Approaches for Estimating Personal Exposure to NO2 across Melbourne
Estimating an individual’s exposure to a pollutant by using a daily ambient concentration averaged across a city contains assumptions that are not strictly true. Firstly, air quality on any day is not uniform across a city, i.e. there are spatial (and temporal) gradients, and secondly, many people do not remain in one location over the study period, be it one day or one year or more.
This paper presents results from the modelling component of a DEH-funded study to investigate the degree to which modelling, taking into account spatial variation and micro-environments, can contribute to estimates of personal exposure across a city. Cumulative exposure to NO2 over four 2-day periods was measured across Melbourne by 15 participants wearing passive samplers. Time-activity diaries were kept and simultaneous indoor and outdoor measurements were made while participants were at work and at home, and in vehicles. The measurements were performed twice in both winter 2005 and summer 2006. The study also developed a conceptual model of indoor exposure to NO2 based on activity information and location/dwelling characteristics.
The Australian Air Quality Forecasting System AAQFS and the air quality model TAPM-CTM were run for each two-day event, and hourly gridded NO2 fields used to calculate the cumulative ambient exposure for each trip profile. In this paper, the measured personal exposures for the two winter events are compared to various computed exposure sets involving measured and modelled concentrations, the conceptual model of indoor exposure, and predictions from a near-road model.