Input, in the form of emissions and dispersion conditions, is necessary at a similar

spatial and temporal basis as the output concentrations to be calculated by the model.

Data on emissions is required with sufficient spatial and temporal resolution to

describe the important gradients occurring in a zone.

Emission inventories are part of the modelling activity. Methodology for making

inventories have been developed within the EU CORINE work, EUROTRAC

GENEMIS and UNECE EMEP. The harmonisation and standardisation of models

within DGXI, DGXII, European Environment Agency - Topic Centre for Air Quality,

at a number of international organisations and on national scale is progressing. A

compilation is made in Annex VII. The Guidance Report (van Aalst et al. 1997) will

provide valuable information and guidance on which models to use and how to apply


In the assessment of models, monitoring data serve as validation. The validity of the

modelling results depends on the accuracy of the input data as well as on model


Minimum levels of time coverage and data capture, at the necessary levels of

precision, must be established in order to comply with the monitoring objectives.

Based on the results of the NO2 Quality Assurance Programme, organised by the JRC

from 1992 to 1995, the precision and accuracy (expressed as maximum uncertainty)

can be estimated as approx. ±25%. This figure takes into account various

uncertainties, including sampling losses (5%), calibration errors - primary calibration,

transfer standard, routine calibration under field conditions - (±15%), analytical errors

- such as noise, non-linearity, effect of atmospheric pressure and temperature- (5%)

and the effect of interfering gases - water vapour, other nitrogen species - (±10%).


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