How does sunlight contribute to the formation of smog?

Sunlight contributes to the formation of smog by triggering chemical reactions between pollutants in the atmosphere.

Smog, a type of air pollution, is a mixture of smoke and fog. It is primarily composed of ground-level ozone, a harmful air pollutant. The formation of smog is a complex process that involves various chemical reactions between pollutants in the atmosphere. Sunlight plays a crucial role in these reactions.

The primary pollutants involved in the formation of smog are nitrogen oxides (NOx) and volatile organic compounds (VOCs). These pollutants are emitted by various sources such as vehicles, industrial processes, and power plants. Once these pollutants are released into the atmosphere, they react with each other under the influence of sunlight to form ground-level ozone, the main component of smog.

The chemical reaction that leads to the formation of ground-level ozone is a photochemical process, meaning it is driven by light. Nitrogen oxides and volatile organic compounds react in the presence of sunlight to produce ozone. This reaction is accelerated by higher temperatures, which is why smog is more common in summer months.

The reaction can be summarised as follows: Nitrogen dioxide (NO2), a type of nitrogen oxide, absorbs sunlight and breaks down into nitric oxide (NO) and a free oxygen atom (O). This free oxygen atom can then react with oxygen molecules (O2) in the air to form ozone (O3).

In addition to ozone, these reactions also produce other harmful pollutants, such as peroxyacetyl nitrate (PAN) and aldehydes. These secondary pollutants further contribute to the harmful effects of smog.

In conclusion, sunlight is a key factor in the formation of smog. It triggers the chemical reactions between nitrogen oxides and volatile organic compounds, leading to the production of ground-level ozone and other harmful pollutants. Therefore, efforts to reduce smog must focus not only on reducing emissions of primary pollutants but also on understanding and managing the role of sunlight in smog formation.