E-2
PART I GENERAL DESCRIPTION ON AIR CLEANING
If you could see the air you breathe under a microscope, you might be in for a surprise. The air quality is much more terrible
than you may think. In fact, floating in indoor air is a "soup" of particles too small to be seen by your naked eye. But it is large
enough to cause problems. Visible dust makes up only 1% of all the particles in the air. The vast majority of particles are
microscopic.
How long the particles float in the air depends on their size. Relatively
"heavy"
dust particles (more than 5 microns) tend to
settle out of the air in 20 minutes or less. They form the dust that's easily wiped away on tables and other surfaces.
Middleweight
particles (from 1 to 5 microns) may remain airborne for hours before falling out of the air.
Lightweight
particles
(less than 1 micron) can remain suspended permanently in the air. And particles sized less than 1 micron can gain the easiest
entry to your body and place the biggest burden on its defense system.
No matter the type or size of the building - single family home, office, school, store, hotel, restaurant, hospital, or other places
creating and maintaining good indoor air quality (IAQ) requires three key strategies:
source control
,
ventilation
and
air
cleaning
. Indoor air is an intriguing, complex environment that contains a myriad of visible and invisible contaminants. These
contaminants generally fall in one of two categories: particulates or gases, vapors and odors.
Particulates
Particulates are particles that are small enough to suspend in the air. Suspended inorganic particles, such as dust, pollen, fibers
or smoke to name a few examples, are often referred to as aerosols. Suspended organic compounds and small living
organisms, such as bacteria and viruses; mold spores and pieces of a mold colony; dust mites feces and body fragments;
cockroach body parts; and dander from cats, dogs and other mammals, are called bio-aerosols.
Particle size is measured in terms of its aerodynamic properties and is expressed as microns in diameter. Particles can range in
size from very small, which can remain in the air for a long time, up to relatively large, which quickly settle out of calm air. Table
1 lists common indoor contaminants and their particle sizes.
Inhaling particulates can cause eye, nose and throat irritation and increase the risk for respiratory infections. Health care
professionals are especially concerned about the long-term effects of inhaling fine particles (less than 2.5 microns), because
they can travel deep into the lungs where they can remain embedded for years or be absorbed into the bloodstream. Asbestos
and various substances in environmental tobacco smoke (ETS) are well-known examples and some are recognized
carcinogens. Exposure to high levels of fine particles also can play a role in developing respiratory diseases such as asthma,
bronchitis, pneumonia and emphysema. Larger particles (greater than 10 microns) do not cause as much concern, because
they get caught in the nose and throat and are cleared from the respiratory tract by coughing or swallowing.
Gases, Vapors and Odors
The types of gases or vapors most often found in indoor environments include combustion byproducts, such as carbon
monoxide, nitrogen oxides, sulfur dioxide, soot particles and polycyclic aromatic hydrocarbons (PAHs); pet, human and cooking
odors; ETS; volatile organic compounds (VOCs); microbial VOCs; and mycotoxins. Many of these substances also produce
odors, some of which are pleasant while others can be distracting and irritating. Moisture also is a vapor that must be monitored
as too much moisture can support indoor mold growth.
Volatile organic compounds are prevalent in all indoor environments, with as many as 100 to 1,000 different VOCs in the air
where people can easily inhale them. Exposure to VOCs in offices and other business establishments can cause building
occupants to feel uncomfortable, distracted or sick to the point that it interferes with their ability to do their work or reduces their
motivation to work. Reducing the level of VOCs also is very important in homes and schools, because children breathe in more
air with respect to their body mass than adults and thus have greater exposure to indoor air pollutants. Some types of mold also
emit VOCs, known as microbial VOCs or MVOCs, which are responsible for the characteristic musty, earthy odors associated
with mold. People who are sensitive to MVOCs may experience eye, nose and throat irritation.
Table 1. Particle Sizes of Common Indoor Contaminants
Particle
Skin flakes
Visible dust, lint
Dust mite
Mite allergen
Mold, pollen spores
Cat dander
Bacteria
Viruses
Amoeba
Particle
Asbetos
Re-suspended dust
Environmental tobacco smoke
Diesel soot
Outdoor fine particles (sulfates, metals)
Fresh combustion particles
Metal fumes
Ozone
Mineral fibers
Size
(micron)
1-40
>25
50
5-10
2-200
1-3
0.05-0.7
<0.01-0.05
8-20
Size
(micron)
0.25-1
5-25
0.1-0.8
0.01-1
0.1-2.5
<0.1
<0.1
<0.1
3-10
1. IN DOOR AIR QUALITY
ENGLISH
