Dispersion 2.1

"A dispersion model for industrial releases to air and urban releases"

Dispersion is a user-friendly PC tool intended for planning and estimating air quality in an urban environment or in the vicinity of industrial plants. The model is used in environmental impact studies or in scenario studies to quantify the effect on air quality from existing emissions or planned actions. The model calculates mass concentrations and fluctuations of classical air pollutants and population exposure thereof. The results are analysed and presented as digital thematic maps in a GIS system or in tables or as time series.

Complies to EC Directive 96/62/EC

Dispersion 2.1 may be used to estimate air quality in a zone, if the concentrations of a pollutant are below the upper assessment threshold, which usually is 60-70% of the limit value. With Dispersion, you can design an emission scenario that is applied in real meteorological situations during long or short periods, which are evaluated in accordance with the framework directive and its daughter directives. Single cases may be studied to find explanations for an episode.

Environmental Impact Assessment Studies

In EIA studies, present situation and future alternatives may be studied regarding air quality and population exposure. Dispersion 2.1 includes a tool to study co-variation between calculated concentrations and population data.

How large impact will planned actions have on air quality? With Dispersion, you may quantify the impact from changed stack height, emission reduction measures or changed driving conditions.

With Dispersion, you may study emissions from point sources, area or line sources. Each source type has its own dispersion algorithm, mainly depending on release height, wind direction and distance from the source. Emission data and the time variation and dependence of meteoro-logical parameters are specified. Emissions may be continuous or intermittent. Also fugitive emissions may be entered.

Emission factors for nitrogen oxides, carbon oxide and particulate matter are stored for Swedish vehicle parks. The dispersion model may also be used for other species like sulphur dioxide or passive species with or without buoyancy effects. Building downwash effects are included.

The concentration in street canyons may be calculated. The street canyon model includes a photochemical reaction for nitrogen dioxide, formed by reaction with ozone.

Source data is stored in a source register, but it may also be imported/exported into a source database in MS Access 97.

The system normally uses meteorological data from an automatic weather station, completed with cloud data and ground parameters from a synoptic weather station. In order to describe conditions up to the inversion layer, aerological soundings made by SMHI and other institutes are used.

It is also possible to adapt the system to local measurements of temperature, wind, solar radiation and vertical temperature gradient in a mast arrangement.

There have been applications where weather forecasts were used as input to Dispersion to generate air pollution forecasts.

In EIA studies, present situation and future alternatives may be studied regarding air quality and population exposure. Dispersion 2.1 includes a tool to study co-variation between calculated concentrations and population data.

How large impact will planned actions have on air quality? With Dispersion, you may quantify the impact from changed stack height, emission reduction measures or changed driving conditions.

MapInfo Professional is used to enter sources and to present the results. The results may be presented as isolines or coloured transparent areas with concentrations above certain levels upon a city map or aerial photograph. The maps may be entered into Word documents for further reporting.

During the two years that have passed since the release of previous version, Dispersion has undergone a number of improvements:

• The installation is CD-based.
• New documentation has been written
• The on-line help system gives position-dependent information.
• Error status messages are more precise.
• The system is year 2000 certified.
• Statistical output complies to new Swedish air quality standards.
• Emission factors for traffic have been updated until year 2005.
• Calculation speed has improved by a factor 30 on average, using the same processor and clock frequency.

System requirements

• Operative system: Windows 95/98 or Windows NT 4.0
• Processor: Pentium 233 MHz or higher, alternatively AMD K6 or Athlon
• RAM: min 32 MB
• MS Access 95/97 is required if you want to import/export source data.

For further information, please contact:

Lennart Larsson or Hans Backström
SMHI Environment Services
SE-601 76 NORRKÖPING

Phone: +46 11 495 80 00

Email: environment@smhi.se

Uppdated 2002-10-14