Estimating the exposure of urban popu-lations to air pollution concentrations is cur-rently a rather difficult and uncertain task.
The main problem is the scarcity of concen-tration data and particularly of information on the representativeness of the available data. In general, concentrations of air pollu-tion vary markedly across a city, as has been shown in detailed studies such as that of NO2 in the United Kingdom [47]. Differ-ences in reported concentrations could therefore as easily reflect differences in the location of monitoring sites (in distance from roads, or the city centre, for example) as real differences between air pollution loads in different cities. Unfortunately, much
a Maps 5.1–5.6 referred to in this chapter will be found between Chapters 4 and 5.
b United Nations Economic Commission for Europe Environmental Monitoring and Evalu-ation Programme.
of the urban concentration data available throughout Europe covers only one or a few sites per city, and frequently only a few cities per country. Until more data become avail-able to allow a better characterization of urban air pollution levels, it has to be as-sumed that the existing data reflect a repre-sentative sample of urban air pollution con-centrations across Europe. Nevertheless, the errors of extrapolation based on this assump-tion may be substantial.
Concentration data obtained from several sources have been analysed and empirical re-gression models applied to enable popu-lation exposure calcupopu-lations to be made for those cities for which at least the annual mean concentrations were available. Box 5.1 gives details of data sources and modelling methodology.
Calculations of the exposure of rural populations were based on population den-sities as shown in Map 5.1, and ambient air concentrations calculated with long-range transport models (see Box 5.1).
5.3.2 Sulfur dioxide Urban population exposure
The analysis of SO2 concentrations in the late 1980s was based on data from 162 cities in 21 countries, covering a population of 98 million or 31 % of the total urban population in the Region west of the Urals. The best population coverage, 47 %, was obtained for the CCEE (Map 5.2). For over 20 % of the population with data the annual guideline value for SO2 of 50 µg/m3 was exceeded, and for 3 % of the population levels exceeded 100 µg/m3. The proportion of city residents with high long-term average SO2 levels was markedly higher in the USSR and the CCEE than in western countries (Table 5.1). The comparison of annual mean SO2 levels be-fore and after 1985, for cities with data from both periods, as well as the trends from a number of other cities [51] indicate a de-crease in the average SO2 pollution levels over the decade. The highest annual average
148 Air Pollution
Box 5.1: Assessing exposure to air pollutants
This chapter presents two different approaches to establishing population exposure to out-door air pollution. For rural areas, ambient air concentrations were calculated with long-range transport models. For urban areas, actual measurement data were used as the basis for the analysis.
For the rural population, the exposure was computed based on population densities in the 150 150 km2 EMEP grid and ambient air concentrations in the same grid, calcu-lated with long-range transport models such as EMEP for SO2, NO2 and O3 [48,49] and TRACE for lead [50]. These models calculate ambient rural background concentrations in air, based on first principles and input data on air pollutant emissions, meteorological data and dispersion parameters. Both models have been tested against ambient monitor-ing data. As the results of the models are in general compatible with the observed measurements, both models can be considered reasonably reliable. Moreover, members of the ECE use the EMEP model within their programme on the Convention on Long-range Transboundary Air Pollution.
For exposure of the urban population, ambient concentration data from the following sources were analysed:
(a) the Exchange of Information (EOI) database of the EU;
(b) the database of the ECE Cooperative Programme on Effects on Materials at theNorwe-gian Institute for Air Research (1992);
(c) data returned directly from countries in response to the 1992 WHO Protocols for the Concern for Europe’s Tomorrow data collection exercise, comprising 25 re-sponses received from countries that represent 96 % of the population of Europe and 90 % of the population of the WHO European Region (Austria, Bulgaria, the former Czechoslovakia, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Israel, Italy, Lithuania, the Netherlands, Norway, Poland, Romania, the Russian Federation, Slovenia, the former USSR, Spain, Sweden, Switzerland, the United Kingdom and the former Yugoslavia);
(d) metropolitan area air quality data from the Helsinki Metropolitan Area Council (1992);
(e) The Environment in Europe and North America [51]; and
(f) for O3, the EMEP long-range transport model for photochemical oxidants [49].
The following table summarizes exposure monitoring in urban areas (agglomerations greater than 50 000 inhabitants).
Population of cities with data Number of cities
Number of countries Pollutant Estimates
(millions)
Percentage of total European urban
population
Western countries
CCEE NIS Total
SO2 103 33 100 38 42 180 21
Total SPM 38 12 75 8 4 87 13
Black smoke 63 20 81 11 6 98 13
NO2 91 29 76 35 42 153 18
Lead 47 15 39 55 15 109 16
Box 5.1: Assessing exposure to air pollutants
Data on SO2 came from cities in the following countries: Austria, Bulgaria, the former Czechoslovakia, Denmark, Finland, France, Germany (including two cities in the former German Democratic Republic), Greece, Hungary, Italy, Lithuania, the Netherlands, Nor-way, Poland, Portugal, Romania, the Russian Federation, Spain, Sweden, Switzerland and the United Kingdom.
Data on total SPM came from cities in the following countries: Austria, Bulgaria, the former Czechoslovakia, Denmark, Finland, France, Germany (including two cities in the former German Democratic Republic), Italy, Lithuania, Portugal, Romania, Spain and Switzerland.
Data on black smoke came from cities in the following countries: Austria, Belgium, Fin-land, France, Greece, IreFin-land, Norway, PoFin-land, Portugal, the Russian Federation, Spain, Sweden and the United Kingdom.
Data on NO2 came from cities in the following countries: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Hungary, Lithuania, Netherlands, Poland, Portugal, Romania, the Russian Federation, Spain, Sweden, the United Kingdom and the former Yugoslavia.
Data on lead came from cities in the following countries: Belgium, the former Czechos-lovakia, Denmark, Finland, Germany, Greece, Iceland, Ireland, Lithuania, Norway, Po-land, Romania, the Russian Federation, Sweden, Switzerland and the United Kingdom.
The long-term annual averages were available for the largest number of cities, mostly from responses to the WHO protocols. For some cities, the reported annual mean con-centrations were already an average over several monitoring sites, while several sites were individually reported for one city in other cases. The years for which data were available varied from country to country and even from city to city, and ranged from 1976 to 1990.
Based on the daily or hourly data available for some cities on the European Union's da-tabase, empirical regression models were applied to describe the relationship between an-nual average values and levels above the 24-hour guideline values. These models were then used to estimate levels above the 24-hour guideline values for the cities for which only an-nual average pollution levels were available. Calculations of population exposure were then made for the cities that had at least annual mean concentration data.
Table 5.1: Exposure of the populations of cities with data to annual mean sulfur dioxide (SO2) concentrations
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concentrations reported at the end of the 1980s were in Leipzig (200 µg/m3) and in Saratov, USSR (160 µg/m3).
Over 45 % of the population living in cities with SO2 data experienced days with pollu-tion levels exceeding the daily guideline level of 125 µg/m3 (Table 5.2). In the CCEE and USSR, the levels were higher than 200 µg/
m3 on most of these days, and levels over 125 µg/m3 were more common than in west-ern countries. In Leipzig and Saratov, the 24-hour average concentrations exceeded 125 µg/m3 for 191 and 147 days per year, re-spectively, and levels were above 250 µg/m3 on 77 and 55 days per year, respectively.
In comparison with the early 1980s, the frequency and magnitude of exposure de-creased markedly in all groups, with relatively greater improvement in the west-ern countries. The population in these coun-tries experiencing pollution episodes exceed-ing 250 µg/m3 SO2 decreased from 71 % to 33 % in the 1980s, while the change in the USSR was from 74 % to 51 %. Data were available for only three cities in the CCEE and only for the beginning of the 1980s, which prevented comparison.