1. Indoor Air Quality
Sadhana S. Rayalu and Vaishali Khaparde
Air Pollution Control Division, NEERI, Nagpur - 440020
Introduction :
Indoor air pollutants are unwanted sometimes harmful materials in the air.
They range from dusts to chemicals to radon and are emitted from an incredible
variety of sources from the printer or photocopier, from building materials,
cigarette smoke etc. The result is often termed as "Sick building syndrome".
Typical symptoms may include headaches, unusual fatigue, itching or burning of
eyes, skin irritation, nasal congestion, dry or irritated throats, asthma attacks,
breathing problems, dizziness, memory loss, depression, sinus infections, colds,
flue and viruses. The EPA states that health effects from indoor air pollutants
may be experienced soon after exposure or possibly years later. EPA report also
says that "Indoor air is on average 2 to 10 times as polluted as worst outdoor air".
Indoor air quality is influenced due to emission of new materials and
products from building materials, insulation, bonding resins, fabrics, cleaning
materials, personal care products, pesticides, and in addition, from the
combustion process of cooking, fuel heating and tobacco smoking. Contaminants
originating outdoors infiltrate into the buildings and also affect the indoor air
quality. Human beings are exposed to elevated levels of a wide spectrum of
chemicals, many of which have been found to be even carcinogenic. Air quality
problems depend largely on climate and the economic requirements. In colder
and temperate zones of developed country, buildings, normally, have central
heating systems. To conserve energy both for economic and environmental
reasons, energy-efficient building construction has resulted in significant
reductions of the outdoor-indoor air exchange rate with an increase in indoor
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2. contaminant levels. Further, outdoor pollution is minimized to a greater extent
due to dispersion and dilution. From a health perspective, indoor health quality is
more important as people spend more that 80% of their time indoors such as
homes, schools, office buildings, and shopping centres.
In most of developing countries, due to warm climates, natural ventilation is
preferred via open windows and by fans. Thus the quality of indoor air depends
to a lesser extent on the indoor sources and more on the quality of the outdoor
environment. The outdoor quality is also worsening due to an increased number
of industries and vehicles. To minimize the pollution effective control measures
are to be taken, to protect human exposure to these pollutants both from
outdoors as well as from indoor sources. To address this problem of national
significance two important issues need to be addressed and are as follows:
a) Indoor air quality monitoring
b) Indoor air quality control
a) Indoor air quality monitoring:
A passive sampler is a device which is capable of taking samples of gas or
vapour pollutants from the environment at a rate controlled by a physical
process such as diffusion through a static air layer (therefore the expression
of diffusive sampling is used frequently) which does not involve the active
movement of the air through the sampler. The large and ever-growing number
of pollutants makes it difficult to associate health and comfort problems with
specific compounds. To conduct large studies, passive sampling is a suitable
technique as it is a simple, reliable and cost effective method. Due to the light
weight, the samplers are portable and they are often reusable and inherently
safe for use in flammable atmosphere. In principle sampling requires no pump
and it makes no noise. With the active sampling methods the sample is drawn
from a limited time only. Thus by using active sampling only concentration for
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3. the particular time of sampling can be obtained. Therefore, subsequent active
sampling can favorably be used to determine peak exposure in real
atmosphere with fast variations in concentrations. Diffusive samplers adsorb
the pollutants (several days to several weeks) of the entire study period and
thus can be used for the risk assessment studies of long term exposure. In
the past, most validation studies for diffusive sampling have dealt with the
analytes, concentration levels and sample composition encountered in
ambient and workplace air.
b) Indoor Air Quality Control:
The three strategies (in order of effectiveness) for reducing pollutants in
indoor air are source control, ventilation, and air cleaning. Source control
eliminates individual sources of pollutants or reduces their emissions, and is
generally the most effective strategy. Some sources, like those that contain
asbestos, can be sealed or enclosed; others, like combustion appliances, can
be adjusted to decrease the amount of emissions. Unfortunately, not all
pollutant sources can be identified and practically eliminated or reduced.
Ventilation brings outside air indoors. It can be achieved by opening windows
and doors, by turning on local bathroom or kitchen exhaust fans, or, in some
situations, by the use of mechanical ventilation systems, with or without heat
recovery ventilators (air-to-air heat exchangers). However, there are practical
limits to the extent ventilation can be used to reduce airborne pollutants.
Costs for heating or cooling incoming air can be significant, and outdoor air
itself may contain undesirable levels of contaminants. Air cleaning may serve
as an adjunct to source control and ventilation. However, the use of air
cleaning devices alone cannot assure adequate air quality, particularly where
significant sources are present and ventilation is inadequate.
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4. Air Cleaners as effective control measure
Indoor air pollutants are generally of three kinds viz.; particulate, gaseous
and radon and its progeny. Gaseous pollutants have been discussed briefly
herein.
Gaseous pollutants include combustion gases and organic chemicals
which are not associated with particles. Hundreds of different gaseous pollutants
have been detected in indoor air. Sources of combustion gases (such as carbon
monoxide and nitrogen dioxide) include combustion appliances, cigarette
smoking, and the infiltration of vehicle exhaust gases from attached garages or
the outdoors. Gaseous organic compounds may enter the air from sources such
as cigarette smoking, building materials and furnishings, and the use of products
such as paints, adhesives, dyes, solvents, chaulks, cleaners, deodorizers,
personal hygiene products, waxes, hobby and craft materials and pesticides.
Air cleaners are usually classified by the method employed to remove
particles of various sizes from the air. There are three general types of air
cleaners in the market: mechanical filters, electronic air cleaners, and ion
generators Devices such as air conditioners, humidifiers, and dehumidifiers may
technically be considered air cleaners because they may reduce some pollutants
present in indoor air through condensation, absorption, and other mechanisms.
The addition of adsorbents such as carbon, zeolite and potassium
permanganate will assist an air filter in removing various gasses and odors from
the air by adsorbing these gasses into the media or through a process called
chemisorption. Activated carbon has incredible porosity and a large and highly
active surface area. One pound of activated carbon has the surface area equal to
125 acres. The activated carbon filter works by adsorption and physical
screening of contaminants. The carbon adsorbs gaseous molecules by physically
binding them to the porous structure. Activated carbon is best suited to remove
compounds with high molecular weight such as volatile organic compounds
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5. (V.O.C.s) like benzene, toulene and xylene. Zeolites are a class of a naturally
occurring minerals derived from volcanic ash. Zeolites can also be reproduced
synthetically because of their consistent and predictable porous structure. One
gram of zeolite can have up to several hundred square meters of surface area.
These minerals are effective at removing V.O.C.s and ammonia compound
odors. Like carbon, gasses are trapped in the voids of the porous zeolite
structure. Chemisorbents work through binding gasses and a chemical reaction
process. These odor control substances are best for the removal of low
molecular weight gasses such as formaldehyde, ammonia and hydrogen sulfide.
A binder such as activated alumina is impregnated with Potassium
Permanganate to create a chemically active media. This non-toxic media first
physically traps selected gas molecules and then chemically destroys them
through a process called oxidation .This oxidation process is media based and
no oxygen or ozone is generated. The effectiveness of odor removing media is
related to the amount and type of gasses present in the air and the quantity and
depth of the adsorbent material and the velocity of the air traveling through the
media. The location of the odor adsorbing media relative to the particle filtration
media is also important. If the odor adsorbing media is placed first, then particles
in the air will cover the porous structure of the odor adsorbing media and reduce
its effectiveness at trapping odors.
The effectiveness of air cleaners in removing pollutants from the air
depends on both the efficiency of the device itself (e.g. the percentage of the
pollutant removed as it goes through the device) and the amount of air handled
by the device. For example, a filter may remove 99% of the pollutant in the air
that passes through it, but if the air flow rate is only 10 cubic feet per minute
(cfm), it will take a long time to process the air in a typical room of 1000 cubic
feet. Although there is no universally accepted method for comparing air-cleaning
devices, several investigators of portable air-cleaning units have expressed their
results as a "clean air delivery rate" or CADR. The CADR is the product of the
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6. unit efficiency and the air flow rate, and is a measure of the number of cfm of air
it cleans of a specific material.
The factors for selection of indoor air cleaner include the following:
a Estimated capital and maintenance cost
* Installation requirements (e.g. power, access)
* Possible production or redispersal of pollutants such as ozone,
particles formulated and trapped gaseous pollutants
a Possible health effects
a Potential effectiveness of the device under the existing conditions
tv Need for routine maintenance including cleaning and replacement of
filters and sorbent.
The various factors influencing efficiency of filters include:
•ft Air flow rate through the sorbent
a Concentration of the pollutants
a Presence of other substances or vapors (e.g. humidity)
Physical and chemical characteristics of both the pollutants and the
sorbent (e.g. weight, polarity, size and shape)
•ft Configuration of the sorbent in the device
a. Quantity of sorbent used and the sorbent depth
Conclusions
Indoor air pollutants can be grouped into three categories viz; particles,
gaseous pollutants and radon and its progeny. Passive sampling appears to be
technically feasible option for monitoring indoor air pollutants. Zeolites are
proving to be the adsorbents of choice for many cost effective air pollution control
technologies treating the hazardous air pollutants and listed VOCs. The need for
technologically improved air purification systems has been indicated by keen
client interest in the use of zeolites in controlling indoor air pollutants. The issues
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7. to be addressed are the types of air cleaners available to the consumer,
effectiveness of air cleaners in removing indoor air pollutants, factors to consider
in deciding whether to use an air-cleaning unit etc.
1 7 R
8. Reference:
1. Humphreys MP 1987. Performance testing of residential indoor air cleaning
devices. Presented at the 1987 EPA/APCA Symposium on Measurement of
Toxic and Related Air Pollutants, Research Triangle Park, NC, May 3-6, 1987
2. National Academy of Science. 1981. Indoor pollutants, Washington, DC :
National Academy Press.
3. Wadden RA, Scheff PA. 1983. Indoor air pollution. New York : John Wiley
and Sons
4. Ramanathan K, BeblerVL, Kosuko M, Sparks LE. 1988. Evaluation of control
strategies for volatile organic compounds in indoor air. Environmental
Progress 7(4): 230-235.
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