Environmental Engineering Reference
In-Depth Information
7.4 Estimates of Personal Exposure to NO
2
Using
Ambient Concentrations and Activity Data
Bill Physick, Jennifer Powell, Martin Cope, Kate Boast, and Sunhee Lee
CSIRO Marine and Atmospheric Research, PB1, Aspendale, Victoria, 3195, Australia
Abstract
This paper presents results from a study to investigate the extent to
which NO
2
data from ambient network monitoring, air quality modelling, or a
combination of both, can improve estimates of personal exposure across a city. As
it is not practical to measure the personal exposure of every individual, a common
assumption in most epidemiological studies for urban areas has been that people
are exposed to a spatially-homogenous pollutant, ignoring variations in concentrations
across an airshed and in various micro-environments.
Our conceptual model of an individual's personal exposure to NO
2
is based on
time-weighted sums of exposure in the microenvironments of home, transit and
work. Personal exposure in each microenvironment is linked to ambient concentra-
tion by indoor-outdoor concentration ratios. To allow us to both develop and eva-
luate the model, we designed a measurement program involving volunteers across
Melbourne wearing personal passive samplers. Participants also wore additional
samplers for sub-periods of each 48-hour exposure, at home, at work and in transit.
Diaries were designed to record details of time and activities in each micro-
environment, especially those associated with cooking and ventilation.
Three methods of estimating indoor-outdoor ratios and three approaches to
calculating ambient exposure were evaluated. For estimation of the personal expo-
sure to NO
2
of a large number of people, it is recommended that best results would
be obtained with the I/O ratio calculated from a mass balance method. This
requires participants to record daily gas cooking periods and approximate house
age, although a simpler but slightly less accurate method dependent only on the
existence or not of a gas cooking appliance also produces satisfactory results. The
recommended method for calculating the required ambient outdoor concentration
is to use values from the network monitor nearest to a person's microenvironment.
Evaluation statistics were considerably poorer for a commonly-used method
whereby each person is assigned the same ambient concentration, taken to be the
mean concentration across all network monitors.
Keywords
Personal exposure, passive NO
2
samplers, spatial variation, indoor-
outdoor concentration ratio
