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

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 °
Concentrations typical for cities
UFP: cm-3
AP: cm-3
Coarse: 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

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