiratory or heart diseases will be significantly affected and will experience reduced endurance in activities. Children, seniors and individuals with heart or lung diseases should stay indoors and avoid outdoor activities. General population should reduce outdoor activities. An AQI of 300 and beyond (Level 6) means the air quality of a particular area is severely polluted. Healthy people will experience reduced endurance in activities and may also show noticeably strong symptoms. Other illnesses may be triggered in healthy people. Elders and the sick should remain indoors and avoid exercise. Healthy individuals should avoid outdoor activities.[5]

In the month of October 2019, relevant Pakistani organizations and departments recorded an AQI of as high as 484 in Lahore which fell into the category of Level 6 and the conditions were severely polluted.

Health experts have issued a number of preventive measures for the general public that should be exercised as long as the smog persists. According to them, the elderly, children and the infirm should stay indoors with their windows closed, people who feel the effects of smog should drink plenty of water and cover their faces with mask or handkerchief if they have to travel outside, in case of smog levels reaching hazardous levels people should stay in their homes and avoid any kind of outdoor activities, air purifiers should be used inside the houses, in case of situations where outdoor activities can’t be avoided people should wear N95 face mask that helps in reducing the inhaling of toxins.

A scale called PM2.5 scale is used to measure the quality of air. PM2.5 refers to atmospheric particulate matter (PM) that has a diameter of less than 2.5 micrometers. Higher the value on PM2.5 scale, higher is the pollution level and greater will be the health effects.

The air quality of Lahore is very bad, and it worsens as winter approaches. It is so bad that The World Economic Forum even went so far as to say that “some days, Lahore has the worst quality of air in the world”. According to rankings released by the World AQI, Lahore was ranked the second most polluted city on October 29. Indian capital New Delhi ranked first with an average concentration of fine particulate matter at 373 AQI, followed by Lahore at 188 AQI in cubic metre of air. Earlier, the Punjab provincial capital was briefly ranked first in the list of most polluted cities[6]. Pakistan, Mongolia and Egypt are among the most polluted countries according to the 2018 World Air Quality Report[7].

The government has taken a number of preventive measures and legal actions against parties who contributed largely to pollution. It has forced brick kiln owners to shift to a cleaner technology e.g. zig-zag technology, offered easy loans to the owners to enable them to make the switch and also fined the kilns that operated using the dirtiest technologies, such as burning used tires. A large number of cars and generators in Pakistan rely on diesel which is a major producer of hazardous emissions. Completely moving to an alternative cleaner fuel may reduce the problem by manifolds. Thus, we need to adopt a holistic approach to air pollution control by changing the way we live and controlling air pollution sources at individual level.


[1] https://www.sciencedaily.com/terms/smog.htm

[2] http://www.learner.org/courses/envsci/unit/pdfs/textbook.pdf

[3] https://www.reuters.com/article/us-pakistan-smog-lahore/as-lahore-chokes-on-winter-smog-pakistan-moves-to-cut-air-pollution-idUSKCN1P10XS

[4] http://geospatialhealth.net/index.php/gh/article/download/442/397

[5] https://www.thenews.com.pk/latest/552140-smog-in-lahore-turns-citys-air-quality-worst-in-the-world

[6] https://www.thenews.com.pk/latest/552140-smog-in-lahore-turns-citys-air-quality-worst-in-the-world

[7] https://www.telegraph.co.uk/travel/destinations/asia/india/articles/delhi-most-polluted-city-in-the-world/