The ENVIBASE-Project

Documentation / Online Handbook

Air Quality

Description of the Problem

Athens is an urban area with 4 million inhabitants and suffers the same significant air pollution problems shared by all the large cities of the world. These problems are becoming worse because of bad city planning and Athens’ topographical features.

Athens is located along a basin of approximately 400 km² oriented SW-NE, surrounded by high mountains and open to the sea only towards the south. Emissions are due to transport (1.7 million vehicles), scattered industry, and domestic heating. The main pollution burden is confined to the basin, with higher pollution levels usually above and around the city centre and to the west of it, where the majority of the factories are located. The pollution cloud expands according to the wind conditions and the topography. A major influence on certain pollutant concentrations is the strong solar radiation during spring and summer. This is the reason why significant ozone and NO_x concentrations are often recorded in the periphery of the city during the warm season.

The air pollution phenomena in Athens is known as "the nefos," which means "the cloud," a name that underscores its visible character. Visibility impairment during pollution episodes is due to high burdens of aerosol particles, and the yellowish-brown colour of the cloud is due to nitrogen dioxide. The aerosol particles are either emanated from primary emissions (soot or organic compounds) or formed by in-situ processes (most often ammonium sulphates or nitrates). In the case of Athens, the observed particles include those generated by both stationary and mobile sources, but mainly the particles are formed rapidly by gas-to-particle conversion processes.

Mapping the pollution distribution by relying solely on the ground network of monitoring stations presents difficulties. The European Commission's CORINE land cover map indicates the apportionment of stationary sources, including industrial areas, quarries (classified as "mineral extraction"), and domestic heating, comprising the categories "continuous urban fabric" and "discontinuous urban fabric."

The National Law 1650/86 contains the main legal framework for the protection of the environment. The Presidential Decree 1180/81 defines the terms of monitoring the operation of industrial units. Also the Presidential Decree 84/84 defines in a very strict manner the terms for establishment, modernisation, incorporation, and transfer of industrial units located in the greater Athens area and the islands of Salamina and Aigina in order to improve air quality.

Data Sources

The ten stations of the EARTH local monitoring network measure hourly concentrations of sulphur dioxide, nitrogen oxides, ozone, and carbon monoxide. Black smoke and total suspended particulates (TSP) are reported on a 24-hour basis. The black-smoke method captures carbonaceous particles mainly emitted by diesel vehicles and heating, and the TSP method takes into account both black and non-black (i.e. non-carbonaceous) particles. The latter, such as primary aerosols, including dust, are generated by industrial activities or formed in the atmosphere as secondary aerosols by chemical conversion of gaseous pollutants. These secondary, non-black aerosols have the greatest effect on visibility reduction through scattering mechanisms.

Satellite multispectral images provide from time to time synoptic views of how the urban pollution cloud spreads over the Athens basin and is combined with simulation modelling that can help explain the spatial distribution of particulate pollution at single but representative points in time.

Methods

The following measuring methods are used. For carbon monoxide: the "absorption in the infrared" (NDIR), for nitrogen oxides: the "chemical luminescence," for ozone: the "absorption in the UV," for sulphur dioxide: the "fluorescence," and for black smoke: the OECD method.

Trend analysis, monthly and weekly variation, annual means, and 98% values are regularly assessed and reported in annual reports. However, no mapping is carried out by using spatial interpolation of the point measurements. The only pollution maps indicating the spatial distribution of particulate pollutants have been produced on the basis of satellite data and dispersion modelling.

Atmospheric mesoscale dispersion modelling is also carried out by the University of Athens periodically. Finally, remote sensing measurements by Earth observation satellites are used to provide a more objective means for observation of the instantaneous spatial distribution of aerosols over the area.

Results

A database describing the temporal variation of gaseous and particulate pollutants mentioned above has been available since 1980. Compared with previous years, air pollution in Athens showed a general decrease during 1996. As a result, the air pollution in Athens was ranging approximately 94% of the days in 1996 from low to moderate levels. Still there is a problem with ozone levels.

In the framework of the LIFE Community programme, satellite measurements have been used to offer a more objective means of observation of the instantaneous spatial distribution of aerosols, which, in combination with dispersion modelling, suggested solutions for a more judicious locating of ground pollution monitoring stations in the greater Athens area. Data and results produced will be put to optimal use when combined with other information (concerning, e.g., the distribution of pollution sources, the land cover, the geomorphology). The use of a GIS would allow a pollution sensitivity mapping, linking the pollution causes to their environmental effects.

Uses

The use of the above system is also for public information and planning.

Addresses for responsible Agencies