Box 10 I Metabolism of a city: Prague, Czech Republic

Charles Bridge, Prague

Source: H Girardet


Prague, the capital of the Czech Republic, is one of Europe's most beautiful historical cities and part of national and European cultural heritage. With its 500 km2 and a population of 1.2 million, Prague is the largest urban area in the former Czechoslovakia. Unfortunately, it is also a city suffering from serious environmental problems.

Prague's urban metabolism is summarised in Table 10.14. Besides features common to all cities, Prague has some specificities which concern especially the structure of sources of energy and which have important environmental consequences. The total input of anthropogenic energy contained in delivered fuels and electricity to the territory of Prague is about 94 500 TJ (1012J) per year. The final consumption of energy after various transformations (for instance burning of solid and liquid fuels in the heat-and-power plants and boiler stations for district heating systems) is about 80 200 TJ per year. The differences are losses during transformations.

There are more than 200 large emission sources in Prague (large heat-and-power plants and boiler stations with capacity over 5 MW), nearly 10 000 medium sources (boilers in about 5000 small heat plants and boiler stations with 0.2 to 5.0 MW capacity supplying one or several buildings) and more than 200 000 local heating devices (stoves). In addition to these stationary sources, there are about 430 000 motor vehicles in Prague including 350 000 private cars.

The delivery of fuels into the city and their subsequent conversion to heat and energy using rather outdated technical infrastructure have very undesirable effects on the quality of the environment. Total annual emissions from all stationary and mobile sources of pollution in Prague are approximately 56 200 tonnes of sulphur dioxide, 24 000 tonnes of nitrogen oxides, 24 000 tonnes of particulate emissions (dust, fly-ash), 46 200 tonnes of carbon monoxide and 12 000 tonnes of hydrocarbons. The density of emissions in Prague (in tonnes per km2 per year) is several times higher than in the districts of heavily polluted North Bohemia.

The geomorphology of Prague ­ characterised by the valleys of the Vltava (Moldau) and its tributaries and a central kettle-like depression surrounded by hills with total altitude differences of more than 200 metres ­ provides specific microclimatic conditions not favourable to the ventilation and dispersion of air pollution. Thermal inversions occur very often in the lower layers of the atmosphere, and, together with typically low wind velocities, provide the basic conditions for smog episodes, especially during winter. Critical situations occur in the central part of the city where there are thousands of small and medium ground-level emission sources burning solid fuels (very often brown coal of low quality). The ambient air quality is generally poor and health standards are very often breached. Sulphur dioxide concentrations reach the highest levels in the historical core of Prague during the heating season, while nitrogen oxides and airborne aerosol (dust) are more equally distributed over the year.

The characteristics which control the spatial distribution of annual average concentrations of sulphur dioxide in ambient air in Prague (Map 10.3d) are illustrated in Maps 10.3a, b and c. The highest concentrations are, as a rule, in the historical core of Prague, the 'Old Town'. This is a result of the combination of geomorphology, climate, energy consumption patterns and density of emission sources.

The urban areas with the highest consumption of anthropogenic energy per unit of territory are shown in Map 10.3a. The red areas, mostly in the centre of Prague, show energy consumption above 10 TJ per hectare per year (the map may also be seen as one of 'energy consumption density' or 'intensity of energy metabolism'). Since the annual input of solar radiation in Prague is about 30 TJ per hectare per year, the marked areas have an annual consumption of anthropogenic energy equal to or larger than one third of annual solar energy input. During winter months the input of anthropogenic energy in such areas is several times higher than the solar one.

The production of waste heat together with accumulation of solar radiation energy in buildings and other urban structures creates the 'urban heat island' effect (see Box 10E) which is typical of the urban climate. The red areas on the map can be called 'the heart' of the urban heat island in Prague.

Map 10.3b shows the natural climatic conditions in Prague classified as best or worst zones for insolation, ventilation and occurrence of thermal inversions. The worst climatic conditions are at the bottom of the Vltava valley and include the lower parts of the historical core of Prague (protected by law as the Prague urban reserve).

The map of sulphur dioxide (SO2) emission density, expressed in tonnes per square kilometre per year (Map 10.3c) shows very clearly that the centre of the city is heavily burdened, because of the great number of small and medium sources located there. Other areas of the city with high density of sulphur dioxide emissions are those where large industrial plants are located.

The annual average sulphur dioxide concentrations in Prague in 1990 varied between 31 and 110 µg/m3 and the maximum concentrations between 184 and 681 µg/m3. The relative number of measurements exceeding the daily health standard of 150 µ/m3 was between 0.3 and 27.1 per cent. The results for nitrogen oxides were even worse, with average annual concentrations of 37 to 134 µg/m3 and the relative number of measurements above the daily recommended limit of 100 µg/m3 from 5.2 to 61 per cent. Although nitrogen oxides as well as airborne dust have their maximum concentrations also in the inner city, they are more influenced by other sources. For nitrogen oxides, automobile traffic is an important source.

Air pollution in Prague causes high economic losses. The annual losses due to accelerated corrosion, increased occurrence of diseases in Prague inhabitants and damage to vegetation were estimated to be almost 2000 million Czech crowns ($70 million).

The solution of the problems caused by energy conversion and use in Prague faces no technical obstacles.The efforts fail because of lack of finance and because of serious shortcomings in organisation at all levels. Moreover, the necessary economic instruments for pollution abatement are still missing.

The major goal is to switch energy sources in the city from solid and liquid fuels to electricity, natural gas (with proper low-emission combustion technologies) and district-wide central heating. The priority is being given to the historical core of Prague. New legislation (Air Protection Act from 1991) should help state and municipal administration in these efforts.

Source: City of Prague


Table 10.14 - Selected data, City of Prague, 1991

Source: City of Prague, personal communication

Area = 494.8 km2
Population = 1 212 010 (1991)
Consumption of materials (tonnes per year)
(approximate data for 1985)
Excavated rock and soil 11 000 000
Sand, gravel, building stone5 900 000
Asphalted gravel for roads1 800 000
Bricks260 000
Other construction materials8 600 000
Iron, steel4 200 000
Other metals35 000
Paper300 000
Chemicals160 000
Paints70 000
Plastics55 000
Food including packaging4 100 000
Beverages500 000
Consumption of energy (TJ per year)
Type of fuel
or energy
Delivery on the
territory of the city
Consumption after
transformations
Coke 10 665 (11.3%) 10 665 (13.3%)
Other solid fuels 18 360 (19.4%) 8110 (10.1%)
Liquid fuels 13 087 (13.8%) 8270 (10.3%)
Natural gas 37 735 (40%) 19 122 (23.9%)
Electricity 14 578 (15.4%) 13 394 (16.7%)
District heating
(centralised heating)
­ 20 566 (25.7%)
Total consumption 94 425 (100%) 80 127 (100%)
Transport
Number of all motor-vehicles430 000
Number of passenger cars340 000
Number of people per car3.6
Transportation mode ­ percentage of journeys done by public transport in an average working day:
- for all intra-urban journeys75%
- for all extra-urban Journeys58%
Percentage of transport means in the public transport:
- underground railway36%
- tram33%
- bus31%
Road network:
Total length in the city2 700 km
Density5.4 km roads per km2 urban territory
Landuse (data for 1980)
(% of the city)
Residential17.3
Industrial4.5
Agricultural39.6
Green spaces18.7
Sport and recreation1.4
Public amenties (culture, education,
commerce, services, health and
social care)
3.3
Transport and technical facilities 7.9
Water reservoirs, rivers, ponds 1.7
Other 5.6


Map 10.2 - Landuse in Prague

Source: City of Prague


Map 10.3a ­ d Spatial distribution of annual average concentrations of SO2 in ambient air in Prague

Source: City of Prague, personal communication