Smog word is derived from fog and smoke. The most common form of air pollution is Smog which has its appearance in so many cities across the globe. As you know that smog is usually in dense or urban areas and huge population regions. With any kind of atmospheric pollution, disregarding its composition, source, or concentration – which creates a noticeable reduction in the quality of atmospheric visibility.

Smog surrounds a wide air pollutants category that is created by a large group of processes which is particularly related to the atmospheric conditions of forming region.


So, mainly there are two basic smog types:

1. Classical smog: This type of smog takes place in a cold humid climate. Classical smog is a combination of fog, smoke, and sulphur dioxide. By chemical nature, it’s a reduction mixture and therefore, it’s even called the “reducing smog”.

2. Photochemical smog: This smog type has its appearance in dry, warm, and sunny weather. The prime components of which photochemical smog consist of are produced by sunlight’s reaction on nitrogen oxides and hydrocarbons which are produced by factories and automobiles. The Photochemical smog contains a high concentration of oxidizing agents or oxidants and therefore, it’s known as the “oxidizing smog”.

Photochemical Smog

Photochemical smog, which is generally seen in the Basin of Los Angeles. It’s primarily composed of nitrogen dioxide and ozone. At the time of ozone formation, nitrogen dioxide (NO2) exhausted from vehicle is photolyzed by the arriving solar radiation and which results in producing nitrogen oxide, plus an unpaired O (Oxygen atom).

After this, the solo or lone “O” atom combines with “O” molecule so as to produce ozone. In the case of normal conditions, most of the ozone molecules have the oxidation reaction to form nitrogen oxide and then again back to nitrogen dioxide form. It thus creates a practical cycle which results in a much slighter ozone formation adjacent to ground level.

Nevertheless, when VOCs (Volatile Organic Compounds) have their presence in the atmosphere, then the equation is completely changed.

VOCs which are highly reactive oxidizes nitrogen oxide in the form of nitrogen dioxide as it does not break down into any molecules of ozone during this process.

Composition of Photochemical Smog

Following are the substances which are analyzed during photochemical smog:

1. (NO2) Nitrogen Dioxide from the exhaustion of vehicle and that is photolyzed by the (UV) ultraviolet radiation () directly from the Sun and then decomposes in the form of (NO) Nitrogen Oxide along with the oxygen radical:


2. Then, the oxygen radical reacts with the molecule of atmospheric oxygen to have the formation of ozone, O3:


3. During normal conditions, Ozone (O3) has a reaction with NO, which results in producing NO2 and thus, the oxygen molecule:



Some other substances which are found are:

  • VOC’s reaction with the hydroxide to create a reactive molecule of VOC and water


  • R.+O2→RO2
  • RO2+NO→RO−.+NO2

Here, RO2 is oxidized VOC* and R. is reactive VOC molecule

How To Control Photochemical Smog

You’ll be surprised to know that every fresh article which is sold in the US should be including a “catalytic converter” to lessen photochemical emission. The catalyst converters pressurize CO and not so completed combustible hydrocarbons having the reaction with the metal catalyst, usually platinum to produce H2O and CO2.

In addition, catalytic converters have the ability to reduce the nitrogen oxides from exhaustive gases into N2 and O2, with that, there’s elimination of ozone cycle formation. A lot of scientists suggested that at night, pumping of gas can lessen the “photochemical ozone formation” by restricting the amount of risk VOCs is having with sunlight.


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