Photochemical Smog

This Article Explains:

• What is photochemical smog?
• What are the common components of photochemical smog?
• What are the major sources of photochemical smog?
• How to Form photochemical smog?
• How its effect on environmental and human health?
• How to Control photochemical smog?
• Conclusion

UPSC Mains Based Question on Photochemical Smog: What is Photochemical Smog? Highlight the initiatives taken at various levels to curb the menace of photochemical smog. What is the composition of photochemical smog & how can photochemical smog be controlled?

 

What is photochemical smog?

Photochemical smog occurs in warm, dry and sunny climate. When the sun's ultraviolet rays interact with the atmosphere's nitrogen oxides and volatile organic compounds, photochemical smog is created. It appears as a brown haze and is most noticeable in the morning and late afternoon, particularly in warm, densely populated places. It has high concentration of oxidising agents and is, therefore, called as oxidising smog.

• When primary pollutants such organic chemicals and nitrogen oxides react with one another in the presence of Sunlight, a photochemical (summer smog) is created. Ozone (Secondary Pollutant), a gas, is created.

What are the common components of photochemical smog?

1. Ozone,
2. Nitric oxide,
3. Acrolein,
4. Formaldehyde and
5. Peroxyacetyl nitrate (PAN).

What are the major sources of photochemical smog?

The nitrogen oxides and volatile organic compounds (VOCs) are produced Naturally and Anthropogenic activities.

Natural Sources:

• Nitrogen oxides are produced in nature by bushfires, lightning, and soil microbiological activities.
• Terpenes, the hydrocarbons that give oils their ability to burn, are examples of naturally occurring molecules that can evaporate and release volatile organic compounds (VOCs).
• It has also been found that eucalyptus trees release considerable levels of these compounds.

Anthropogenic Sources:

• Volatile organic compounds (VOCs) are created when fossil fuels burn incompetently.
• Punjab and Haryana regions where there is stubble burning All the dust and contaminants that have become trapped in the air are carried by the wind.
• Air pollution from garbage dumps and industrial pollution is also rising, adding to the smog in the atmosphere.

How to Form photochemical smog?

• When fossil fuels are burnt, a variety of pollutants are emitted into the earth’s troposphere.
• When the reaction occurs between NO₂ and sunlight, which breaks up into nitric oxide and free oxygen atom.
• Oxygen atoms are very reactive and combine with the O₂ in air to produce ozone (O₃).
• Both NO2 and O3 are strong oxidising agents and can react with the unburnt hydrocarbons in the polluted air to produce chemicals such as formaldehyde, acrolein and peroxyacetyl nitrate (PAN).

Below image presents the formation of photochemical smog:

 

How its effect on environmental and human health?

• Photochemical smog causes serious health problems.
• It affected visibility, which leads to accidents.
• Both ozone and PAN act as powerful eye irritants.
• Ozone and nitric oxide irritate the nose and throat and their high concentration causes headache, chest pain, dryness of the throat, cough and difficulty in breathing.
• VOCs some compounds are carcinogens.
• Photochemical smog leads to cracking of rubber and extensive damage to plant life.
• It also causes corrosion of metals, stones, building materials, rubber and painted surfaces.
• Due to acid rain, which is corrode architectural monuments like Taj Mahal.

What is Smog? The word smog is derived from smoke and fog. This is the most common example of air pollution that occurs in many cities throughout the world. There are two types of smog: Classical smog occurs in cool humid climate. It is a mixture of smoke, fog and sulphur dioxide. Chemically it is a reducing mixture and so it is also called as reducing smog. Photochemical smog occurs in warm, dry and sunny climate. The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. Photochemical smog has high concentration of oxidising agents and is, therefore, called as oxidising smog.

 

How to Control photochemical smog?

• The concentrations of hydrocarbons, NOx, and other VOC emissions can be reduced to mitigate photochemical smog.
• Utilizing catalytic converters can reduce nitrous oxide, carbon dioxide, and hydrocarbon emissions from vehicles.
• Instead of using a car, try riding a bike or walking, and use public transport.
• If renovating or building, use energy-efficient designs and materials.
• Turn off unnecessary electrical appliances at the power point.
• Power generated from clean, renewable energy sources.
• Avoid products that release high levels of VOCs. For example, use low-VOC paints.

Government Initiatives:

• In order to raise awareness among the general public and implementing agencies in particular, the MoEFCC launched the National Clean Air Programme (NCAP) in April 2018. It was preceded by the Clean Air Programme in Delhi in February 2018.
• The gathering and distribution of air quality data take place from one centralized location. All stakeholders can access the air quality status in real time.
• Leap-frogging from BS-IV to BS-VI.
• The Supreme Court ordered the state governments of Punjab, Haryana, Uttar Pradesh, and Delhi to give small and marginal farmers financial support of Rs 100 per quintal for controlling paddy stubble.
• SAMEER app has been launched wherein air quality information is available to public along with provision for registering complaints against air polluting activities.
• Air quality information collection and dissemination are done from a centralized location. It provides real time air quality status to all stakeholders.

Photo chemical smog is commonly found in urban areas with high levels of vehicle emissions and industrial activities. Reducing emissions from these sources can help reduce the formation of photo chemical smog.

 

Reference: NCERT, PIB.