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 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

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

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

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

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

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

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

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)

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

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