Photochemical Smog

Photochemical smog, also known as summer smog, is a type of smog that is produced when UV light originating from the sun interacts with the oxides of nitrogen present in the atmosphere. This type of smog usually manifests as a brown haze and is most commonly seen in highly populated cities that are placed in relatively warm climates. Furthermore, photochemical smog is most prominently visible during the mornings and afternoons.

How is Photochemical Smog Formed?

Photochemical form is formed by a complex series of chemical reactions involving sunlight, oxides of nitrogen, and volatile organic compounds that are present in the atmosphere as a result of air pollution. These reactions often result in the formation of ground level ozone and certain airborne particles. The formation of photochemical smog is closely related to the concentration of primary pollutants in the atmosphere. It is also related to the concentration of secondary pollutants (in some cases).

Common examples of primary pollutants that contribute towards photochemical smog include oxides of nitrogen such as nitric oxide, nitrogen dioxide, and nitrous oxide and most VOCs (volatile organic compounds). Common examples of secondary pollutants that contribute towards the formation of photochemical smog include aldehydes, tropospheric ozone, and peroxylacyl nitrates (often abbreviated to PAN).

During peak-traffic hours in the morning, large amounts of nitrogen oxides and volatile hydrocarbons are released into the atmosphere. These pollutants can be traced to automobile emissions and industrial discharge. Some of these hydrocarbon pollutants rapidly undergo oxidation by the hydroxyl groups in the atmosphere, resulting in the formation of peroxy radicals. These peroxy radicals go on to convert nitric oxide into nitrogen dioxide.

What are the Effects of Photochemical Smog?

Photochemical smog has a number of negative effects on the environment and human beings. The chemicals contained within it, when combined with hydrocarbons, form molecules which cause eye irritation. The atmospheric radicals interfere with the nitrogen cycle by stopping ground level ozone from being eliminated. Ground level ozone can prove to be extremely toxic to human beings. Other negative symptoms associated with photochemical smog include decreased vision and shortness of breath.

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Frequently Asked Questions on Photochemical Smog

What is the composition of photochemical smog?

Nitric oxide (a nitrogen compound with the formula NO) and nitrogen dioxide (another nitrogen compound with the chemical formula NO2) are often produced as a result of the burning of fossil fuels. These pollutants are also naturally released due to events such as the eruption of volcanoes and the occurrence of forest fires. However, the vast concentration of these pollutants in areas that are densely occupied by humans is of great concern. This is because natural emissions tend to continue to spread over much wider areas.

When it is exposed to ultraviolet radiation, the NO2 molecule is known to undergo a complex series of hydrocarbon reactions to produce the photochemical smog components. These components include a mixture of ozone, aldehydes, nitric acid, peroxyacyl nitrates (abbreviation: PANs) and many other secondary pollutants.

What are the effects of photochemical smog?

Photochemical smog is created by the interaction of sunlight with certain atmospheric chemicals. Ozone is the principal component of air pollution of this kind. Ozone in the stratosphere protects us from harmful ultraviolet radiation but it is detrimental to human health when it is present on the ground level.

How can photochemical smog be controlled?

The most obvious way to minimize photochemical smog levels is to eliminate the use of fossil fuels by using non-polluting or sustainable sources of electricity, such as nuclear power, hydropower, and wind power.

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