cockroaches and other pests (all of which can be allergenic) in the indoor environment
(NAS 2004).
CHANGES IN BUILT ENVIRONMENT
The characteristics of the built environment play a major role in determining
indoor air quality. These factors include insulation, HVAC type, air exchange rates,
building materials, building type, and numerous other factors. The majority of the world’s
population now resides in cities and the rate of growth of cities is expected to outpace
the rate of growth of less urban areas (United Nations 2010). The influx of people into
cities as well as the continued build-up of the urban environment increases the need for
higher density housing that will in turn increase the number of multi-tenant buildings. In
addition to changes in the built environment in response to direct environmental
pressures (e.g., increased temperature, humidity, etc.) and population driven housing
demand, global climate change will exert a significant impact on indoor air quality
as a result of changes in home construction practices (e.g., energy efficiency,
etc.) intended to reduce our carbon footprint.
Increased Air Conditioner Usage
The Department of Energy’s U.S. Energy Information Administration reports that
the percentage of homes with central air conditioning has grown from 23% in 1978 to
47% in 1997 (DOE 2010). By 2007, the U.S. Census Bureau reported that over 86% of
the occupied homes in the United States had some form of air conditioning (U.S.
Census Bureau 2008).
Weatherization and Energy Efficiency
EPA (2010) websites state that “Weatherization and other energy efficiency
upgrades can have negative impacts on occupant health and safety if not accompanied
by appropriate indoor air quality - IAQ - protections.” The EPA indicates that these
negative impacts include increased carbon monoxide, tobacco smoke, and hundreds of
volatile organic compounds, etc. Methods to increase air exchange rates such as
providing a small percentage of outdoor make-up air for HVAC applications has the
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