Presentation on theme: "Attack of the Toxic Mist – Ian D. Longley School of Earth, Atmospheric & Environmental Sciences, University of Manchester Why we study Urban Aerosol Dispersion."— Presentation transcript:
Attack of the Toxic Mist – Ian D. Longley School of Earth, Atmospheric & Environmental Sciences, University of Manchester Why we study Urban Aerosol Dispersion
Urban air is cleaner than it was – isn’t it?
Urban smogs in the UK: December 1991 March 1996 December 2001 February 2003 Aftermath of the Clean Air Acts
PM 10 Mass concentration of particulate matter with an aerodynamic diameter < 10 m >50% probability of penetrating into thorax UK-wide Automated Urban and Rural Networks Bury (M60)Piccadilly GardensNorth-West
What PM 10 levels do we experience? Means: Piccadilly 27 Eccles 23 Stockport 22
PM 10 episodes and health risk Rise of 10 gm -3 PM 10 linked to ~0.5% rise in mortality Translates as ~8 000 deaths brought forward per year in UK urban population (COMEAP, 1998) – compared to total deaths due to RTAs. PM 10 also linked to increased morbidity No lower threshold! Deaths from respiratory causes Also cardiovascular causes Deaths mostly of the ‘vulnerable’ Episode promotes an exacerbation of pre-existing condition What is the cause?
Urban particle sources and sizes Vehicle emissions, combustion Long-range transport, secondary particles Dust, wear products, biological particles, minerals Measured in Princess Street, Manchester PM 10
Urban Particle Size Distributions Particle number concentrations dominated by ultrafines Above: mass size distribution from Manchester street canyon Above: number size distribution from Manchester street canyon Data: Longley et al., Atmos. Environ., 2003.
dM/dlogDa / g m -3 Aerodynamic Diameter (nm) Urban particle speciated mass size distributions UFP mostly organic compounds Also: Black carbon Sulphuric acid i.e. Traffic is the major source Data: Allan et al., JGR 2002, Alfarra et al., Atmos. Environ., 2004
Ultrafine Particles in the body Ultrafines (UFP) efficiently deposit to alveolar walls Overload can cause chronic inflammation and irreversible damage to tissues and defences Inflammatory response triggers systemic reaction in cardiovascular system – increases in blood viscosity, formation and disruption of plaques, heart rate variability. Can lead to arrythmia, ischaemia and heart attack (immediately or in future) Effects seen in ‘non-toxic’ particles – is toxicity in size, surface area or composition???
UFP dispersion in urban areas coagulation condensation Recirculation/sheltering dilution
Ventilation of the urban canopy Regular emission cycles Sheltering, recirculation, deposition, inversions Mean diurnal fluxes at 90 m above Manchester Diurnal mean concentrations at 2 and 25 m NOTE: ventilation is suppressed during morning emission peak Data: NERC CityFlux project, Longley et al., 2006
Long-term PM 10 exposure and health risk For long-term exposure relative risk is doubled to ~1.0% (Dockery et al., 1993, Pope et al., 1995, Kunzli et al., 2001) Suggests long-term exposure (to mean or repeated episodes?) causes or increases vulnerability Episodes NOT followed by ‘harvesting’ for cardiovascular deaths – episodes create a newly vulnerable cohort Consequences: Need to consider complete history of personal exposure, especially UFP
Fixed PM 10 monitors versus personal UFP exposure PM 10 monitors are supposed to be ‘representative’ UFP has high spatial gradients, fixed monitors expensive and unrepresentative(?) Daily/Hourly PM 10 data biases concept of episode to day/hour durations Personal UFP exposure dominated by short (< 1 hour) very high ‘excursions’ Need to consider residential and workplace, but especially commuting exposures Walk to stop At bus stop On bus
Street canyon UFP number size distribution in channelled flow
Street canyon UFP number size distribution in recirculating flow Recirculation caused by perpendicular approach flow (>40 deg from canyon axis) Extra particles in ‘fresh exhaust’ size range Data: Longley et al., Atmos. Environ., 2003, CityFlux: Longley et al., 2006
Parameterising street canyon turbulence i 2 = (A i U) 2 + 2 2 Where i = u, v, w A i, 2 = f(z) Longley et al. 2004, Atmos. Env. 38, Longley et al. 2004, Atmos. Env. 38, Explicit numerical modelling of dispersion hampered by sub-grid scale processes Thus, empirical modelling presents practical alternative
Outstanding problems Rate of dispersal from street canyons – advection - turbulent diffusion – deposition Generalising dispersion into the neighbourhood Coagulation/condensation/nucleation/reactions – require timescales How indoor exposure is related to outdoor concentrations Rapid growth of megcities – a challenge for the 21 st century
Thanks for your attention
Statistical variation in ultra-fine concentrations
Spatial variation in urban PM 10 PM 10 heavily influenced by Resuspended dusts Long-range transport of secondary PM … but does this represent the variation in exposure potential? Emission/dispersion modelling leads to…
Edinburgh measurements (SASUA, )
SASUA diurnal particle number flux (May) Below: sensible surface heat flux Dorsey et al., 2002, Atmos. Environ. 36, Diurnal cycle in urban ventilation related to heat flux cycle
UFP dispersion in road corridors Factors affecting dispersion Ptrak data Visualisation of road corridor concept