Environmental Engineering Reference
In-Depth Information
For the workplace, a constant indoor-outdoor ratio was used for all workplaces
and was the mean value measured in the study (0.74).
When used in Eq. 1, nearly all combinations led to personal exposure estimates
in good agreement with the measured 48-h personal exposure values, especially by
the criterion that a prediction method is deemed to be valid if the root mean square
error (RMSE) is less than the standard deviation of the measurements. Importantly,
the standard deviations predicted by these spatial-variation techniques match well
with the variation seen in the measurements. However there was a hierarchy of
skill amongst the methods. For example, the two methods that assign an I/O ratio
according to home characteristics consistently produced better statistical results
than that which assigns the same mean ratio to everyone. The mass balance
method was more accurate than the gas cooking method, especially for the RMSE
and correlation statistics.
As far as the three approaches for calculating the ambient outdoor concentration
are concerned, the blended approach led to better personal exposures than the
nearest monitor approach with respect to RMSE and correlation, but was slightly
inferior for mean value and standard deviation. However, results from both were
more than satisfactory. All statistics were poor for the method in which the personal
exposure was calculated by assigning to each participant the mean monitor
concentration scaled by the mean measured ratio, and this approach is clearly
inferior to the techniques developed in this project. It must also be remembered
that there is no exposure variation between participants using this mean monitor
concentration method, whereas the standard deviation predicted by the spatial
variation techniques matched well the variation seen in the measurements.
3. Summary and Discussion
Our research has identified a simple NO 2 personal exposure methodology that
could be widely applied, without the need for access to air quality models and
with only minimum information from respondents. It is recommended that best
results would be obtained with the I/O ratio calculated from a mass balance
method. This requires participants only to record daily gas cooking periods and
approximate house age. For simplicity's sake, the recommended method for
calculating the required ambient outdoor concentration is to use the nearest
monitor approach instead of the blended approach.
Strictly speaking, the findings can only be related at this stage to NO 2 and to
the existing EPA Victoria monitoring network, although it is expected that the
methodology would also be valid for cities with monitoring networks of similar
density to that of Melbourne. Our sample size for NO 2 was necessarily limited to
a total of 24 volunteers, with between 15 and 17 participating in each of the
4 events. However our methodologies showed skill for each event, as well as for the
combined data set involving 59 samples. Repetition of our work, ideally in another
city and with a higher number of participants, is highly desirable and would
Search WWH ::




Custom Search