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Assessment of Representativenessof Air Quality Monitoring Stations

Geneva, 11.6.2007

Wolfgang Spangl

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Service contract to the Commission for the Development of the methodologies to

determine representativeness and classification of air quality monitoring

stations

Contractor to DG ENV: Umweltbundesamt Austria

Subcontracts withTNOCentral Institute for Meteorology and Geodynamics, Vienna

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Motivation for Assessment of Representativeness

Information about air quality is required for the whole territory (e.g. in the AQ framework Directive 96/62/EC)

But: Monitoring gives information for distinct point locations (i.e. monitoring stations)

Methods to get spatial information about air quality are required

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Spatial Information - Modelling

Spatial information about air quality can be achieved by modelling. However, models have some disadvantages:

Expensive High demand on input data (emission,

meteorology, land use, …..) Limited resolution (regional, urban, street, …) Limited representation of „reality“ due to

various uncertainties

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Spatial Information – Representativeness of monitoring data

Spatial information about air quality can be achieved by extending measured data to the “representative area” of a monitoring station.

To delimitate the representative area requires:1. A definition of „representativeness“2. Setting quantitative criteria for representativeness3. The identification of the area which fulfills the criteria

for representativeness, based e.g. on a combination of model results, emissions, land use data, etc.

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“Representative area” of monitoring stations

Be aware that both Definition and Quantitative criteriaare deliaberate.

Other definitions and criteria are possible.

Definition and criteria esentially influence the outcome of representativeness assessment.

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Definition of Representativeness

The area of representativeness is defined by the criteria:1. The concentration within a certain range. The concentration is assessed according to limit and target values of EC legislation, related to annual means or annual exceedance numbers.2. Similar concentrations shall be determined by similar reasons:EmissionsDispersion conditions due to buildings, topography and climateAtmospheric transformation and transport

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Definition of Representativeness

Statistic parameters related to EC AQ regulations to determine representativeness:PM10: Annual mean, 93.2-percentile of daily mean values (equivalent to 35 days per year above 50 µg/m³)NO2: Annual meanOzone: 90.4-percentile of daily maximum 8-hour mean values (equivalent to 25 days per year above 120 µg/m³)

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Definition of Representativeness

The concentration in the area of representativeness of a certain AQ MS shall be within a range of 10% of the total concentration range observed in Europe.

PM10: Annual mean: ±5 µg/m³, 93.2-percentile of daily mean values: ±8 µg/m³

NO2: Annual mean: ±5 µg/m³, which shall also be applied to NOx

Ozone: 90.4-percentile of daily maximum 8-hour mean values: ±9 µg/m³

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Definition of Representativeness

The spatial variation of parimary pollutants (incl. NO2) is higher than for partly secondary pollutants (PM10) and secondary pollutants (Ozone).

Therefore the representative areas, applying these criteria, are, on general, smaller for NO2 and larger for Ozone.

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Similar reasons for similar concentrations: Emissions

Classification according to emissions of Local road traffic Domestic heating Industry3 classes each A monitoring site is representative for areas

falling into the same class as the respective monitoring site

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Similar reasons for similar concentrations: Dispersion and atmospheric transport

Local dispersion due to building structure and street geometry: street canyon; detached buildings; flat terrain; exposed

Regional dispersion due to topography (10km): Flat terrain; hilly terrain; valley; basin; ……

Large-scale (100km) Regions with different topography and climate: Alps (north/south), Po-Valley, Pre-Alpine Lowlands, Pannonian Plane, ….

Maximum extension of representative area related to chemical (trans)formation of NO2, O3, PM10, … (depending on average wind speed, radius approx 100 km in Central Europe)

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Large-scale Regions with different topography and climate

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Methods to determine the area of Representativeness

Sources of spatial information: Modelling Measurement (regular monitoring networks,

temporal measurements) Surrogate information: emission inventories;

surrogate for emission: land use (e.g. CORINE landcover), TeleAtlas roads), population distribution

Model results and (additional) measurement data are used to derive relations between surrogate information and concentrations

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Area of Representativeness – based on model results and land use data

Klagenfurt (Austria), NO2

Representative area of two monitoring stations: urban background, annual mean 27 µg/m³ (yellow)kerb side, annual mean 43 µg/m³ (red)

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Area of Representativeness – based on surrogate information

Illmitz (rural background), Ozone

The area of representativeness is part of the Pannonian Plane (dark green) and excludes:Area above 300m (brown)Large cities (blue)Major roads (red)