Assessment of Representativeness of Air Quality Monitoring Stations

1. Assessment of Representativenessof Air Quality Monitoring Stations Geneva, 11.6.2007 Wolfgang Spangl

2. 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 with TNO Central Institute for Meteorology and Geodynamics, Vienna

3. 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

4. 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

5. 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: • A definition of „representativeness“ • Setting quantitative criteria for representativeness • 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.

6. “Representative area” of monitoring stations Be aware that both • Definition and • Quantitative criteria are deliaberate. Other definitions and criteria are possible. Definition and criteria esentially influence the outcome of representativeness assessment.

7. 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: • Emissions • Dispersion conditions due to buildings, topography and climate • Atmospheric transformation and transport

8. 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 mean • Ozone: 90.4-percentile of daily maximum 8-hour mean values (equivalent to 25 days per year above 120 µg/m³)

9. 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

10. 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.

11. Similar reasons for similar concentrations: Emissions Classification according to emissions of • Local road traffic • Domestic heating • Industry 3 classes each • A monitoring site is representative for areas falling into the same class as the respective monitoring site

12. 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)

13. Large-scale Regions with different topography and climate

14. 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

15. 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)

16. 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)