Question

Which of the following is a natural source of aerosols?

• A. Volcanic eruptions
• B. Industrial emissions
• C. Deforestation
• D. Automobile exhaust

Hint:

• Aerosols are fine solid or liquid particles suspended in the air.
• Natural sources: Volcanic eruptions, dust storms, sea spray, wildfires, biogenic emissions (pollen, VOCs from plants).
• Anthropogenic sources: Industrial emissions, vehicle exhaust, burning fossil fuels and biomass.
• Volcanic eruptions are a major natural event that injects large quantities of aerosols into the atmosphere.

Answer 1

The Correct Option is A

Aerosols are tiny solid or liquid particles suspended in a gas (usually air). They can originate from both natural and anthropogenic (human-caused) sources. Natural sources of aerosols include:

• Volcanic eruptions (option a): Volcanoes release large amounts of ash, dust, and gases (like sulfur dioxide, which can form sulfate aerosols) into the atmosphere.
• Dust storms: Wind erosion of dry soils can lift dust and mineral particles into the air, especially in arid and semi-arid regions.
• Sea spray: Breaking waves inject sea salt particles into the atmosphere.
• Wildfires: Smoke from naturally occurring wildfires releases soot (black carbon), organic carbon particles, and other aerosols.
• Biogenic sources: Plants release volatile organic compounds (VOCs) that can react in the atmosphere to form secondary organic aerosols. Pollen and fungal spores are also biogenic aerosols.

Anthropogenic sources of aerosols include:

• Industrial emissions (option b): Factories and power plants release various particles and precursor gases (like SO$_2$, NO$_x$) that form aerosols.
• Automobile exhaust (option d): Vehicles emit soot, organic compounds, and precursor gases for secondary aerosol formation.
• Burning of biomass: Agricultural burning and burning of wood for fuel.
• Deforestation (option c): While deforestation itself is an activity, it can lead to increased soil erosion and dust (aerosols), and the burning associated with deforestation releases smoke aerosols. However, volcanic eruptions are a more direct and classic example of a natural aerosol source.

Among the given options, volcanic eruptions are a direct and significant natural source of aerosols. Industrial emissions and automobile exhaust are anthropogenic. Deforestation is an activity that can indirectly lead to aerosol generation. \[ \boxed{\text{Volcanic eruptions}} \]