LA PSICOLOGIA SOCIAL

6.2.1. Indicators for urban air quality

Several endpoints for evaluating the results can be defined in a sensitivity analysis of urban air quality:

• Compliance with air quality guidelines. The air quality guidelines used in this study are all related to the protection of human health; they are based on adopted or proposed daughter directives (EC, 1999d and e).

• Population exposure. Population exposure can be expressed in several ways, giving emphasis to different features of exceedances. The simplest way is to calculate the number of inhabitants exposed to concentrations above guidelines. For evaluating the extent of exceedance of environmental guidelines, the population exposure above a threshold (PET) is defined as:

where Ci,nis the concentration in excess of the threshold value T incity n during exceedance i; Ncity is the number of cities where an exceedance is calculated; En is the number of exceedances; and popn is the population of city n. PET is expressed in persons x micrograms per cubic metre (µg/m3_{). PET values are largely determined by concentrations} in the upper tail of the frequency distribution.

• Impact on human health. A quantitative estimate of the impact on human health can be based on the calculation of the attributable proportion (Krzyzanowski, 1997). This indicates the fraction of the health outcome that can be attributed to the exposure in a given population (provided that there is a causal association between the exposure and the health outcome). Relative risk estimates for daily mortality associated with sulphur dioxide (SO₂) and nitrogen dioxide (NO₂) exposure are taken from the updated WHO Air quality guidelines for Europe (WHO, 1997). For both components a no-health-effect threshold value of 10 µg/ m3 _{is assumed. In contrast to the PET value, almost the full concentration frequency} distribution contributes to the excess rate.

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6.2.2. Air pollution models

In the AOP II GEA study, three air pollution models have been used for the calculation of air quality parameters from urban emissions. These are:

• The cQ model (Olsthoorn et al., 1999) for ‘inert’ species, where sufficient monitoring data were available, i.e. nitrogen oxides (NO_x)/NO₂, SO₂ and respirable particulate matter with aerodynamic diameter between 2.5 and 10 micrometres (PM₁₀).

• The UAQAM model (van Pul et al., 1996) for ‘inert’ species in all cities, i.e. NO_x/NO₂, SO₂ and PM₁₀, lead (Pb), carbon monoxide (CO) and benzene.

• The OFIS model (Sahm and Moussiopoulos, 1999), which was applied to calculate ozone concentrations for a limited number of cities.

In the present study an updated and improved version of the OFIS model (Moussiopoulos and Sahm, 1998) is applied to assess urban ozone levels in numerous large European cities. Compared to the model version used for the needs of Environment in the European Union at the turn of the century (EEA 1999a, hereafter referred to as the EEUTC report) this updated version takes into account local circulation systems (such as sea breeze in coastal areas) and emissions from neighbouring cities, based on data derived from the Corinair 90 database of the EEA/ETC-AE (EEA, 1996a). Moreover, background boundary layer concentrations are computed with a 20-layer box model embedded in OFIS, instead of the 3-layer box model that was used in the previous model version.

The UAQAM model has been extended with a procedure to estimate a health indicator (see below). In comparison to the AOP II applications, the meteorological database used has been improved and extended. In the current application, the cQ model has not been included.

All models calculate the contribution to the urban background concentrations resulting from the local, urban emissions. The regional background contributions from emissions outside the urban area considered were derived from the EMEP (cooperative programme for monitoring and evaluation of long-range transmission of air pollutants in Europe) acidifying (Tsyro, 1998) and photochemical model (Simpson, 1992 and 1993) or from the TREND model (van Jaarsveld, 1995). In UAQAM simulations daily concentrations obtained from the routine applications of the EMEP lagrangian model are used for the years, 1991–95.

Concentrations for the reference years 2010 and 2020 are estimated using a reduction factor calculated at a national level from the published SO_x and NO_x source-receptor matrices. The OFIS simulations were performed for about 180 individual days with meteorological

conditions as in period 1 (April–30 September 1990). For this period, meteorological data and EMEP model results (regional background concentrations) are available at a spatial resolution of 150 kilometres (km) and a temporal resolution of six hours. The EMEP results refer to the emission situation in 1990 and the one projected for 2010 using the AOP II emission scenario.

Although in regional and urban modelling the emission information is prepared consistently (see above), the urban air quality is not linked directly with the air quality part of the RAINS model.

6.2.3. Selection of cities

The selection of cities used in the Auto-Oil II Programme yielded 192 conurbations in the 15 Member States of the European Union. For the ShAIR scenario this set has been extended with cities in EEA member states and in accession countries with more than 100 000

inhabitants (UN, 1997), since violation of air quality guidelines is primarily expected in larger conurbations with a high emission density. In each country at least one city is selected. The final list contains 309 conurbations in 30 countries, with a total population of 146 million inhabitants. An overview of selected cities is presented in Table 6.1.

The built-up area of the selected cities has been estimated by a procedure developed by the European topic centre on land cover (ETC-LC, 1997), using detailed land-use and land-cover information.