Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
chemiluminescence monitors. The distance from each daycare centre to
the nearest monitoring site varied from 0.5 to 11 km.
The geometric mean of personal nitrogen dioxide exposure levels
of in the total 13-week period was 26.5 µg/m 3 in the downtown area
and 17.5 µg/m 3 in the suburban area. These exposure levels were
significantly lower than ambient air levels of nitrogen dioxide in the
same areas. Gas cooking stove or/and smoking at home significantly
increased personal exposure to nitrogen dioxide. The weekly exposures
averaged over all children in each daycare centre correlated poorly
with the fixed site ambient air levels ( r 2 = 0.37), but much better
with the nitrogen dioxide levels inside and outside the daycare
centres ( r 2 = 0.88 and 0.86, respectively). In the suburban and
downtown groups the between-child variances in nitrogen dioxide
exposures were only 14% and 28% of the total variances, which were
dominated by the within-child variances.
Stationary measurements at the ambient air fixed sites and inside
and outside the daycare centres explained the variations in personal
nitrogen dioxide exposures of the children well during the spring, but
not during the winter. A statistical model, where data from outside
daycare centre measurements, fixed ambient air monitors, residential
area and home characteristics (i.e., gas cooking stove, smoking inside
at home, type of dwelling) were included, explained only 32% of the
personal exposure variations in winter, but 67% in spring.
There were significantly more days with stuffed nose (26% versus
20%) and cough (18% versus 15%) in the downtown area than in the
suburban area. The observed risk of cough was highest and
statistically significantly increased compared to the levels of
personal nitrogen dioxide. Also, when using daycare centre
measurements or fixed site ambient air data for exposure assessment,
there was a positive trend between nitrogen dioxide exposure and cough
in winter these associations were, however, weaker and
non-significant.
According to the result of the study, exposure to nitrogen
dioxide should be measured using personal exposure measurements when
studying health effects of the gas in non-symptomatic children in
areas with low nitrogen dioxide levels. Even personal exposure
measurements using weekly averages, however, may not adequately
reflect all biologically relevant exposure, e.g., short-term peak
concentrations. The most significant determinants of the personal
nitrogen dioxide exposures of the children in Helsinki are living in
downtown rather than in a suburban area, gas versus electric cooking
stove and smoking in the home. However, even all risk factors together
did not increase the personal exposures of downtown children up to
suburban outdoor air levels.
12.3.4 Ozone
The UC Berkeley Ozone project (USA) is an example of an
epidemiological study addressing long-term effects of lifetime ambient
oxidant pollution on pulmonary function (Tager et al., 1998a,b). A
major purpose was to address the feasibility of improving ozone
exposure assignment by means of collecting lifetime information on
relevant time-activity patterns to exposure, in combination with fixed
site ambient air monitoring data. Individual factors considered to be
relevant for exposure were:
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