Population weighted annual mean SOMO35 in cities

Data source
Ozone data: data compiled from AirBase (3), with additional data provided by the European Environmental Agency (EEA).
Population data: Health for all database HFA-DB (4) and Urban Audit (5).
Percentage of population living in cities: HFA-DB (4).
Processing of ozone data by Frank de Leeuw, ETC ACC, the Netherlands National Institute for Public Health and the Environment, is kindly acknowledged.

Description of data
Ozone monitoring data are submitted by national authorities to AIRBASE. Only data from urban or suburban background monitoring stations, available for at least 75% days of the year, are used in this analysis. Monitoring stations located near heavy traffic or industrial sites were excluded from this analysis. Data quality check and verification of the station’s location classification are carried out by the European Topic Centre on Air and Climate Change (10).

Method of calculating the indicator
Exp = SUM {(Pi/P)*Ci}, where:
Ci = annual mean SOMO35 concentration in sub-population Pi,
P = SUM (Pi), which is the total population in cities with data.

Geographical coverage
All data from cities with ozone measured in urban (or suburban) background locations included in AirBase have been used for this analysis (Table 1). Ozone monitoring is not conducted in most of the non-EU countries, which makes it difficult to assess exposure in that part of the Region.

Period of coverage
Ozone data used for this analysis cover the years 2000–2011. For the EU countries, ozone measurement is mandated under the Directive 2008/50/EC, and previously under Directive 2002/3/EC relating to ozone in ambient air (11). This assures an ongoing monitoring and a gradual increase in coverage of the European population.

Frequency of update
Air quality data (daily concentration of ozone) are submitted by national authorities to AirBase annually. After data quality checks and data processing, the data are made available on line (with a delay of about one year).
City-specific population data are updated less frequently but due to the relative stability of the spatial distribution of population in the countries, the exposure indicator is not affected by the lack of an annual update of population data.

Data quality
Quality assurance and control procedures apply to the ozone data submitted to AirBase (3).