Calculation methods | - Urban population exposure:
- Information on cities is obtained from the Urban Audit (UA) data (Eurostat, 2014c). The urban population considered is the total number of people represented by any of the urban monitoring stations in the 'core city' and, from 2016, the 'greater city' of the UA cities taking part in the calculations. Initially, stations in the EEA air-quality database are spatially joined with UA core and, from 2016, greater cities in a geographical information system in order to select those stations that fall within the boundaries of the cities included in the UA collection. The selected stations include station types classified as 'urban traffic', 'suburban traffic', 'urban background' and 'suburban background'.
- According to a study for the European Commission by Entec UK Limited (EC, 2006), in Europe, on average, 5% of the city population lives closer than 100 m from major routes and is therefore potentially exposed to concentrations measured at traffic stations. The remaining 95% of the city population is assumed to be exposed to urban and suburban background concentrations. These percentages vary among jurisdictions.
- To calculate the percentages of persons living closer than 100 m to major traffic routes, national data on the population living closer than 100 m from major roads can been taken from Appendix D (EC, 2006).
- For PM10, PM2.5, O3, NO2 and SO2, only stations with at least 75% of valid data per calendar year are used. For BaP, the minimum data time coverage accepted is 14% (51 days), according to the data quality objectives related to indicative measurements in the Directive 2004/107/EU (EU, 2004).
- For each year, each city
 in country (j), and every pollutant, the total number of urban or suburban traffic stations (nit) and the total number of urban or suburban background stations (nib) are obtained. A percentage (Ptj %) of the total population of the city (Popi) is proportionally assigned to each of the traffic stations and Pbj % of Popi is proportionally assigned to each of the background stations. Thus, every traffic station has an allocated population equal to ((Ptj / 100) * Popi / nit) and every background station has an allocated population equal to ((Pbj /100) *Popi / nib).
EU LIMIT AND TARGET VALUES - Fine particulate matter (PM2.5): The annual mean concentration is calculated for each of the selected stations fulfilling the valid data criteria. Depending on the mean concentration, each station (and its allocated population) is then classified uniquely in one of the two concentration classes (less than or equal to the target value (25 µg/m3), or greater than the target value). The percentage of the urban population allocated to these two concentration classes is calculated by dividing the population represented by the stations assigned to each concentration class by the sum of the population assigned to each station.
- Coarse particulate matter (PM10): For each selected station that fulfils the valid data criteria, the 90.4 percentile (P90.4) of the daily mean concentration series is calculated. P90.4 represents, in a complete series of 365 elements, the 36th highest value. When P90.4 is less than or equal to 50 µg/m3, it indicates that the daily limit value (DLV) was not exceeded on more than 35 days. Depending on the value of P90.4, each station (and its allocated population) is then classified uniquely in one of the two concentration classes (P90.4 > 50 µg/m3, i.e., greater than the DLV and P90.4 ≤ 50 µg/m3, i.e., less than the DLV). The percentage of the urban population allocated to these two concentration classes is calculated by dividing the population represented by the stations assigned to each individual concentration class by the sum of the population assigned to each station.
- Ozone (O3): For each selected station fulfilling the valid data criteria, the 93.2 percentile (P93.2) of the daily maximum 8-hourly mean concentration series is calculated. P93.2 represents, in a complete series of 365 elements, the 26th highest value. When P93.2 is less than or equal to 120 µg/m3, it indicates that the long term objective was not exceeded on more than 25 days. Depending on the value of P93.2, each station (and its allocated population) is then classified uniquely in one of the two concentration classes (P93.2 >120 µg/m3, i.e., exceedance of the long term objective on more than 25 days, and P93.2 ≤120 µg/m3, i.e., exceedance of the long term objective on fewer than or equal to 25 days). The percentage of the urban population allocated to these two concentration classes is calculated by dividing the population represented by the stations assigned to each individual concentration class by the sum of the population assigned to each station.
- Nitrogen dioxide (NO2): The annual mean concentration is calculated for each of the selected stations that fulfills the valid data criteria. Depending on the annual mean concentration, each station (and its allocated population) is then classified uniquely in one of the two concentration classes (less than or equal to the limit value (40 µg/m3), or greater than the limit value). The percentage of the urban population allocated to these two concentration classes is calculated by dividing the population represented by the stations assigned to each concentration class by the sum of the population assigned to each station.
- Benzo[a]pyrene (BaP): The annual mean concentration is calculated for each of the selected stations fulfilling the valid data criteria. Depending on the mean concentration, each station (and its allocated population) is then classified uniquely in one of the two concentration classes (less than or equal to the target value (1.0 ng/m3), or greater than the target value). The percentage of the urban population allocated to these two concentration classes is calculated by dividing the population represented by the stations assigned to each concentration class by the sum of the population assigned to each station.
- Sulfur dioxide (SO2): For each selected station that fulfills the valid data criteria, the 99.2 percentile (P99.2) of the daily mean concentration series is calculated. P99.2 represents, in a complete series of 365 elements, the 4th highest value. When P99.2 is less than or equal to 125 µg/m3, it indicates that the daily limit value would was not exceeded on more than three days. Depending on the value of P99.2, each station (and its allocated population) is then classified uniquely in one of these two concentration classes (P99.2 >125 µg/m3, i.e., greater than the daily limit value and P99.2 ≤125 µg/m3, i.e., less than the daily limit value). The percentage of the urban population allocated to these two concentration classes is calculated by dividing the population represented by the stations assigned to each individual concentration class by the sum of the population assigned to each station.
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Links and references | - Exceedance of air quality standards in urban areas EEA (2019). https://www.eea.europa.eu/data-and-maps/indicators/exceedance-of-air quality-limit-3/assessment-5 Permalink: https://www.eea.europa.eu/ds_resolveuid/13c96efc7a1f44ee9337b2e2cdf0 77a9
- EC, 2006 - Development of a methodology to assess the population exposed to high levels of noise and air pollution close to major transport infrastructure, prepared by Entec UK Limited (Appendix D).
- ETC/ACC, 2009 - Indicators on urban air quality. A review of current methodologies. ETC/ACC Technical paper 2009/8 (http://acm.eionet.europa.eu/reports/ETCACC_TP_2009_8_UrbanAQindicat ors)
- EU, 2004 - Directive 2004/107/EC of the European Parliament and of the Council of 15 December 2004 relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons in ambient air. http://eur-lex.europa.eu/legal content/EN/TXT/?uri=CELEX:32004L0107
- Eurostat, 2014c - Urban Audit. (http://ec.europa.eu/eurostat/web/gisco/geodata/reference data/administrative-units-statistical-units/urban audit).https://www.eea.europa.eu/data-and maps/indicators/exceedance-of-air-quality-limit-3/assessment-5
- https://www.eea.europa.eu/data-and-maps/indicators/exceedance-of-air quality-limit-3/assessment-
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