Particle size classification in air pollution: Particles with diameters in the range of about 5 to 200 micrometres are generally referred to as what?

Introduction / Context:
Airborne particulate matter is labeled according to formation mechanism and size because capture technologies and health effects differ by size class. Coarse mechanically generated particles are distinct from very fine combustion aerosols. This question focuses on the conventional name for particles in the 5–200 micrometre range.

Given Data / Assumptions:

• Size interval: approximately 5–200 µm.
• Particles are assumed solid and generated by mechanical processes such as grinding, crushing, or handling.
• Terminology follows common industrial hygiene and air pollution control usage.

Concept / Approach:
“Dust” typically refers to mechanically generated solid particles, often between about 1 and 100 µm, extending into the low hundreds of micrometres for coarser fractions. “Powder” is a general materials term, sometimes used for bulk solids rather than airborne particles. “Smoke” commonly denotes submicron to a few micrometres, formed by condensation of combustion products. “Colloids/aerosols” emphasize very fine particle suspensions, generally below 1–5 µm.

Step-by-Step Solution:
Match size and formation mechanism: 5–200 µm, mechanical generation → dust.Exclude alternatives: smoke and colloidal aerosols are much finer; powder is not an air pollution class.Select “dust.”

Verification / Alternative check:
Sampling device cut-points (e.g., PM10) show that dust can occupy the coarse fraction, consistent with the given size range, although the upper bound approaches settleable material.

Why Other Options Are Wrong:
Colloids/aerosols: Typically very fine suspensions, not 200 µm scale.Powder: Bulk material term; not specific to airborne fraction.Smoke: Very fine combustion-derived particles, mostly < 1 µm to a few µm.

Common Pitfalls:

• Using “powder” and “dust” interchangeably; only dust refers to airborne particles in this size class.
• Overlooking that coarse dust settles rapidly and is best controlled by enclosures and cyclones.

Final Answer:
dust