The effect of population-scale human activity patterns on exposure to air pollution

Abstract

Introduction. Exposure is often estimated only at the patient home address, inherently suggesting that subjects stay near their residence throughout the day. Methods. We studied exposure to nitrogen oxides of large groups of individuals by anonymously tracking their location during the day. Differences in exposure at the home address and while accounting for the time spend at work/school were studied. Geocoded residence and school addresses of 1.5 million schoolchildren age 6-18 and of the workplace of 400,000 adults were obtained from the Israeli Central Bureau of Statistics. Air pollution levels for 2008 were obtained using two models: a stationary nationwide land use regression model for NOx concentrations (250 m grid resolution), and a dynamic optimization dispersion model that provides half-hourly NO2 concentrations (500 m grid resolution) over smaller spatial extent but accounts for the spatiotemporally varying emissions and wind field. Results. (1) Due to daily varying NO2 concentrations, differences of 6-20 ppb were evident between the residence place and the workplace/school microenvironments. For example, in the Tel-Aviv metropolitan area about 50% of the adults and 66% of the children were exposed to higher concentrations at home than at work/school. (2) Using annual average NOx exposure estimates (to isolate the spatial commute contribution from the temporal daily variation contribution), about 58% of the adults and 70% of children experienced only small (<5 ppb) differences in exposure between the residence and work/school. (3) Commuters (defined as adults (children) that live more than 10 (5) km away from their residence place) and non-commuters had a similar distribution of differences in exposure to NOx between the two microenvironments. Conclusions. Reliable exposure estimation requires accurate information on (a) time-activity patterns (here in terms of spatiotemporal location), and (b) the pollutant spatiotemporal variation.