Natural gas fired fireplaces introduce relatively small amount of soot and other particles into the home but they do contribute some. Heat modified glass fibers, the mock ember bed, may also be introduce into the living space.

The dark shading that forms behind picture frames on walls, at the baseboard, on walls at the ceiling, above incandescent lights near the ceiling, and other locations are due to the diffusional deposition of very small particles, typically dominated by combustion particles such as soot.

Humans generate as much as 5 million skin flakes per minute in the home.

Humus is a broad category that includes degraded biological materials that come in on shoes, on pets, or from animals in the environment.

There are over 120 different types of mites that live in homes. Most of them can cause health effects in sensitive people. Typical allergen testing is sensitive to only two types of mite and these two are often not the most common in a home. Mite allergens are in the frass (feces) as well as the body parts of the mite.

Starch is a very common particle in all environments but can be very high in homes. Starch is used in cosmetics, body powders, as a powder on elastomers and plastics to prevent sticking, in some carpet fresheners, food, etc. Bathrooms, bedrooms, and the kitchen tend to be the rooms with the most starch. The last set of three photographs show the same field of view with different analytical lighting.

Cigarette ash has a very high crystalline ash content due to the potassium nitrate and other additives to the tobacco. Cigar ash and other plant ashes have much less optically active ash. There is generally some charred plant residue that can be used to identify leaf or other plant parts.

These particle are an indication of the intrusion of exterior air or track-in debris into the interior space.

These particles are the result of exposure to smoke from fires inside or out side the home.