1. Summary

An urban emission inventory (SO₂, NO_x, VOC and HM) for the Antwerp area (Fig. 1) has been developed, which includes industrial sources, road transport and space heating. The spatial resolution is determined by a national emission inventory, as provided by the Flemish Environmental Agency (VMM, 1997), containing yearly averaged emission data for point sources, line sources, (motorways and national main roads) and 1 x 1 km² area sources for space heating and urban road transport. The temporal emission variations are modelled using temporal emission factors as based on various sources of emission measurements and national statistics (eg. traffic counts and several years of degree-days measured at different locations).
 

Much attention is paid to road transport emissions. They are derived by a "bottom-up" approach using chassis dynamometer tests and VITO’s on-the-road traffic emission measurements in combination with an urban traffic flow model, which is actually used by the Antwerp City authorities and includes statistics on traffic numbers and vehicle types for a network of almost 2000 road segments. The emission factors are partially derived from the on-the-road traffic emission measurements carried out for gasoline passenger cars with a closed-loop controlled three-way-catalyst (TWC) and for a carburetted non-catalyst car (De Vlieger, 1997). The emission factors for other vehicle types were derived from the joint EMEP/CORINAIR Atmospheric Emission Inventory Guidebook (Mc Innes, 1996), following the COPERT-II methodology.

2. Aim of the research

The urbanised triangle Antwerp-Brussels-Gent is located in Northwest Europe and can be characterised by open, flat terrain conditions. There is a dense Automatic Measurement Network to monitor the air quality. Several meteorological towers are part of the network. The use of satellite remote sensing data for this triangle will complement the data from the existing monitoring stations and will induce geographical consistency in information. For the assessment of the air quality in this triangle, the objectives are:

• The evaluation of heat fluxes of the urban area based on satellite observations
• The estimation of atmospheric stability with satellite remote sensing data
• The development of an emission inventory for specific urban environments
• The development and refinement of existing modelling tools for these urban environments
• The provision of the resulting data sets (emissions, meteorology and immissions) to other groups for model evaluation

A methodology will be developed for the estimation of atmospheric stability based on (satellite) remote sensing and on an operational basis. Satellite derived data and continuous meteorological tower-based measurements (for calibration) are integrated in an operational scheme for the determination of atmospheric stability. The scheme will be demonstrated.

The road transport emissions of the emission inventory will be estimated with VITO’s on-the-road emission and energy measurement system in combination with national statistics on traffic numbers and vehicle types. For industrial sources and space heating a top-down approach based on a harmonised methodology will be followed.

Modelling tools will be refined to analyse source-receptor relationships and temporal variations in urban air quality. The models will also be used to control the quality of the data sets (emissions, meteorology and immissions) that will be made available for model evaluation.

3. Activities during the year

Specification of data on atmospheric stability

Evaluation of surface heat fluxes and specification of atmospheric stability using remote sensing data. Design of the procedures needed to estimate surface heat flux and atmospheric stability using remote sensing data. Implementation of the procedures and testing the method using an existing NOAA data set. Successful implementation of the methodology and testing with ground-truth data.

Development of an emission inventory for specific urban environments.

Acquisition of VOC emissions; spatial and temporal specification of road transport emissions in the urban triangle using VITO’s on-the-road emission and energy measurement system (VOEM) in combination with statistics on traffic numbers and vehicle types. A detailed emission inventory was obtained for the Antwerp area (including temporal and spatial distributions) based on a traffic flow model provided by the City of Antwerp.
 
 
 
 

4. Principle results

The Emission Inventory for the Antwerp area (Fig. 1) can be characterised by the presence of a relatively large contribution of industrial point sources. In 1996, 72 % of the NO_x(NO₂) emissions and 94% of the SO₂ emissions within the urban area of Antwerp could be allocated to industrial point sources. Since 1993, industrial companies are obliged to report their emission yearly. Based on these registrations and on additional calculations and estimates using statistical data and emission factors from the literature, the Flemish Environmental Agency composes a yearly emission inventory.

For the Antwerp area (20 x 20 km²) 208 point sources were registered emitting NO_x(NO₂) and 174 point sources were emitting SO₂ in 1996. Fig. 2 shows the cumulative distribution of the industrial point source emissions, both for NO_x and for SO₂. It can be seen that within the Antwerp area, the largest 15% of the industrial point sources are responsible for 95% of the industrial SO₂ emissions. For the NO_x(NO₂) emissions, 95% of the industrial emissions can be allocated to only 30% of the point sources.
 
 

The total amount of SO₂ emitted in 1996 within the urban area of Antwerp was 53561 tons, which is almost one third of the total SO₂ emissions in Flanders. The largest contribution of the various source categories to the SO₂ emissions is coming from industrial point sources (94%). The total amount of NO_x(NO₂) emitted in 1996 was 26317 tons, which is 15% of the total NO_x(NO₂) emissions in Flanders. With 72% and 24% respectively, the industrial point sources and traffic provide the largest contributions to the NO_x(NO₂) emissions in the Antwerp area.

5. Main conclusions

• Only a small fraction (15-30%) of the industrial point sources is responsible for 95% of the SO₂ and NO_x(NO₂) emissions in the urban area of Antwerp
• Industrial point sources dominate the emission inventory for the Antwerp area. In case of SO₂, 94% of the emissions in 1996 are coming from industrial point sources.

 

 
Specification of data on atmospheric stability

Extension of the methodology to determine surface heat fluxes using satellite remote sensing to a versatile scheme from which atmospheric stability parameters (o.a. Bultynck-Malet) can be derived. Comparisons with data from a meteorological tower (at Mol).

Development of an emission inventory for specific urban environments.

VOC split, detailed modelling of traffic emissions; detailed emission inventories for the Gent and Brussels area. Quality control by comparing the (modelled) inventory results with airborne and ground based measurements.

 
The authors would like to thank the Flemish Environmental Agency (VMM) for their financial support in carrying out the project on urban emission inventories. Furthermore we would like to thank the various departments of the City of Antwerp (Traffic Dept. Environmental. Dept.) for their fruitful co-operation.