What is Photochemical Smog & Its Reactions?

Earth has been facing a number of hazardous issues regarding air pollution like smog. Now it has become a routine matter that crowded cities have been polluted and they want a moment to breathe freely. Human beings require clean air to breathe freely. However, the growing problems of smoke, fog, and smog have made the earth a vulnerable place to live in. Let’s have a look at what is photochemical smog, its reactions, its formation, sources of indoor air pollution, photochemical smog effects and how to prevent smog.

London has experienced acute smog during the nineteenth and 20th century. As a result of a rise in air pollution, “The Great Smog of 1952” was identified which resulted in 4000 deaths. Photochemical smog was discovered in the 1950s and later on its drastic impacts, reactions and chemical compounds were revealed.

Thus, the air quality suffers as the combustion of fossil fuel has been a continuous practice and more common than the burning of coal. Air pollution is not only destroying our atmosphere, but the whole nature has been suffering at the hands of molecules of pollutants.

what is photochemical smog

What is Photochemical Smog?

Smog basically comes into formation when the fog gets mixed with smoke. On the other hand, when this kind of smog combines with certain types of pollutant molecules in the atmosphere reacts with the photons of sunlight, they become photochemical smog.

These photons undergo a chemical reaction with the pollutants and convert them into a mixture of dangerous chemicals. This formula results in a smog called photochemical smog. Thus, photochemical smog comprises of a variety of harmful chemicals.

These chemicals are nitrogen oxides, ozone, volatile organic compounds (VOCs), peroxyacytyl nitrate, aldehydes, and other secondary pollutants. When the ultraviolet rays of the sun react with nitrogen oxide present in the atmosphere, smog is produced.

Apparently, it is visible in the form of a brown haze layer covering the atmosphere. Usually, smog gets prominent at the morning time and afternoon. Therefore, it is quite obvious that during the morning time, nitrogen oxide is emitted from the car engines.

photochemical smog reactions

Photochemical Smog Reactions

Upon combustion of fossil fuel, nitric oxide NO and nitrogen dioxide NO2 are emitted. There are some other outdoor sources of air pollution like volcanos, forest fire, motor vehicles, and the emission of pollutants from industry, windblown dust, and fuel burning.

Thus, nitrogen oxide reacts with water in order to form nitric acid. It may also react to the sunlight in order to produce oxygen. Later on, this oxygen then reacts with the molecular oxygen to produce Ozone.

So, nitric acid may convert into acid rain or it remains in the form of smog. Moreover, due to the direct production of nitrogen oxide from the vehicles, most of the cities have been affected by pollution. Therefore, smog quantity is quite high in warm and densely populated cities like Los Angeles, United States, Mexico City, Sydney, Beijing, and many more locations.

Sources of Air pollution

As photochemical smog is a mixture of secondary and primary compounds. These are directly or indirectly released into the atmosphere through automobiles, industries and after certain chemical reactions.

photochemical smog effects have drastic impacts on the atmosphere and it makes difficulties of human beings as well. Inhaling pollutants may lead them to develop breathing issues. Apart from that increased level of smog in the air causes irritation in the eyes and lungs.

Researches show that most of the chemical pollutants present in air pollution are the result of emission through burning coal and combustion of fossil fuel. Thus, with the release of these dangerous pollutants, photochemical smog reactions have adverse effects on human health due to poor air quality.

On the other hand, there are natural causes of photochemical smog effects that may come up with smog creation. These are things emitted as a result of a volcano eruption or a forest fire. These are actually more dangerous because natural emission affects air quality at a greater range.

photochemical smog effects take place at the moment when the ultraviolet rays of the sun react with the nitrogen dioxide (NO2). As a result of this reaction, nitrogen dioxide undergoes a complex chemical reaction with hydrocarbons of the pollutants as well.

sources of indoor air pollution

Primary and Secondary Air Pollutants

In this way, photochemical smog reactions produce a mixture of components. This mixture of components comprises of ozone, nitric acid, aldehydes, peroxyacyl nitrates PANs. These are some of the secondary pollutants produced along with the primary ones.

Out of these complex and hazardous chemicals, nitrogen dioxide NO2, ozone, and peroxyacyl nitrates PANs pose a major threat to living beings. These pollutants produced as a result of photochemical smog reactions are called photochemical oxidants.

Moreover, these photochemical oxidants have a characteristic of reacting and oxidizing in the atmosphere. Therefore, once these are exposed to air they oxidize certain compounds into it. Alarmingly, these oxidants, which do not normally oxidize reacts in the lungs of a person.

Above all, these chemicals are injurious to human and animal health even in a small quantity. It may cause reduced visibility along with a number of ailments connected with respiration. Photochemical smog reactions affect the respiratory tracts due to the pollution in the air.

Not only humans, animals, but plants like crops and trees undergo the worst changes due to these pollutants. Thus, smog is a type of air pollution, which has drastic impacts on the human body and it damages the nature as a whole.

Sources of Indoor Air Pollution

Out of the aforementioned photochemical smog pollutants and molecules, nitrogen oxides come out of car and truck engines. On the other hand, volatile organic compounds (VOCs) are produced from paints, gasoline, and pesticides.

Here are mentioned some common indoor sources which have increased air pollution in our lives.

  • Tobacco smoke is one of the major sources of indoor air pollution. The chemical that is inhaled and exhaled through a pipe, cigar, and cigarette. Hence, environmental tobacco results in lung cancer, heart diseases along with irritation in the lungs, eyes, nose, and throat.
  • Then comes, carbon monoxide released from chimneys, gas stoves, heaters, wood stoves, and furnaces. This gas can prove fatal for you, and it may cause nausea, dizziness followed by headaches.
  • Pesticides are another major source of indoor air pollution. It is used in killing unwanted organisms and therefore you cannot inhale it. Due to a continuous release of certain chemicals from pesticides, inhaling them may cause irritation in the eyes, nose, and throat. Moreover, it may cause damage to your central nervous system and kidneys.
  • Asbestos is another material if it gets inhaled may cause abdominal cancer or lung cancer. This material has been used in the construction of houses and unknowingly released in the air to produce pollution.

how to prevent smog

How to prevent Smog?

Smog is injurious to human health and in the long run, it may prove fatal as well. However, if we change our lifestyle, we may help to minimize its danger levels. We all know that huge traffic on roads is the main cause of dense smog in big cities. According to research, 50% of smog has produced as a result of the emission of gases from vehicles, which is one of the main reasons for photochemical smog formation.

Every year brings more vehicles on the road and brings more smoke. Similarly, the burning of fossil fuel and coal in the industrial sector has immensely increased air pollution. This is quite alarming that everyone prefers to travel through their own vehicle rather than walking.

Moreover, deforestation and no proper mechanism for tree plantation have aggravated the situation. Hence, air pollution is growing at the same pace as that of the population. However, there are certain things that we can do to prevent photochemical smog formation to save the next generation from its drastic impacts.

Methods to prevent Emission of Dangerous Air pollutants

Let me tell you how to prevent photochemical smog formation simply by changing our lifestyle.

  • If we prefer to walk to our office or any other place instead of driving any vehicle, we can minimize smog together. You can use public transport for remote areas as well.
  • Through regular maintenance of your cars, you can improve gas mileage and reduce poisonous emissions to some extent.
  • You can reduce the production of volatile organic compounds (VOCs) by using paints with lower VOCs.
  • On the other hand, it is better to fuel up your desired vehicle or any other machinery at night or during cooler hours of the days. This is another major change you can bring towards minimizing the photochemical smog pollutant production. In other words, this change of timing and hours will eventually reduce the heating of gas fumes. And this will reduce the emission of ozone gas as well.
  • Furthermore, you can also use electric appliances instead of fuel or gas consuming appliances.
  • By using environmentally-friendly consumer goods can reduce the emission of pollutants and prevent smog.

Therefore, it is suggested that through changing our behavior and lifestyle, we can minimize photochemical smog formation and its adverse effects.


Hopefully, this article has created awareness regarding the damages caused by smog. Moreover, we can individually help to reduce the emission of smog-producing elements. Thus, this is the only way to prevent smog that we inhale every day and keep the air clean. But, this can only be possible through behavioral changes in our lifestyle and a shift towards the eco-friendly standard of life.

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