Appendix C 411
Mechanical abrasion and air motion may cause particle release from
indoor materials. Particles are also produced by people, e.g., skin flakes
are shed and droplet nuclei are generated from sneezing and coughing.
Some particles may contain toxic chemicals. Some particles, biologic in
origin, may cause allergic or inflammatory reactions or be a source of
infectious disease. Increased morbidity and mortality is associated with
increases in outdoor particle concentrations (EPA 1996), even when con-
centrations are in the vicinity of the U.S. national ambient air quality
standard (50 μgÆm^3 for particles smaller than 10 micrometer). Of par-
ticular concern are the particles smaller than 2.5 micrometers in diam-
eter, which are more likely to deposit deep inside the lungs (EPA 1996).
A national ambient air quality standard for particles (http://www.epa.
gov/airs/criteria. html) smaller than 2.5 micrometers was established
by the US Environmental Protection Agency (EPA) in 1997 (15 μgÆm^3
for the three-year average of the annual arithmetic mean concentration;
65 μgÆm^3 24-hour average).
Particle size is important because it influences the location where
particles deposit in the respiratory system (EPA 1996), the efficiency of
particle removal by air filters, and the rate of particle removal from in-
door air by deposition on surfaces. The large majority of indoor particles
are smaller than 1 μm. Particles smaller than approximately 2.5 μm are
more likely to deposit deep inside the lungs. Many of the bioaerosols
are approximately 1 μ and larger, with pollens often larger than 10 m
μm. These larger particles deposit preferentially in the nose.
Non-infectious bioaerosols include pollens, molds, bacteria, dust
mite allergens, insect fragments, and animal dander. The sources are
outdoor air, indoor mold and bacteria growth, insects, and pets. These
bioaerosols may be brought into buildings as air enters or may enter
buildings attached to shoes and clothing and subsequently be resus-
pended in the indoor air. The health effects of non-infectious bioaero-
sols include allergy symptoms, asthma symptoms, and hypersensitivity
pneumonitis which is characterized by inflamation of the airway and
lung (Gammage and Berven 1997).
Infectious non-communicable bioaerosols are airborne bacteria
or fungi that can infect humans but that have a non-human source
(Gammage and Berven 1997). The best known example is Legionella,
a bacterium that causes Legionnaires Disease and Pontiac Fever. Cool-
ing towers and other sources of standing water (e.g., humidifiers) are
thought to be a source of aerosolized Legionella in buildings. Legio-