Introduction -
“Smog” was used to describe the combination of smoke and fog in 1911 by Dr. Harold Des Voeux.
Smog is a form of outdoor pollution. The term was originally used to describe a combination of smoke, fog, and chemical pollutants that poisoned the air in industrialised cities like London. Now the term refers to the effects of air pollution not necessarily associated with smoke particles. It is used to describe air pollution that is localised in urban areas, where it reduces visibility.
Formation of smog is affected by local meteorological conditions, like wind speed, direction and temperature. For example, during the winter months when wind speeds are low, it helps the smoke and fog to stagnate at lower levels of the troposphere in the northern regions of India.
Types of Smog -
Smog is the combination of various gases with water vapour and fine particles. Smoke particles get trapped in the fog giving it a yellow/black colour. This smog settles over cities for many days.
There are two different types of smog.
1. London Smog or Sulphurous Smog.London Smog -
Burning coal leads to emissions of Carbon dioxide, Sulphur dioxide and dust. When these pollutants mix with fog, droplets of highly corrosive Sulphuric Acid are produced in the air, and then London smog is formed. It occurs at very cold temperatures. In 1952, about 4,000 deaths were caused in Londor due to yellow fog. It lasted for 5 Days. This was called the Great London Smog.
In 1952, there was cold weather and windless conditions. Low-grade coals were burnt. This increased the amount of sulphur dioxide in the smoke. Air pollutants formed a thick layer of smog over the city. Due to the smog, people could not see anything to a distance of a few yards. Respiratory diseases and lung function disorders were caused due to this smog.
Effects of London Smog -
London Smog was the worst pollution-based fog in the city’s history.
- About 4,000 people have died as a result of the fog.
- Visibility was so impaired in some parts of London that pedestrians were unable to see their own feet.
- Ambulance services suffered and people found their own way to hospitals in the smog.
- Many people simply left their cars on the road.
- Indoor plays and many concerts were cancelled for this smog.
Though the fog lasted five days the effects of the smog were long-lasting. Many people were hospitalised due to pneumonia and bronchitis.
Photochemical smog -
This smog is produced when sunlight acts upon motor vehicle exhaust gases such as nitrogen oxides (NOx) and volatile organic compounds (VOCs).
VOCs + NOx + Sunlight → Photochemical smog
Ozone, aldehydes, nitrogen oxides, peroxyacetyl nitrates (PAN), and volatile organic compounds are the main components of photochemical smog.
Effects of photochemical smog
- Ozone is the main component of photochemical smog. It is a powerful oxidising gas. It attacks our tissues. It causes sore throats, inflammation, discharges in nasal passages etc.
- Ozone affects lung function and the lower respiratory tract.
- Ozone also attacks plants mainly citrus fruits, potatoes, legumes, soya beans etc.
- Other photochemical smog components and ozone cause damage to buildings and degrades rubber, clothing etc.
- Peroxybenzoyl nitrate produced in photochemical smog is 100 times more toxic than PAN.
Photochemical smog can be seen as a hazy shroud on warm days in congested cities. It is an irritant to humans and very toxic to plants. In developing countries, leaded fuel, old engines, industrial emissions, and fuelwood burning combine to create severe smog.
In developing countries, leaded fuel, old engines, industrial emissions, and fuelwood burning combine to create severe smog.
Urban Heat Island Effect -
Crowded urban areas (such as business districts) are warmer than the rural areas surrounding the city. We call such areas urban heat islands and they result from the following causes:
- The dark and tall buildings and the asphalt roads absorb a significant amount of light and radiation and emit it as heat, warming the city area.
- The lack of trees and other vegetation prevents evaporative cooling that occurs in other green areas.
- Waste heat from vehicles, air conditioners, and generators releases heat into the air.
Urban heat islands often have lower air quality because, along with the heat, there are also pollutants being pumped into the air. These pollutants are blocked from scattering and becoming less toxic by the buildings, roads, sidewalks, and parking lots. High- reflectivity coatings, green roofs, eco-friendly architecture, pedestrian-only areas, and other such measures can help reduce the heat island effect, but it is difficult to eliminate it completely.
Particulate Matter -
It is a varying mixture of particles (solid or liquid) less than 10mm suspended in air. Mining, construction, agriculture, vehicles, volcanic eruptions etc. add considerable particulates into the atmosphere. Some of these are visible as smoke, soot or dust; while others may not be easily visible. Of particulate concern are PM 2.5 and PM 10 as these can be easily inhaled into the lungs and can be absorbed into the bloodstream. Such particulate matter is called Respirable Particulate Matter.
Photochemical Pollutants - These are produced when sunlight starts complex chemical reactions among NOx, VOCs and other components of air. Different types of photochemical pollutants can be formed through these reactions which can be summarised as:
VOCs+ NOx+ Sunlight = Photochemical Pollutant
These can cause irritation of the eyes, lungs and other mucous membranes in humans and the rest of animal life. In plants, it causes stunted growth and death.
Sulphates and Nitrates - These are the most significant particulate pollutants. These are secondary atmospheric pollutants produced through chemical reactions between atmospheric compounds and sulphur dioxide and nitrogen oxides.
Harmful Effects of Smog on Human Health -
Smog can have hazardous health impacts. it may cause the following harmful effects on humans -
- Minor exposure to smog can cause eye irritation,
- It causes inflammation of lung tissue thus aggravating asthma and breathing difficulties.
- Ground-level ozone in the smog inhibits plant growth and causes immense damage to crops and forests.
- Photochemical smog components attack our tissues. It causes sore throats, inflammation, discharges in nasal passages etc.
Control Smog in the Environment -
Everyone can do their duty to reduce smog by changing their behavioural pattern such as
- Reduce or eliminate fireplace and wood stove use.
- Plant more trees to reduce air pollution.
- Complete fuel combustion in vehicles is very important. It decreases the formation of pollutants. This is done by developing exhaust system reactors in vehicles.
- Lead-free petrol is used in modern cars to decrease pollutants.
- In industries, gravity settling chambers, cyclone separators, venturi scrubbers, baghouses and electrostatic precipitators are used to remove the particulate matter.
- Internal combustion engines have been replaced by pollution-free power sources, e.g. solar cars. This greatly decreases the pollution.
Frequently Asked Questions (FAQs) -
Question - What is Smog?
Answer - Smog is a form of outdoor pollution. The term was originally used to describe a combination of smoke, fog, and chemical pollutants that poisoned the air in industrialised cities like London. Now the term refers to the effects of air pollution not necessarily associated with smoke particles. It is used to describe air pollution that is localised in urban areas, where it reduces visibility.
Question - What are the two types of song?
Answer - There are two different types of smog.
1. London Smog or Sulphurous Somg (Gray Air).
2. Los Angeles Type or Photochemical Smog (Brown Air).
Question - What is the London Smog?
Answer - Burning coal leads to emissions of Carbon dioxide, Sulphur dioxide and dust. When these pollutants mix with fog, droplets of highly corrosive Sulphuric Acid are produced in the air, and then London smog is formed. It occurs at very cold temperatures. In 1952, about 4,000 deaths were caused in Londor due to yellow fog. It lasted for 5 Days. This was called the Great London Smog.
Question - What is the Photochemical Smog?
Answer - This type of smog forms on sunny days and is the result of emissions from traffic. Nitrogenous oxides from car exhausts and hydrocarbons react in the presence of sunlight to produce a noxious mixture of aerosols and gasses.
Question - What are the effects of Photochemical Smog?
Answer - Today, smog is usually produced photochemically. This smog is produced when sunlight acts upon motor vehicle exhaust gases such as nitrogen oxides (NOx) and volatile organic compounds (VOCs).
1. Ozone is one of the main components of photochemical smog. It is a powerful oxidising gas. It attacks our tissues. It causes sore throats, inflammation, discharges in nasal passages etc.
2. Ozone affects lung function and the lower respiratory tract.
3. Ozone also attacks plants mainly citrus fruits, potatoes, legumes, soya beans etc.
4. Other photochemical smog components and ozone cause damage to buildings and degrades rubber, clothing etc.