Measurements of personal exposure to NO2 and modelling using ambient concentrations and activity data

This study was undertaken with the aim of estimating true personal exposures from data that are less costly and more easily obtained than in detailed measurement programs. We present an evaluation of simple methodologies for estimating true personal exposure to nitrogen dioxide (NO2) that take into account spatiotemporal variability in ambient concentrations across urban areas and which link the latter to personal exposure through indoor/outdoor (I/O) ratios determined from time-activity diaries. To allow us to both develop and evaluate the methods, we designed a measurement program involving volunteers across Melbourne wearing personal passive samplers. Three methods of estimating indoor–outdoor ratios and three approaches to calculating ambient exposure, including network monitors and the complex air quality model TAPM-CTM, were evaluated. All methods except one produced good agreement with the measured values. Importantly, the percentile statistics and standard deviations predicted by these spatial-variation techniques matched well the distribution seen in the measurements. For the best estimates of personal exposure to NO2, it is recommended that the I/O ratio be calculated using a mass balance method, requiring participants to record daily gas cooking periods and approximate house age. The recommended method for calculating the required ambient outdoor concentration is to use values from the network monitor nearest to a person’s microenvironment. Our research has identified a simple exposure methodology that could be widely applied for epidemiological cohort studies and population exposure estimates in urban areas with fixed monitoring networks, with only minimum information from respondents.