AirWare   On-line Reference Manual

  Release Level 5.4
  Release Date 2008 10
  Revision Level 1.0
Last modified on:   Monday, 20-Jul-09 14:03 CEST

Single Source Impact Assessment

AirWare provides an option to perform a screening level impact assessment for any existing, hypothetical new, or modified point, area or line emission source. This is based on annual runs of the AERMOD model with an hourly resolution.

Depending on data availability, the assessment results can include:

  1. Average and maximum concentrations (annual average of hourly values) in a user defined domain around the source and any number of user defined target areas (receptor areas);
  2. Area above a user defined reference concentration;
  3. Population exposed to an annual average concentration above a user defined level (require spatially distributed population data;
  4. Land use class specific impacts or damage function evaluation;
  5. Number of violations of hourly standards at a number of automatically determined or user define receptor areas and/or building points
  6. Relative contribution of the source expressed as a percentage contribution, in the area (sum of model grid cells) where the source contribution exceeds a user define absolute value. This however, requires a reasonably complete regional emission inventory to establish a baseline or background concentration.

Parameter settings

The impact assessment works on the basis of the standard emission inventory, and is implemented for point and area sources, e.g., representing fugitive or distributed emissions.

Source selection:   the first user choice is the selection of an emission source, or the definition of a new one. The source to be evaluated is selected from the coresponding OBJECT data base (by source type) or the emission inventories (by geographical domain). Links are part of the impact assessment start and main scenario page. If a new source is being defined for the purpose of the assessment, tagging it as hypothetical or planned, will exclude it from consideration from the normal scheduled daily and hourly model runs.

Contact: Every impacts scenario includes a Contact institutional reference and contact person that can be used to capture (optional) administrative data describing the owner/operator of the emission source to be evaluated.

Pollutant:   the user can select a (conservative or first order decaying) pollutant, the emission strength and temporal emission patterns are automatically copied from the emission inventory.

For PM10, the assessment will be performed in terms of daily (24 hour) averages.

Thresholds and standards: the impact assessment is done in reference to threshold or standard values for ambient concenatrtion the user can specify for

  • short-term (hourly values, and daily average for PM10)
  • long-term (annual average and maxima).

Model domain:   around the source selected, a default domain of 10 by 10 km is being constructed. The user can modify (extend) the size of this domain up to 30 by 30 km, depending on the nature (emission strength and height) of the source.
Please note that the model performance is linear with respect to the grid cells defined, i.e., the square of the domain linear dimension.

    Domain definition: The model domain for the impacts assessment can be set by the user, or determined automatically by a pre-processing step that will guarantee that the domain is big enough to include all values above the user defined short-term threshold value plus some reasonable margin, and as small as possible for efficient computations.
Meteorological scenario:   the next choice is the meteorological scenario, in which the user can select one or more monitoring stations and a year for the analysis. A check function can be used to verify that the data set selected is sufficiently complete for the intended annual model run.

Run request:   with the scenario defined, the user can submit a run request. If the (meteorological) data are complete and all necessary scenario parameters have been defined completely and consistently, the model will be run for 24*365 hours. Depending on settings, this may take several hours.

The run request will be confirmed in a separate dialog box, where an eMail address for notification when the run is completed can be specified.

Receptor Locations

The impacts are calculated for
  • the entire domain, and the area where the absolute contributions from the source evaluated exceeds user defined thresholds;
  • a set of user define receptor points (building points)
  • a set of user defined receptor area
  • and OPTIONAL set of automatically determined receptor points. Their location can be calculated in a pre-processor step that finds a set of points of maximum annual average and a minimum distance from each other
    (see also: Locating Monitoring Stations.)

Assessment results

The primary assessment result is a matrix of average annual concentrations around the source, shown as a color coded transparent map overlay. The parallel statistical information includes:
  • annual average and hourly maximum concentration in the model domain;
  • annual average and hourly maximum concentrations in all receptor areas;
  • areal extent where a (user defined) reference concentration (annual average) is exceeded;
  • for all building points (receptor points) in the area, average, maximum concentration and the number of hourly violations of a user defined reference value.
  • population exposure, longterm (number of people living in an area where a user defined standard is exceeded).
The assessment can be embedded into a rule-based screening level EIA framework that provides a checklist of issues and criteria that are evaluated by classifying and interpreting the model results with a set of first-order production rules.

Relative contribution

As an option, the source contribution (annual average) can be calculated as a relative contribution over the background or baseline immissions due to all other local sources. This will run the model twice, once for all sources in a larger domain whithin which the domain user for the assessment is nested, and once for the new source, to determine its relative contribution.

The reference for this calculation of relative contribution is the area where the primary absolute contribution from the primary source exceeds a user define absolute reference or threshold value.

For the background calculation, the user can defined an alternative (larger) domain, or use the model itself to determine an appropriate background. This is achieved by finding the domain size, where any increase in the domain (and thus additional emission sources) will no longer increase the average concentration in the impact area due to the increasing distance of these additional sources. However, please note that the latter computations can take several (many !) hours due to their iterative nature.

Source control

For conservative pollutants and annual average values, a simple inverse problem solving mechanism to determine the maximum allowable emissions to not exceed a user defined standard at a given set of locations (entire domain, receptor areas, building points, user defined or automatically located) is also available.

Complex optimization

For a given source, the user can specify several emission control strategies (they can be mutually exclusive or freely combined) with their associated emission reduction efficiencies and cost functions (annualized investment, operating costs), as well as technical measure such as different stack height with their associated costs. The model find the minimum cost configuration to meet a set of user defined constraints. From the set of feasible solutions, an optimal solution can be found using a discrete multi-criteria optimization tool.

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