1. Ian D. Longley, M.W. Gallagher
Particle and sensible heat fluxes measured by eddy covariance above and within an urban canopy
Ian D. Longley, M.W. Gallagher
School of Earth, Atmospheric & Environmental Sciences,
University of Manchester, UK
Presented at the 6th International Conference on the Urban Climate, Göteborg, 2006

2. Particulate emissions from cities
Biosphere impacts
Climate impacts
Regular emission cycles
Sheltering, recirculation, deposition, inversions
Within urban canopy:
Direct impacts on human health
Advected air is relatively clean
Emission from surface following relatively predictable cycles
Net emission from city has downwind impacts – direct radiative, CCN and hence indirect radiative, biosphere impacts on deposition
Physiochemical nature depends upon physiochemical nature of emissions & timescales
Recirculation and trapping in UCL

3. PM10 emission inventory (UK NAEI) tonnes km-2 a-1
Above: all sources
Below: road transport (48% of total)
No information on composition or size distribution
No temporal information
No experimental verification
Current emissions quantified on 1km x 1km grid estimates of PM10 (mass of particles below 10 microns).
Values reported are tonnes / km2 / year. No information given on temporal variation.

4. Ultrafine particles
Above: mass size distribution from Princess Street, Manchester
UFP toxico link
Coarse increasingly important as UFP tackled, and in terms of mass, health effects not insignificant
Above: number size distribution from Princess Street, Manchester

5. CityFlux University of Manchester Centre for Ecology & Hydrology (UK)
2004-7
Pilot study: Manchester June - July 2005
Direct measurement of particle fluxes from city centre by eddy covariance

6. Manchester, UK 50 km inland 2.5 m population High density core
zH ~ 20 m
50 % PM10 from road transport
Trips into centre: ~ 50 % car,
50% public transport
Very little vegetation in core

7. CityFlux – Manchester (UK) – July 2005
Canopy/Canyon sites:
Tower site: Portland Tower (90 m)
1. UoM
2. Deansgate

8. CPC (Eddy Covariance) Flux system
u,v,w
Dorsey et al., 2002, Atmos. Environ. 36,
N (Dp > 17 nm) cm-3
40 lpm

9. Total particle number and sensible heat flux
Mean particle flux: cm-2 s-1 or cm-2 s-1 (upward only)
cm-2 s-1 (upward only) Stockholm (Mårtensson et al., 2005)
Deposition rare
Approximately log-normal distribution of 10-minute average particle fluxes

10. Mean diurnal fluxes See also poster by Martin et al.
Above: Mean diurnal fluxes at 90 m
Above: diurnal mean traffic volume in subject street canyon
Above: Diurnal mean concentrations at 2 and 25 m
Mean sensible heat flux = 106 W m-2
Some hint that ventilation velocity is positively related to u* and is enhanced in unstable conditions
Sunrise 05:00, Noon 13:15, Sunset 21:20 local
See also poster by Martin et al.

11. Canyon roof level (Maybrook House, Deansgate)
Highly complex flow with large and variable degree of sheltering

12. Conclusions
Particle number fluxes were measured at 90 m above central Manchester
Fluxes had a clear diurnal cycle, with peak in early afternoon - very similar to that for sensible heat flux
These results very similar to Edinburgh 2001
Sensible heat fluxes at canyon roof level very similar to 90 m, although decay in afternoon was more gradual

13. Forthcoming analysis Spring/Summer 2006
Winter 2006 data (poster by Martin et al.)
Influence of stability
Model for particle ventilation fluxes
Prediction of urban canopy concentrations
Spring/Summer 2006
Continued measurements at Portland Tower, including size-segregated fluxes
Multi-level compositional measurements by AMS
Tracer release to identify source-receptor relationships and transport timescales

14. And GVA Grimley for kind permission to use Maybrook House
Acknowledgements
Many thanks to Bruntwood Properties for kind permission to use Portland Tower
And GVA Grimley for kind permission to use Maybrook House

15. Mean number flux as function of wind direction
40 000
20 000

16. PM10 emission inventory (NAEI)
Above: all sources
Below: road transport (48% of total)
PM10 inventory gives no clear clues as to enhanced sources in WNW

17. Local WNW sources?
Portland Street
Princess Street
Construction sites

18. Chinese cooking?
But low fluxes on Sundays

19. Mean diurnal particle fluxes (evening peak)
Sunset at ~ 21:20 local time
WNW is prevailing wind direction in June & July
Peak in diurnal cycle in evening associated with WNW winds.
Check every day – did evening peak occur?
Frequency of WNW winds peaked in late evening
Second evening peak always and only seen in WNW winds Mon-Sat

20. Street canyon particle concentrations and composition
Above: time series of particle composition mass loadings from Aerosol Mass Spectrometer (AMS)
Above: diurnal mean traffic volume in subject street canyon
25 m level will more closely resemble ‘urban background’, i.e. workplace (and some residential) exposure
Above: diurnal mean particle number concentrations (DMPS) at top and bottom of street canyon
Above: Diurnal mean of particle composition mass loadings from AMS

21. Urban Particle Numbers
Particle number concentrations dominated by ultrafines
Above: mass size distribution from Manchester street canyon
Above: number size distribution from Manchester street canyon
Longley et al., Atmos. Environ.
Particle toxicity appears to lie in ultrafine fraction
Traffic is the dominant urban source, but emission factors poorly quantified