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
Model accuracy is usualy determined by comparing model results with air quality observations;
the basic problems encountered are primarily related to
While monitoring data describe concentrations over time at
a point location based on small volumes (several liter) of air samples,
the model estimates average concentration within a time step (e.g., an hour)
for a comparatively very large volume of air (usually several million liters),
under assumptions of complete mixing within the model grid cell/volume or
as resulting from a (tenous at best) steady state assumption.
- the intrinsic uncertainty of the oberservations themselves and their sample nature;
- the vastly different scales involved when observing and modelling a turbulent process.
For regulatory purposes, the expectations on model accuracy are defined in
Council Directive 1999/30/EC of April 1999 in Annex VIII:
Data Quality Objectives and Compilation of Air Quality Assessment:
The following data quality objectives for the required accuracy of assessment methods ...
are laid down to guide quality-assurance programmes.
||SO2, NO2, NOx
|Hourly averages || 50 - 60 %|| not defined at present
|Daily averages || 50 %|| not defined at present |
|Annual averages || 30 %||50 %
Comparison with monitoring data: model validation
AirWare offers two mechanisms to compare monitoring data and model results
for the grid cells conatining the monitoring station: