Environmental Engineering Reference
In-Depth Information
However, the intake fraction per unit time and per individual in traffic is actually
larger compared to that of residents and others. Thus, if the time spent in each of
these microenvironments was equal per person, exposure in traffic would be
responsible for the greater part of the intake fraction.
The intake fraction results from both modeled and measured data are in the same
order of magnitude and are generally within an order of magnitude range of those
found in the most previous mobile source intake fraction studies.
Conclusion
Intake fraction is useful measure to evaluate and compare different sources catego-
ries that can be used a health decision support tool. Assuming that the spatial and
temporal patterns of emissions and population activity remain unchanged in differ-
ent emission scenarios, the calculated intake fraction allows for direct estimate of
total population exposure in all these scenarios. We evaluated the benzene traffic
related emission intake fraction for the MHA for different domains and years.
The spatial variation of the intake fractions and especially the very detailed calcula-
tions for the smallest domain, street canyon, demonstrate clearly how crucial it is to
have access to detailed information on traffic patterns and locations and activities
of the people in order to get a reliable estimate on the real burden of pollutants on
human exposure and health.
The highest values of 100 × 100 m 2 grid cell iF's (10 −10 -10 −7 ) are concentrated
in residential and commercial areas where the density of receptors and sources is
higher. In other words, between 0.1 ng and 0.1 mg are inhaled in each 100 × 100 m 2 grid
cell per gram of benzene emitted from mobile sources in the whole HMA. The intake
fraction of the same population summed across these different microenvironments
in the HMA is 10 −5 . Population exposure to benzene was higher during commuting
due to higher concentrations in the vicinity of the streets as well as inside vehicles.
The same population is also exposed at home and workplace as a result of spending
a large fraction of time indoors.
References
1. Bennett D, McKone T, Evans J, Nazaroff W, Smith K, Margni M (2002) Defining intake
fraction. Environmental Science and Technology 36:206A-211A
2. Bennett D, Margni M, McKone T, Jolliet O (2002) Intake fraction for multimedia pollutants: a
tool for life cycle analysis and comparative risk assessment. Risk Assessment 22(5):905-918.
3. Kousa A, Kukkonen J, Karppinen A, Aarnio P, Koskentalo T (2002) A model for evaluating
the population exposure to ambient air pollution in an urban area. Atmospheric Environment
36:2109-2119
4. Karppinen A, Kukkonen J, Elolähde T, Konttinen M, Koskentalo T (2000) A modelling
system for predicting urban air pollution: comparison of model predictions with the data of an
urban measurement network in Helsinki. Atmospheric Environment 34:3735-3743
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