Question

Which one of the following is a primary air pollutant?

• A. Ash from a volcanic eruption
• B. Tropospheric Ozone
• C. Stratospheric Ozone
• D. PAN

Hint:

To distinguish between primary and secondary pollutants, ask "Does it come directly out of a source?" If yes, it's primary (like CO, SO\(_2\), ash). If it's formed by chemical reactions in the air, it's secondary (like O\(_3\), PAN, acid rain).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The question asks to identify a primary air pollutant from the given options. Primary pollutants are substances directly emitted into the atmosphere from a source (e.g., from a factory chimney or a volcanic eruption). Secondary pollutants are not directly emitted but form in the atmosphere when primary pollutants react with each other or with other atmospheric components.

Step 3: Detailed Explanation:
\[\begin{array}{rl} \bullet & \text{(A) Ash from a volcanic eruption: This is a primary pollutant. Volcanic ash is a particulate matter that is directly emitted from a natural source (the volcano) into the atmosphere.} \\ \bullet & \text{(B) Tropospheric Ozone (O\(_3\)): This is a classic example of a secondary pollutant. It is formed in the troposphere by the reaction of primary pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight.} \\ \bullet & \text{(C) Stratospheric Ozone: This is not a pollutant. The ozone layer in the stratosphere is essential for life on Earth as it absorbs harmful ultraviolet (UV) radiation.} \\ \bullet & \text{(D) PAN (Peroxyacetyl nitrate): This is another common secondary pollutant, formed from the reaction of NOx and VOCs, and is a component of photochemical smog.} \\ \end{array}\]

Step 4: Final Answer:
Ash from a volcanic eruption is a primary air pollutant.