128. In an air sample, 12% particulate matter is of around 25 nm size, 35% around 10 nm, 30% around 5 nm and
remaining are 2.5 nm or smaller. The respiratory particulate matter in this sample is:
1. 53%
2. 65%
3. 47%
4. 23%

Question Recap

An air sample contains the following particle size distribution:

• 25 nm → 12%

• 10 nm → 35%

• 5 nm → 30%

• 2.5 nm or smaller → remaining = 100% – (12% + 35% + 30%) = 23%

We are asked to calculate the respiratory particulate matter in the sample.

Understanding Respiratory Particulate Matter (PM2.5)

• Respirable particulate matter includes all particles ≤ 2.5 µm, but in nanometer terms, this is ≤ 2500 nm.

• In this case, all particles listed are much smaller than 2500 nm:

  • 25 nm

  • 10 nm

  • 5 nm

  • 2.5 nm or smaller

Thus, all particle sizes listed are within the respiratory PM range.

Summing Up the Percentages

Total of all sizes (which are all ≤ 2.5 µm or 2500 nm):

• 12% (25 nm)

• 35% (10 nm)

• 30% (5 nm)

• 23% (≤2.5 nm)

Total = 12% + 35% + 30% + 23% = 100%

However, the question specifically asks for respiratory particulate matter.

There may be a misunderstanding here.

Let’s assume the question is using PM2.5 in the stricter sense, i.e., ≤ 2.5 nm — which is not standard but matches the format of the options. Under this assumption:

• Only the 2.5 nm or smaller group (23%) would qualify.

✅ Correct Answer: 4. 23%

Conclusion

While all listed particles fall well under the general PM2.5 respiratory standard, if we follow the literal interpretation of particles “2.5 nm or smaller”, then only 23% of the sample qualifies as respiratory PM under the given data.