Air Quality Guidelines Global Update 2005 - World Health ...

HUMAN EXPOSURE TO AIR POLLUTION
both exposures from outdoor origin and indoor sources) or only in that part of
the exposure that is from outdoor origin. For pollutants such as benzene (where
no constituent differences exist and the toxicity of outdoor and indoor exposure
is the same) optimal exposure-based air quality management would in some cities
point to ambient sources and in others to indoor sources (even consumer
products), depending on which sources dominate the personal exposure (4). For
PM, however, the composition of particles of outdoor origin can be very different
from that of particles from indoor sources. Methodological investigations
have therefore pointed out that ambient and non-ambient exposures need to be
considered as two separate classes of pollutant (36,37). Ebelt and colleagues (38)
developed separate estimates of exposure to ambient and non-ambient particles
based on time–activity data and the use of particle sulfate measurements as a
tracer for indoor infiltration of ambient particles, and evaluated their relative effect
on cardiopulmonary health. Although total and non-ambient particle exposures
were not associated with any of the health outcomes, ambient exposures
were associated with reduced lung function, lower systolic blood pressure, increased
heart rate and increased supraventricular ectopic heartbeats. These results
obviously do not imply that non-ambient exposures cannot have health effects
of their own in other settings.
Since people spend most of their time indoors, most of the exposure to pollution
of outdoor origin takes place indoors, where exposure can be modified by
the building and its equipment (e.g. air conditioning). If one is primarily interested
in pollutants of outdoor origin, indoor concentrations are of interest only
in so far as they reflect or do not reflect outdoor concentrations and sources. This
concept has been most advanced for particle exposure, but can apply to other
components with significant indoor sources as well, provided that it is not the
pollutant per se that is causing the health effects. From a policy perspective, however,
interventions based on reducing specific indicator pollutants that are not
necessarily directly related to health may not result in the most effective strategies.
For example, it remains unclear whether the observed association between
nitrogen dioxide and health is due to the nitrogen dioxide itself or whether nitrogen
dioxide is an indicator of other correlated pollutants, such as ultrafine particles
and traffic-related pollution in general (3).
Reduction of pollution generated indoors
One of the most practical ways of reducing exposure to indoor sources of air pollution
has been the outdoor dissemination of indoor sources of pollution. For example,
while chimneys do not change the quantity of smoke emitted, they reduce
indoor exposures to smoke substantially.
Indoor sources can make a substantial contribution to outdoor concentrations
in places where there are large, widespread sources of indoor air pollution. For example,
the infamous London Fog was caused essentially by indoor use of coal for
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