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

PARTICULATE MATTER
ambient air. The monitoring data indicate that some of the highest exposures to
PM2.5 are typically experienced in this setting (25).
While personal exposures to PM and its components are influenced by indoor
sources such as smoking and cooking, in addition to outdoor sources, there is
a clear correlation at the population level between ambient PM concentrations
and concentrations of personal exposure to PM of ambient origin over time, especially
for fine combustion particles. On a population level, concentrations of
personal PM exposure “track” ambient PM concentrations over time, although
the actual levels may differ. Thus, measurements of PM in ambient air can serve
as a reasonable proxy for personal exposure in time series studies based on shortterm
changes in ambient levels.
In short-term studies, the relationship between ambient concentrations and
personal PM exposures has been studied in numerous locations (Table 1). The
longitudinal correlation between ambient and personal PM varies from person
to person, depending on factors such as exposure to environmental tobacco
smoke and cooking emissions, and the infiltration characteristics of the home
(77,82,94). At the population level, however, the correlation between ambient
concentrations and personal PM exposure over time is fairly high, supporting
the use of ambient PM measurements in time series studies as an exposure indicator
reflective of day-to-day variation (70,84–86,89,91,94). Also, the correlations
with ambient concentrations increase if PM constituents with few indoor
sources, such as BS or sulfates, are used as indicators (70,82,95).
While few studies have directly addressed whether ambient long-term PM
concentrations are correlated with long-term personal PM exposure (96), it is
again important to distinguish between exposures to ambient and non-ambient
particles. Studies of long-term exposure pose the difficult logistical problem of
measuring personal PM exposure over long periods of time. Nonetheless, several
relevant studies can be cited. Analyses conducted of EXPOLIS study data
have suggested that long-term ambient PM concentrations are well-correlated
with the population average of a series of personal PM2.5 exposure measurements
(64). Early work from the Six Cities Study has shown that personal sulfate measurements
conducted in Watertown (low ambient sulfate) were much lower than
those conducted in Steubenville (high ambient sulfate) (97). This finding supported
the use of outdoor measurements as a personal exposure metric in this
long-term study (97).
Within-city spatial variability in PM concentrations and in concentrations
of specific PM components has also been demonstrated (98,99). This variability
in ambient concentrations has also been reflected in variability in exposures
between those residing in the urban core vs those residing on the outskirts of the
city (96,100).
Recent evidence has shown that exposures of people living near busy roads are
insufficiently characterized by air pollution measurements obtained from urban
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