Which of the following is not the common component of photochemical smog?
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Remember the two main types of smog and their key components:
1. \textbf{Photochemical Smog (oxidizing):} Primary pollutants are NOx and VOCs. Secondary pollutants are Ozone (\(O_3\)), PAN, aldehydes (Formaldehyde, Acrolein). Needs sunlight.
2. \textbf{Classical Smog (reducing):} Primary pollutant is Sulphur Dioxide (\(SO_2\)). Needs cool, humid conditions.
Photochemical smog, also known as Los Angeles-type smog, is a type of air pollution that forms when sunlight acts on certain pollutants.
The primary pollutants that lead to photochemical smog are nitrogen oxides (NOx) and volatile organic compounds (VOCs), which are emitted from vehicle exhausts and industrial processes.
The key chemical reactions involve sunlight (photo-) splitting nitrogen dioxide (NO\(_2\)) to form nitric oxide (NO) and a highly reactive atomic oxygen (O).
1. \( \text{NO}_2 \xrightarrow{sunlight} \text{NO} + \text{O} \)
This atomic oxygen then reacts with molecular oxygen (\(O_2\)) to form Ozone (\(O_3\)), which is a major component of photochemical smog.
2. \( \text{O} + \text{O}_2 \rightarrow \text{O}_3 \)
The reactive atomic oxygen and ozone also react with the VOCs in the atmosphere to produce a variety of harmful secondary pollutants. These include:
- Formaldehyde (HCHO)
- Acrolein (CH\(_2\)=CHCHO)
- Peroxyacetyl nitrate (PAN)
These secondary pollutants cause eye irritation and respiratory problems. Sulphur dioxide (\(SO_2\)), on the other hand, is the primary pollutant responsible for classical smog, also known as London-type or sulfurous smog. This type of smog forms in cool, humid conditions and is characterized by high concentrations of SO\(_2\), sulfuric acid aerosols, and particulate matter from the burning of sulfur-rich fossil fuels like coal.
Therefore, sulphur dioxide is not a common component of photochemical smog.
