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Indoor Air Pollution

Thomas G. Robins, MD, MPH

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Why the Emphasis on Indoor Air?

In recent years, the problem of indoor air pollution in residential, office, and public buildings has come into sharp focus. Concerns about the potential health effects of indoor air pollution stem from the following three observations: 1. The levels of some pollutants are higher indoors than outdoors,

in some cases exceeding the national standards set for exposure outdoors.

2. Urban populations typically spend more than 90% of their time indoors; the single most important indoor location is the home, where individuals spend about 70% of their time.

3. It is the most susceptible groups—the young, the elderly, and the infirm—who spend the greatest amount of time indoors.

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Time Spent in Locations: Indoors & Outdoors

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Indoor Air Versus Outdoor Ambient Air

There are several factors that differentiate indoor air from outdoor ambient air enclosed air has less dilution, which may be

variable over time population affected is usually in proximity to the

source or sources multiple contaminants complicate methods to

analyze and mitigate the hazards of indoor air pollution

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Sources of Indoor Air Contaminants

Types of sources of indoor pollutants include: infiltration from the outdoor air release from the building and its contents generation by human activity

The indoor concentration of any given air pollutant depends on: the type of source The strength of the source (rate of generation) rate of removal or accumulation in the enclosure

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Sources of Indoor Air Contaminants

A variety of construction materials, furnishings, and consumer products containing volatile chemicals provide sources of indoor contaminants Synthetic organic materials are associated with

emissions from walls, ceilings, carpets, draperies, plastics, paints, pesticides, cleaning materials, and personal and household products

Use of cheap fuels in home fireplaces, wood burning stoves, and unvented kerosene space heaters has increased the indoor concentration of volatile organic compounds and such combustion products as carbon monoxide, sulfur dioxide, and nitrogen dioxide

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Hazards of Energy Efficient Buildings The worldwide energy crisis in 1973-1974 contributed to the

problem of indoor air pollution through efforts made to conserve fuel in commercial and residential buildings As older buildings became better insulated and newer buildings were

built with a thermal envelope, less fresh air was allowed to infiltrate into the structures.

The natural ventilation provided by opening windows was replaced by mechanical ventilation in most new office buildings; to further conserve energy, ventilation systems were often operated conservatively

homes were caulked, weatherstripped, and sealed The old-fashioned "leaky" home or office building with open windows,

having a complete exchange of air every few hours, was replaced by energy-efficient buildings and homes having greatly reduced ventilation rates

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Fresh Air Exchange Rates

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Lack of Regulation

In contrast with situation for ambient (outdoor) air quality standards, to date, no national government strategy exists to provide a coordinated approach to ensure adequate indoor air quality

In part this reflects the inherent differences in the problems of ambient versus indoor air pollution: all members of a community are provided with the same

ambient air in indoor environments, the situation varies considerably,

especially in private residences, where the costs and benefits of both pollution control and pollution prevention are internalized within individual households

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Lack of Regulation

There is a lack of general indoor air quality standards in the workplace and in the service sector manufacturing sector is governed by occupational regulations,

such as source control, ventilation requirements, and personal protective equipment

nonmanufacturing office environment is not governed by any standards, as occupational standards are neither applicable, relevant, nor appropriate

no standards in place covering exposure to the general public in the service sector, such as theaters, hotels, transportation facilities, recreational facilities, businesses, hospitals, or schools

only exceptions are a few product-specific prohibitions such as urea foam formaldehyde and cigarette smoke

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Types and Sources of Indoor Air Pollutants Indoor air pollutants can be categorized by type of

source, such as combustion, and by pollutant group, such as volatile organic compounds (VOCs) and fibers Sources can be further characterized by pollutants

emitted, by locations, and by rate and pattern of emissions The following discussion of indoor air pollutant sources

and effects is based on the following classification: (1) combustion products; (2) volatile organic compounds (VOCs) and formaldehyde; (3) microbiologic agents; (4) environmental tobacco smoke (ETS); and (5) radon

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Common Indoor Air Pollution SourcesTable 2 — Common Indoor Air Pollution Sources and Pollutants in the Home and in

Commerical Buildings*

Source Pollutant

Tobacco smoking Carbon monoxide Particles Organics

Standing water Biologic contaminants (eg, Legionella, molds)

People Carbon dioxide Odors (bioeffluents) Bacterial & viral contaminants

Furnishings, building material Formaldehyde Organics (eg, solvents) Asbestos

Computers, copiers, fluids, typesetting equipment

Organics Particles

Garages, loading docks Carbon monoxide Particles Organics

Outdoor air Oxides of carbon, nitrogen, sulfur, Particles, organics, pollen, allergens

Solid gas Radon, biocides, organics

Gas boilers, furnaces, cookers, ranges, unvented, kerosene heaters, space heaters, coal/wood stoves

Carbon monoxide, nitrogen dioxide Particles, organics

Solvents, paints, glues, resins, personal care, and household products

Organics

*Adapted from American Thoracic Society, 1990.

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Combustion Sources The principal combustion sources indoors include

tobacco smoking, which generates environmental tobacco smoke (ETS); unvented combustion appliances; and wood stoves and fireplaces combustion sources emit inorganic gases (NO, NO2, CO, CO2) and

particulates depending on fuel type and pyrolysis conditions, combustion sources

can also emit hydrocarbon gases, vapors, and organic particles most liquid and solid fuels contain impurities or additives that may

result in emissions of metals, mercaptans, sulfur oxides, or particles as the fuels burn

gas appliances may emit very small particles, in the sub-micron range, as may burning tobacco products

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Combustion Sources Unvented gas combustion is a ubiquitous source of nitrogen dioxide

and carbon monoxide in residences almost half the homes in the United States have gas stoves many studies indicate that gas ranges can raise indoor nitrogen dioxide

concentrations above ambient levels gas ranges emit carbon monoxide at about 10 times the rate of nitrogen

dioxide, but under typical conditions, concentrations do not exceed 10 ppm

about 11% of the US population potentially are exposed to gas or kerosene space heater emissions emissions include particles, carbon monoxide, and nitrogen dioxide, plus

sulfur dioxide if sulfur-containing fuel is burned in one survey of homes in Connecticut, the sulfur dioxide levels were less

than 2 µg/m3 inside homes without kerosene space heaters, but 60 to 150 µg/m3 in homes where such heaters were operated

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Environmental Tobacco Smoke (ETS)

The burning of tobacco products is a ubiquitous source of a large number of indoor contaminants tobacco burning produces a complex mixture of gases, vapors, and

particulate matter: more than 4,500 compounds have been identified, about 50 being known or suspected carcinogens

the number of smokers and the pattern of smoking determine the source strength for generation of ETS

the concentrations of ETS components to which nonsmokers are exposed depend further on the degree of dilution of the smoke

in smoky bars, waiting areas, restaurants, automobiles, airplanes, or even in the home, short-term concentrations of ETS can be high: concentrations of particles of respirable size in rooms contaminated by ETS can range from 100 to more than 1,000 µg/m3

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Comparison of PM10 and PM2.5 Levels (ug/m3) in Homes with Versus without Cigarette

Smokers: Detroit

PM10 PM2.5Smoking Non-smoking Smoking Non-smoking

24-hour 63.0 + 62.1 35.7 + 22.0 42.5 + 18.8 23.5 + 19.2

16-hour 67.1 + 31.3 32.2 + 23.7 51.0 + 29.7 18.2 + 14.3

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Volatile Organic Compounds

Modern furnishings, construction materials, and consumer products contaminate indoor air with numerous volatile organic compounds (VOCs) sources include home-care and building maintenance materials such as

disinfectants, room deodorizers, carpet shampoos, cleaning solutions, furniture polish, and floor waxes, moth crystals, fabric care products, and cosmetics

hobbies that call for the use of volatile hydrocarbons may at times increase exposures far beyond industrial guidelines

Studies of VOCs found indoors reveal a vast array of aliphatic, halogenated, and aromatic hydrocarbons, alcohols, ketones, and aldehydes: in a recent Environmental Protection Agency (EPA) study of air quality in 10 public access buildings, more than 500 VOCs were identified.

Many VOCs have been found to have levels higher indoors than outdoors