Summary

The project is intended to evaluate the emissions and dispersion of primarily volatile hydrocarbons and PAH in the urban region of Stockholm. It also intended to quantify the main the sources of inhalable particles (PM₁₀ and PM_2.5). Many of these substances have important health impacts (benzene, ethylene, propylene, formaldehyde and PAH) and are important precursors for the formation of tropospheric ozone and other oxidants.

A combination of measurements, dispersion modelling based on present knowledge of emissions from different sources and source-receptor-models will be used to evaluate the contribution of different sources to the distribution of these substances within the Stockholm region.

Aim of the research

The scientific objectives are to

• establish source-receptor relationships for hydrocarbons (alkanes, alkenes, aromatics, oxygenates and PAH) and particulate matter
• assess the relative contribution of individual sources for the distribution of these compounds and to evaluate emission inventories using a combination of measurements source-receptor models and dispersion models

The first measurement campaign has been started — emission measurements in a traffic tunnel in order to obtain detailed source profiles for different vehicle types and different fuels during driving conditions. The aim of the tunnel study is to collect a complete data-set that can be used as source fingerprint for road traffic in Stockholm and to be able to distinguish between gasoline and diesel exhaust. For the latter purpose special attention is focused on certain PAH and higher molecular volatile organic species that has been suggested to be useful (Khalil et al., 1995; Benner et al., 1995; Pierson et al., 1995). Elemental carbon, organic carbon, PM₁₀, PM_2.5 NO_x, CO, number of particles and tunnel ventilation rate are also measured continuously (see Table 1).

For the different source types emphasis will be placed on identifying unique compounds that can be used as tracers in the imission measurements. To distinguish between gasoline and diesel engines PAH and VOC’s have been successfully used in other studies (Khalil et al., 1995; Venkatram and Friedlander, 1994; Benner et al., 1995). Emission data will be based on the existing database, literature reports and other databases (e.g. US EPA emissions database - US EPA, 1990). Most emission factors are based on chassis dynamometer exhaust measurements where a few different vehicles are driven in a specific driving cycle. The driving cycle consists of a mixture of stops, accelerations and driving under constant speed at different speeds. Different driving cycles are used for different types of roads and different vehicles — buses, trucks or automobiles. In addition, different driving cycles are used in Europe and in USA. The emission factor will then be an average value for the driving cycle. In order to be able estimate the emission from road traffic in a part of a city or near high-ways emission factors based on a certain driving cycle may not be very representative. Therefore emission estimates based on real world driving conditions are needed.

The campaign started in November 1998 and will be finished in February 1999. Results will be evaluated using different types of source-receptor models.

Aim for the coming year

A measurement campaign will be conducted in Stockholm during the summer 1999 and winter 1999/2000. These data will be used to evaluate source contributions and compare with results using dispersion models and source specific emission factors. The ambient air measurements should provide a complete data-set that can be used both for receptor modelling and comparison with results from dispersion models.

The ambient and emission data are used as input to receptor models and ambient data are also used to validate meteorological air pollution dispersion models. Data from traffic tunnels may be compared with emission estimates based on dynamometer emission measurements.
 
 

Apart from air pollution data, the dispersion models requires meteorological and physiographic data. All this information is provided from the Air Quality Management system that is in operation in the county of Stockholm since 1994. Meteorological data and data on air pollution concentrations of NOx, NO₂, O₃, SO₂, CO and a number of other trace gases are stored every hour. Air pollutants are routinely measured both outside the urban areas and in the central part of Stockholm, both along heavily polluted streets and at roof level. Three meteorological masts equipped with high quality sensors provide input data for a wind model which in turn provide the input data for the dispersion models.

Two different sites will be studied. Firstly, the central part of Stockholm where road traffic is the main source and secondly a suburban site with substantial contribution from other sources than road traffic. The species analysed and methods that will be used are listed in the table below. The methods have different time resolution — from minutes to one day. Care need to be taken to be able to obtain the same time resolution of the different compounds in order to be able to use the receptor models. The temporal variation will also be evaluated at the two sites.

Table 1 Species measured, methodology and time resolution.
 

Species measured	Method	Time resolution
VOC > C2:  Alkanes, alkenes, aromatics	Steel canister sampling GC/MS-analysis	1 hour
Benzene, toluen, xylenes	BTX (continuous GC)	1 hour
Aldehydes and ketones	DNPH-cartridge HPLC-analysis	1 hour
VOC > C6 (alkanes, alkenes)	Tenax-tube GC/MS-analysis	1 hour
PAH	GC	1 hour – 1 day
Total mass (fine and coarse separate) Elements: Al, Si, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Zr och Pb	Mass of particles (fine and coarse) Impactor (filter) PIXE-analysis	1 hour
Size distribution of the mass of the aerosol (0,003 to 10 µm)	DMPS and APS	Few minutes
NOx, CO, SO2 and O3	Standard instrumentation as  part of the environmental monitoring programme in Stockholm	1 hour
PM10 and PM2.5	TEOM	1 hour
Elemental and organic carbon	ACPM	1 hour

 

References