SO₂ odor threshold in ambient air At approximately what concentration of sulphur dioxide (SO₂) in air does a distinctly pungent smell become noticeable?

Introduction / Context:
Sulphur dioxide (SO₂) is a key air pollutant from combustion of sulfur-bearing fuels. Recognizing odor thresholds helps in field diagnosis of emissions and potential health impacts.

Given Data / Assumptions:

• The question asks for the approximate concentration at which SO₂ odor is distinctly pungent.
• Units are parts per million (ppm) in air.
• We seek an order-of-magnitude threshold used in conventional environmental MCQs.

Concept / Approach:
Human odor detection thresholds for SO₂ are often cited near sub-ppm to around 1 ppm, with a distinctly irritating/pungent sensation in the vicinity of 1 ppm and above. Lower values (0.01–0.1 ppm) may be detectable to very sensitive individuals but are not the commonly cited “pungent” threshold in basic references.

Step-by-Step Solution:

Verification / Alternative check:
Occupational hygiene sources describe eye and respiratory irritation escalating from low single-digit ppm upward; therefore, 1 ppm as a pungent threshold aligns with didactic values.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing minimal detection by highly sensitive individuals with a broadly accepted educational threshold for pungency.

Final Answer:
1