Particle diameter in microns (µm)

            Particles

• Particle size expressed in microns or micrometers
  (1 µm=1/1,000,000 m = 0.00003937 inches)
• Diameters of various particles
• EPA definitions and terminology
• Interaction of particles with the human body
• Interaction of particles with light
• Microscopic images: Sizes and shapes of various
  air-borne particles.

Photo from EPA website, http://www.epa.gov/pm/basic.html.

Particle diameter in microns (µm)

Particle diameter in microns (µm)

 Why 10 μm particle size is important

• Particles < 10 μm are inhalable (can enter the lungs),
  and are potentially problematic for human health.
• Particles > 10 μm do not get inhaled into the lungs, but
  get trapped in the nose or throat.
• EPA is concerned with particles less than 10 μm (“coarse
  particles”), because of their potential effect on the lungs.
• EPA labels these coarse particles as PM10 (“Particulate
  Matter less than 10 microns”), and lists them among
  the 7 CAPs (Criteria Air Pollutants) for which the EPA
  issues NAAQS (National Ambient Air Quality Standards) for healthy air.

Particle diameter in microns (µm)

 Why 2.5 μm particle size is important

• Particles < 2.5 μm are respirable – can penetrate deep into the lungs, and are potentially more problematic for human health than PM10.
• EPA is most concerned with these small particles (“fine particles”), because of their effect on the lungs.
• EPA labels these small particles as PM2.5 (“Particulate Matter less than 2.5 microns” or “fines”), and lists them among the 7 CAPs (Criteria Air Pollutants) for which the EPA issues NAAQS (National Ambient Air Quality Standards) for healthy air.

How Small of a Particle Can We See?

• Estimates vary, but range from Dp = 20 to 100 μm as the smallest object a healthy naked human eye can see.
• On average, most people can distinguish objects down to about 70 μm, about the size of a single strand of hair.
• However, it the object is a glowing particle or a particle that scatters light and is seen by the eye as a source of light (e.g. bubbles, transparent particles that scatter sunlight, etc.), a healthy human eye can see down to about Dp = 10 μm.
• Many air pollution particles scatter light, so 10 μm is a useful benchmark: The naked eye can see individual air pollution particles down to about 10 μm.
• However, we can see clouds of smaller (even submicron!) particles because of blockage and scattering of light.

                                                                                                 The tracheobronchial region

• Also called the conducting airway
• The trachea divides into two primary bronchi (one to each lung)
• Each primary bronchus divides again and again at least 20 times – the bronchial tree
• Bronchi move air in and out of the lung, but do not exchange gases with the blood
• Bronchi are lined with mucus and hair-like organs called cilia that expel particles up and out of the trachea

                                                                                                   The pulmonary region

• Also called the respiratory airspace
• At the end of each bronchiole are clusters of air sacs called alveoli
• Alveoli contain thin membranes in which air and other gases are exchanged with the blood
• Total useful surface area of alveoli is over 100 m2 – about half the surface of a tennis court (261 m2)!
• Alveoli do not have cilia, but instead remove particles through white blood cells called macrophage

Particle sizes and shapes

From: The PARTICLE ATLAS

EDITION TWO

 An encyclopedia of techniques for small particle identification

Volume IV

The Particle Analyst’s Handbook

Walter C. McCrone

John Gustav Delly

Copyright 1973, Ann Arbor Science Publishers, Inc., Ann Arbor MI.

 Human hair

(The hairs shown here range between 50 and 150 µm

in diameter, and are smooth and straight)

 Human hair fragments after shaving

(also some skin cells and dirt)

Asbestos

(lots of hairy fibrils, which are < 1 µm diameter)

Fiber glass

(straight smooth cylinders, 8 µm diameter)

Fiber glass dust

(irregular shapes, 10 to 25 µm long)

This is what you breathe when working in your attic!

Ragweed pollen

(about 18 to 20 µm diameter, spherical)

Mold

(spherical heads ≈ 40 µm diameter,

tails about ≈ 10 µm diameter, and spores ≈ 4 µm)

Deodorant spray powder (talc)

(various diameters > 1 µm)

Combustion products from underfeed coal stoker

(1 to 150 µm dia., irregular shapes, lots of unburned

fuel, impurities, and ash)

Ammonium sulfate (sometimes from power plants)

(very uneven irregular shapes, 10 to 100 µm or larger)

Electric arc furnace dust

(individual particles < 2 µm diameter, but coagulate

into much larger irregular shapes)