Ian Longley Physics Department, UMIST, Manchester, U.K. Fine scale temporal variation in ultrafine particle concentrations in a busy street canyon with consequences for human exposure

PM10 and ultrafine particles (UFP) PM10 linked by epidemiology to poor health Plausible toxicological mechanisms for UFP PM10 influenced by advection and resuspension – small spatial variation in urban areas

Excursions and street canyon exposure Experiments on rats show greater effect if dose delivered in short bursts (Michaels & Kleinman, 2000) Personal exposure of typical person uneven over the day – excursions associated with commuting. Hot spot/background ratio much higher for UFP than PM 10 High, sudden UFP exposures could trigger exacerbations and cardiovascular events

SCAR – Princess Street, Manchester One-way traffic Up to 1100 h -1 Including buses

SMPS (TSI nano DMA) 20 Hz sonic anemometers 2 weeks of measurements, 24 hours a day, Mon-Fri SCAR measurements

Longley et al., 2003, Atmos. Env. 37, SCAR-4 Mean street-level aerosol mass size distribution

SCAR-4 Mean street-level aerosol number size distribution

N 0.1 Ultrafine particle concentration

Parallel flow

Perpendicular flow Wind speed above and within canyon unrelated

Ultrafine N 0.1 (D p <0.1m) concentrations Parallel flow with channelling 10-minute means

Perpendicular flow with channelling

Perpendicular flow with recirculation

Ultrafines number size distribution and in-canyon meteorology

Estimating background N 0.1 from NO x SCAR site Network monitor

Effect of sheltering on concentration enhancement

Statistical variation in ultra-fine concentrations

Comparison with background N 0.1 N 0.1 / cm -3 Street canyonBackgroundRatio mean Rush-hour mean th percentile (1 hr)

Influence of average daily exposure 23 hours background of cm -3 1 hour (peak traffic period) canyon exposure at cm -3 Assume no other significant residential or occupational exposures Background: 80 % Canyon: 20 % average breathing rates are 2 – 3 times higher in canyon, deposition deeper Exposure ratio canyon:background may be 10 –20

 Concentrations of UFP in canyon typically 4.5 times higher than in urban background.  Concentrations dependent upon wind direction.  Perpendicular flow can lead to recirculation. Concentrations on lee side of canyon in the range of – cm -3, i.e. an order of magnitude greater than the background.  Concentrations inversely related to wind speed in the canyon, BUT recirculation also breaks link between wind speed in canyon and aloft.  A person exposed to background for 23 hours and street canyon for 1 (peak) hour receives 20% of exposure in 4% of time.  Brief but very high exposure to ultrafines - high risk to vulnerable individuals, not captured in current regulation of PM 10. Conclusions

With thanks to Martin Gallagher, Mike Flynn, James Dorsey, Paul Williams, Rami Alfarra, James Allan, Mike Cubison, Keith Bower, Karl Beswick, Gordon McFiggans, Tom Choularton (UMIST) plus CERC Ltd., Cambridge, UK Acknowledgements