Exposure to air pollution in the transport microenvironment: how important is short-term exposure to high concentrations, and what are the determinants of this exposure? Roy Colvile 1, Mark Nieuwenhuijsen 1, Tom Bentham 1, Alan Robins 2. 1 Department of Environmental Science and Technology, Imperial College Faculty of Life Sciences, London SW7 2BP, UK 2 Department of Mechanical Engineering, University of Surrey, Guildford GU2 5XH, UK Poster presented at the ISEE/ISEA Conference, Vancouver, August Contact: Further work: D ispersion of A ir P ollution and P enetration into the L ocal E nvironment DAPPLE is a £1.6M (€/US$2.4M) research project funded by the UK Engineering & Physical Science Research Council, to study the determinants of exposure to air pollution from outdoor sources at distances less than 1km in the urban environment. It combines fluid dynamics, urban meteorology, traffic microsimulation and exposure assessment, using field measurement, wind tunnel simulation, advanced and operational dispersion modelling. For further details, see This poster presents an overview of the work that feeds into a major new investigation of exposure to air pollution, focussing on short-range exposure to vehicle exhaust emissions. It aims to stimulate debate about how much detail is needed in exposure assessment, for environmental epidemiology as well as air quality management. Peak exposure at local hot-spots is much greater than elsewhere Figures show wind tunnel measurements of the time-averaged (left) and log 10 ratio of peak to average (right) air pollution concentration in a plume from a single grossly polluting vehicle near a city street canyon junction This kind of variability can result in exposure misclassification that is significant even for study of linear dose-response over 24 hours, but even more important if a threshold for effects exists over shorter times, where roadside or background measurements are used as surrogates for exposure. On-street measurements of road-user exposure to PM showed individual- level variability of magnitude comparable to the geometric mean. This is consistent with our studies of the large amount of variability in concentration over distances as short as 1 metre and times as short as 1 second. High resolution exposure assessment is important for air quality management as well as epidemiology Urban background or roadside fixed-point air pollution concentrations are relatively insensitive to local traffic reduction and control measures. Exposure is much more sensitive, including exposure to peak concentrations which could dominate public concern about air quality 4,5. PM source apportionment and composition are different at hot-spots compared with elsewhere The figure shows modelled exposure of a cyclist moving along a 5 km route in Central London 3. Note the imported (mostly sulphate) aerosol dominating at most locations, but the local (mostly carbon) dominance at congested locations. Indoor exposure in near-road buildings is strongly influenced by the detail of advection and turbulence processes close to the source The contribution of nearby streets to poor indoor air quality will be influenced by the relative contributions of (i) advection at street level, (ii) advection over the top of roadside buildings, and (iii) turbulent diffusion out of street canyons. The figure shows a configuration studied in detail 2 in the wind tunnel and using computation fluid dynamics modelling. References 1) Adams H S, M J Nieuwenhuijsen, R N Colvile., M A J McMullen, P Khandelwal, Fine particle (PM 2.5 ) personal exposure levels in transport microenvironments, London, UK. Science of the Total Environment 279(1 ‑ 3), 29 ‑ 44. 2) Scaperdas A S, PhD Thesis, Imperial College, University of London. 3) Gomez-Perales J E, R N Colvile, M J Nieuwenhuijsen, Use of dispersion modelling to assess road-user exposure to PM 2.5. Atmospheric Environment submitted. 4) Colvile R N and D.A.P.P.L.E. Project Co-investigators. Sustainable development of urban transport systems with respect to to human exposure to air pollution. Science of the Total Environment submitted (Proceedings of the 7th Highway & Urban Pollution Symposium, Barcelona, May 2002) 5) Stevens E, P Cullinan, R Colvile. Urban air pollution and children’s asthma: what do parents and health professional think? British Medical Journal submitted.