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

HUMAN EXPOSURE TO AIR POLLUTION
periods of time involves major logistical complications, the relationship between
long-term ambient air pollution concentrations and long-term average personal
exposures is difficult to assess. Studies that have compared average personal exposures
of people from different countries or communities, with different average
outdoor air pollution concentrations, however, generally show that those
in the countries/communities with the highest ambient concentrations had the
highest personal exposures and vice versa (28,46). Central-site long-term average
outdoor concentrations should therefore reflect with sufficient accuracy the
differences in average personal exposures between communities, again especially
for homogeneously distributed air pollutants (such as fine particles) that penetrate
well from outdoor to indoor environments. In a study in seven American
cities, for example, indoor particle concentrations were about twice as high as
outdoor concentrations. The effect of indoor sources, however, was found to be
similar in all cities, implying that differences in indoor concentrations between
the cities are mainly caused by differences in outdoor concentrations (47). For
air pollutants with high spatial variability, such as traffic-related pollutants, the
correlation between personal and central-site outdoor concentrations is lower,
but measurements or estimates of outdoor concentrations just outside the home
are more strongly related to personal exposures. Individual activity patterns (e.g.
time spent in traffic), however, can significantly influence personal exposures independently
of residential outdoor concentrations.
Much of the research on the relationship between personal or indoor and outdoor
air has been conducted in Europe and North America. Less is known about
these relationships in other parts of the world. Given the considerable differences
in sources of pollution, location of pollution sources with respect to populations,
habitation patterns and building characteristics, the relationship could vary substantially
across regions. A study conducted in Bangkok, however, also suggested
that ambient monitors were able to capture the daily variation in indoor PM10
levels (18). A personal exposure study of children living in Santiago de Chile also
showed strong cross-sectional associations between personal, indoor and outdoor
PM2.5 levels. Correlations for nitrogen dioxide were weaker, probably owing
to the presence of gas cooking stoves in all homes (48). A study in four Mexican
cities, however, did show that the best predictors of personal nitrogen dioxide
exposure were outdoor levels and time spent outdoors (49). In the absence of
strong indoor sources, personal–outdoor correlations could actually be stronger
in relatively polluted locations, since elevated ambient levels may obscure the influence
of non-ambient sources and increase the relative contribution of outdoor
particles to personal exposure (48).
Population characteristics
While exposure assessment can be used to estimate exposures experienced by the
“average” individual, it is often used to address populations most likely to be at
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