Environmental Engineering Reference
In-Depth Information
2. Findings
Methodologies for estimating personal exposure that were evaluated in this study
included three approaches to calculating ambient exposure and three methods of
estimating indoor-outdoor ratios. Ultimately it is hoped that our recommended
methodology can be used in epidemiological studies where pollutant exposure of
many subjects needs to be estimated. To this end, we introduced two simplific-
ations. Firstly, following our finding that the major personal exposure components
occur in the home and work environments, we omitted the transit environment
from our model. Secondly, recognising the practicalities of an epidemiological
study, we assumed that all participants were at home between 1800 Eastern
Standard Time (EST) and 0800 EST, and at work between 0800 EST and 1800
EST.
Estimates of personal exposure for each participant were calculated as a time-
weighted sum of the mean ambient concentrations during the home and work
periods, scaled by respective I/O concentration ratios. Ambient NO 2 exposures for
each person for these periods were obtained by three methods:
Concentrations at the nearest monitor in the EPA Victoria ambient monitoring
network to home or work were assigned
Concentrations at the home and workplace were assigned from the gridded
hourly NO 2 concentrations obtained by blending modelled and EPA Victoria
monitored data
Details of this blending approach using simulations from a complex air quality
model can be found in Physick et al. (2007). In epidemiological studies, the
exposure assigned to all urban dwellers over a period is often the mean pollutant
concentration for that period, averaged over all monitors in the urban monitoring
network. For comparison with our two methodologies above, we also evaluated a
third approach to estimating ambient concentration:
For each event, the mean concentration across all monitors in the network
was assigned to each participant
Home indoor-outdoor ratios were calculated from two methods for computing
indoor NO 2 concentrations, developed from the measurement program. These
methods can be summarised as:
Mass balance . Applying the steady state mass balance equation, the indoor
NO 2 concentration is calculated using activity and house characteristics with
an outdoor (ambient) concentration. Then it is straightforward to calculate
the I/O ratio.
Gas cooking . One of two indoor-outdoor ratios is assigned to each home
according to whether a gas cooking appliance is installed (0.67) or not (0.47).
These mean values are obtained from measurements in the current study.
Also, the use of measured indoor-outdoor concentration ratio averaged
across all homes for each participant was evaluated.
Mean measured ratio . The I/O ratio used is the mean value from all homes
measured in this study (0.57).
 
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