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Results from the SMEAR III urban measurement station

Results from the SMEAR III urban measurement station. Leena Järvi et al. URPO – Urban and Rural Air Pollution seminar 22.11.2007. Introduction. The SMEAR III measurement station started in Helsinki in autumn 2004

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Results from the SMEAR III urban measurement station

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  1. Results from the SMEAR III urban measurement station Leena Järvi et al. URPO – Urban and Rural Air Pollution seminar 22.11.2007

  2. Introduction • The SMEAR III measurement station started in Helsinki in autumn 2004 • To get information about the sources and dispersion of air pollutants, turbulence and air chemistry • Continuous measurements in • aerosol particle dynamics • atmospheric chemistry • micrometeorology • weather monitoring • ecophysiology of trees

  3. Turbulent exchange (momentum, heat and CO2 fluxes) and meteorological parameters are measured in a 31 m high tower • Aerosol particle and • trace gas instrumentation • are located in a container • next to the tower • Surrounding area can be • divided into three land use • sectors: urban, road and • vegetation

  4. Methods • Aerosol particle measurements are carried out with twin DMPS (Differential mobility particle sizer) and APS (Aerodynamic particle sizer) • Aerosol particle data is divided into three classes which have different dynamics and sources • In urban areas, ultrafine particles (UFP, d<0.1 μm) are mainly produced in combustion processes • Accumulation particles (AP, 0.1< d < 1 μm) are also combustion related and the size of the is favorable for LRT • Coarse particles (>1 μm) are mainly resuspended from the soil of roads • Data between May 2005 and June 2007 has been analyzed

  5. Measurements and calculation of turbulent fluxes • Flux is the transfer of some substance/area/time • Turbulent fluxes can be calculated with eddy covariance (EC) technique • Flux is the covariance of vertical wind speed and scalar in question • Setup includes Metek ultrasonic anemometer and LiCor infrared gas analyzer (10 Hz) • Data from Dec 2005 to Jun 2007 was analyzed

  6. Wind direction dependence of aerosol particles • UFP’s and AP’s have dependence on land use cover • Highest coarse particle concentrations are measured in 180-250° • Concentrations typical for cities • UFP: 3000-18000 cm-3 • AP: 500-3300 cm-3 • Coarse: 0.3-1.7 cm-3

  7. Diurnal behavior of aerosol particles for different seasons and separately for weekdays and weekends • The influence of traffic clear in UFP and AP concentrations • Winter UFP values highest • Low mixing heights • Combustion sources Weekdays Weekends

  8. Diurnal pattern of CO2 fluxes in different seasons and land use sectors • Most of the time, surrounding area acted as a source • In spring and summer days, vegetation uptake exceeded the effect of anthropogenic sources in vegetation sector

  9. Correlation between traffic rates and CO2-fluxes • Traffic data available for Jan-Aug 2006 • CO2 flux and traffic rates were positively correlated • Similar results from Edinburgh (Nemitz et al. 2002) Vesala et al. (2007)

  10. Diurnal cycle of sensible heat (black) and latent heat (red) fluxes • Sensible heat fluxes are elevated in urban sector (heat island effect) • Latent heat fluxes are raised by the vegetation cover

  11. Conclusions • Heterogeneous measurement site enables the studying the effect of different land use covers to air pollutants and turbulent fluxes • Ultrafine and accumulation particle concentrations were typical for urban areas and were affected by the road next to the measurement site • The heat island effect was distinguishable in sensible heat fluxes • Surroundings of the site acted as a source for CO2 most of the time

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