Page 433 - Fundamentals of Air Pollution 3E

III. Indoor Air Pollutants 385

The air exchange rate influences the concentration of indoor pollutants
in two ways. At higher air exchange rates, the pollutants inside a structure
are removed from the interior. As long as the ambient outside air has
lower pollutant concentrations, high exchange rates help lower indoor air
pollutant levels. However, if the pollutant concentration outside is elevated,
then an increase in the air exchange rate will bring these materials into the
building; e.g., an idling vehicle adjacent to an air intake will transfer exhaust
fumes into the building. At lower exchange rates, pollutants released from
sources inside the building can contribute to higher levels of indoor pol-
lutants.
The concentration of indoor pollutants is a function of removal processes
such as dilution, filtration, and destruction. Dilution is a function of the
air exchange rate and the ambient air quality. Gases and particulate matter
may also be removed from indoor air by deposition on surfaces. Filtration
systems are part of many ventilation systems. As air is circulated by the
air-conditioning system it passes through a filter which can remove some
of the particulate matter. The removal efficiency depends on particle size.
In addition, some reactive gases like NO 2 and SO 2 are readily adsorbed on
interior surfaces of a building or home.

III. INDOOR AIR POLLUTANTS.

Table 23-1 shows the major categories of indoor air pollutants and
sources. Table 23-2 shows a summary of reported indoor air pollutant
concentrations compiled by the U.S. Environment Protection Agency. Infor-

TABLE 23-1
Indoor Air Pollutants and Typical Sources

Pollutant Source
Combustion gases — CO, NO Combustion — furnace, cooking stove, space heater,
etc.
Volatile organic compounds (VOCs) Outgassing of building materials, coatings, wall and
floor coverings, and furnishings
Formaldehyde Outgassing of pressed wood, insulation foam
Pesticides Household products
Particulate matter Combustion
Biological agents — molds, spores, Contaminated ventilation systems, pets
dander
Environmental tobacco smoke Smoking in building
Radon Infiltration from soil beneath structure
Asbestos Construction coatings, tile, insulation