V.1 THE CAPITAL CITY OF PRAGUE

From the perspective of ambient air pollution, the capital city of Prague is ranked among the most burdened areas of the Czech Republic. This is the result of the interaction of a number of natural factors, particularly the high concentration of inhabitants and the dense transport network connected with it.

The specific location of Prague in the varied terrain of the Prague basin significantly affects the climatic and dispersion conditions of its territory (Ložek et al. 2005). The Vltava river valley is usually poorly ventilated, and especially in the cold half of the year, there are favourable conditions for temperature inversions, when markedly warmer air is shifted above cooler air near the ground. Heavy cold air remains close to the ground and thus prevents pollutants from dispersing into upper layers of the atmosphere. This results in increased pollutant concentrations in the still, ground-level layer of air (Bednář, Zikmunda 1985).

Deteriorated ambient air quality in Prague is connected mainly with significant traffic loads. Prague represents, due to its geographical position, not only the main junction of the road network in the Czech Republic, but also a significant crossroads of international transit transport. Multiple main routes lead directly through the centre of Prague. The current communication network in the inner city, however, is unable to accommodate such a huge concentration of traffic, leading to frequent collapses. The situation is supposed to be partly solved primarily by the completion of ring roads around Prague, by a considerable reduction of private cars in the most affected areas, and emphasis on the railway and public transport (IPR Praha 2012).

With regard to its historical development, Prague also has a developed industrial infrastructure (IPR Praha 2012). In spite of the fact that numerous industrial plants that were not complying with the set conditions for their operation have recently been closed down or had to reduce their production, there is a growing focus on the sector of services. Consequently, new commercial and administrative centres have been built, placing high demands on transport services and the consumption of energies, incl. heating.

The consumption of fossil fuels for household heating in family houses, mainly in the city outskirts, has a considerable influence on the current air pollution situation in Prague.

V.1.1 Air quality in the agglomeration of Prague
 

Suspended particles PM₁₀ and PM_2.5

In 2014 the limit value for the average 24-hour concentration of PM₁₀ (the value 50 µg.m^-3 must not be exceeded more than 35 times in one year) was exceeded in the territory of the Prague agglomeration at 6 of 15 localities with a sufficient number of data for the evaluation. Five of the above localities are classified as traffic localities, and one is classified as a suburban background locality. It can also be stated that 2014 ended the decreasing trend in average 24-hour concentrations calculated separately for traffic and background (urban and suburban) stations. Thus, for the first time since 2010, a slight increase in PM₁₀ concentrations occurred. The difference between the average 24-hour concentration at traffic stations and at background stations continues to decrease as well; in 2014 it was lower than 3 µg.m^-3 (Fig. V.1.1).

In 2014, similarly as in the previous years, the annual PM₁₀ limit value (40 µg.m^-3) was not exceeded at any locality of 16 localities relevant for the evaluation of annual concentrations.

As a rule, high concentrations of suspended PM₁₀ and PM_2.5 particles and the most frequent exceedances of 24-hour limit value for PM₁₀ are reached in the cold period of the year due to higher emissions of TSP caused both by higher intensity of heating (incl. local heating) and higher emissions from traffic (increased abrasion of the road surface caused by road gritting and subsequent re-suspension of the abraded material; EC 2011) as well as due to less favourable meteorological conditions for the dispersion of pollutants. In 2014 the agglomeration of Prague experienced the highest number of exceedances of the 24-hour limit value for, namely in the months of March, January, April, November and October (Fig. V.1.2). In these months, more frequent occurrences of unfavourable dispersion conditions were observed compared to the distribution of pollen dispersal conditions in other months (Fig. III.3).

The limit value for average annual concentrations of suspended PM_2.5 particles was exceeded in 2014 at one of five stations with a sufficient number of data for the evaluation. An overlimit concentration (25.6 µg.m^-3) was measured at the station Prague 2-Legerova, classified as a traffic station (hot spot). Similarly as in the previous years, the limit value was not exceeded at the remaining localities (Prague 2-Riegrovy sady, Prague 4-Libuš, Prague 5-Smíchov and Prague 5-Stodůlky; Fig. V.1.3).
The trend of air pollution characteristics for PM₁₀ is evaluated on the basis of data from stations for which there exists a complete time series starting in the year 2000 (Fig. V.2). A steep drop of PM₁₀ concentrations was recorded from 1996 to 1999 (e.g. ČHMÚ 2014c). After 1999 the concentrations increased again, and in the period after the year 2000, in the year 2003, the so-far maximum levels are reached due to unfavourable dispersion conditions in February and December and due to subnormal precipitation amounts. Since the year 2003 the overall trend of air pollution has had a decreasing character; nevertheless, there were fluctuations in individual years, mainly due to meteorological and dispersion conditions. Higher PM₁₀ concentrations were measured, for instance, in the years 2006, 2010 and 2011. In the last three years, the 36^th highest daily PM₁₀ concentration of PM₁₀ does not exhibit any marked trend. The average annual PM₁₀ concentration remains below the level of the respective limit value starting from the year 2004. However, the 36^th highest daily concentration of PM₁₀ remains below its limit set since and including 2007; in some years, such as 2010 and 2011, it nevertheless approaches this daily limit value.

The trend of pollution characteristics for PM_2.5 is assessed based on data from stations for which there exists a complete time series since the year 2005; the annual average concentration reached its highest values in 2005, 2006 and 2010; in the years 2005 and 2006 the annual concentration (on average across all stations) even exceeded the pollution limit value. Since 2011 the trend in annual PM_2.5 concentrations has been stable.

Nitrogen dioxide

The hourly limit of 200 µg.m^-3 was not exceeded in 2014 at any of the 15 localities of those which are relevant for the assessment. At the locality Prague 2-Legerova, the pollution limit was exceeded five times. The permissible number of exceedances is 18. The hourly limit value for NO₂ (200 µg.m^-3) was thus not exceeded at any of these localities in 2014.

With regard to exceedances of the limit value in Prague, there is a problem mainly with the aforementioned traffic station Prague 2-Legerova (hot spot) where NO₂ has been measured since 2003. This station focuses at monitoring air pollution caused by traffic. The hourly limit value was not exceeded at this locality since 2012 (Fig. V.1.4).

The annual limit value for NO₂ (40 µg.m^-3) was exceeded at two out of the 14 localities in the territory of the Prague agglomeration. These localities were Prague 2-Legerova (the annual average concentration reached the value of 51.1 µg.m^-3) and Prague 5-Smíchov (41.3 µg.m^-3).

The trend of air pollution characteristics for NO₂ is evaluated on the basis of data from stations for which there exists a complete time series starting in the year 2000 (Fig. V.1). The downward trend of NO₂ concentrations of the 90s (e.g. ČHMÚ 2014c) stopped in 2000 and, conversely, NO₂ concentrations were increasing up until 2003 when the concentration levels recorded were similar to those measured in 1996. The higher concentrations of NO₂ in 2003 were caused both by unfavourable dispersion conditions in February and December and by subnormal precipitation amounts. Since 2003 the air pollution characteristics of NO₂ have not shown any marked trends. On the whole they are decreasing, but the year-on-year comparison reveals fluctuations, which are mainly caused by the prevailing meteorological and dispersion conditions. An increase of both the annual average concentration and the 19^th highest 1-hour concentration was recorded in 2006 and 2011. Since 2011, air pollution characteristics of NO₂ have had a very slight decreasing trend, with the exception of the year 2014, when the 19^th highest hourly concentration increased compared to the previous year. From the beginning of the evaluated period, air pollution characteristics of NO₂ remain below their respective limit values. It can be assumed, however, that pollution limits can be exceeded also at other localities exposed to traffic where no measurements are carried out.

Benzo[a]pyrene

Elevated concentrations of benzo[a]pyrene are still causing problems in the Prague agglomeration. In 2014 the limit value for the annual average concentration of benzo[a]pyrene was exceeded at the station Praha 4-Libuš. At the station Prague 10-Šrobárova, the annual average concentration varies just below the annual limit (0.95 ng.m^-3). Benzo[a]pyrene concentrations in the evaluated period starting with the year 2000 reached its highest level in 2006, then decreased until 2009, and since 2010 they do not exhibit any marked trend. Since the measurements of benzo[a]pyrene concentrations commenced, they exceeded the limit value every year at at least one monitoring station in the Prague agglomeration (Fig. V.1.5).

Ground-level ozone

In 2014 (on average for 3 years from 2012 until 2014), the limit value for ground-level ozone was not exceeded at any of the six stations in the territory of the Prague agglomeration. The highest number of exceedances of the limit value was recorded at the locality Prague 6-Suchdol where the 26^th highest maximum daily 8-hour running average reached 119.4 µg.m^-3 (three-year average). Exceedances of the limit value at this locality had so far occurred every year within the evaluated period. In 2014, however, the limit value was not exceeded for the first time over the monitored period. At this station, the limit value was exceeded 23.3 times on average over three years, the permissible number of exceedances being 25 (Fig. V.1.6). The lowest concentrations are measured at the traffic station Prague 9-Vysočany, which corresponds to the formation of ground-level ozone and the course of its concentrations (Chapter IV.4.3).

Other pollutants

As concerns other pollutants listed in the legislation (CO, SO₂, benzene and heavy metals), the limit values have in the long term been successfully met in the agglomeration of Prague. Concentrations of SO₂, Ni and Cd exceeded their respective limit values at several stations in the 90s; after the year 2000, above-the-limit annual average concentrations of arsenic occurred at the station Prague 5-Řeporyje for the last time in 2011. Nevertheless, the concentrations of these substances also respond to the prevailing meteorological and dispersion conditions, and thus increases of several air pollution characteristics of these pollutants were recorded e.g. in the years 2003, 2006, 2010 or 2011.

V.1.2 Emissions in the agglomeration of Prague

At present, there are 2,050 individually registered sources of ambient air pollution in the territory of the Prague agglomeration, included in the REZZO 1 and REZZO 2 databases. Only a few of them, however, are contributing significantly to total emissions, primarily the cement plant Cementárna Radotín and the heating plant Teplárna Malešice (Pražská teplárenská, a. s. – PT, a. s.), the ZEVO Malešice (Pražské služby, a. s.), other thermal energy sources of PT, a. s., and industrial plants such as the tyre manufacturer MITAS, a.s. In the recent period, the share of emissions from the production of electric energy in cogeneration units has also increased (e.g. ÚČOV PVaK and TEDOM Daewo-Avia Letňany). According to SLDB 2011 outputs, most households are heated by central sources (ca 52 % of flats), followed by gas boiler rooms and local gas boilers (altogether ca 31 % of flats). A significant share is contributed by electrical heating (about 5 %) and other types of heating that are difficult to classify (a relatively high share of about 10 %). Only in a small part of the housing stock, primarily in the city outskirts, coal, wood and coke are used for heating. Similarly, the majority of community sector buildings are connected to central heat sources or have their own gas boiler rooms.

In the period 2002–2013, all monitored emissions decreased in the above significant sources. As concerns heat generating sources, the decrease is connected with the implementation of the large-scale project interlinking the thermal energy supply system Mělník-Prague, which was established in 1995. The essential decrease of SO₂ emissions is related to reducing the amount of hard coal combusted in the heating plant in Malešice (starting from 2011).

In the nationwide perspective, the emission load of Prague is rather specific. Most sources monitored as point sources and area sources operated in the territory of Prague have minor significance, and the highest share of emissions is caused by traffic (Fig. V.1.9). With regard to the fact that significant sources usually have tall chimneys, their share in air pollution is often recorded in areas outside Prague.

The decrease in reported TSP emissions of REZZO 2 sources is in fact influenced to a certain extent by the change of the reporting methodology as concerns emissions from quarries based on the implementation of the provision on the method of ascertaining the amount of emissions.

V.1.3 Conclusion

The capital city of Prague is an area where a lot of people are exposed to ambient air pollution. In the agglomeration of Prague, the limit values for suspended particles, nitrogen dioxide and benzo[a]pyrene are exceeded in the long term. The limit value for ground-level ozone is usually exceeded in the outskirts of Prague. Most of the exceedances are connected with significant traffic loads of the capital, but also with household heating, mainly in built-up areas by family houses. The share of mobile sources in total emissions of TSP in the agglomeration of Prague amounts to more than 85 %, in total emissions of Nox to approximately 75 %.

In the Prague agglomeration in 2014, the limit value was exceeded for the average 24-hour concentration of PM₁₀ and the annual average concentration of PM_2.5, NO₂ and benzo[a]pyrene. Since 2011, annual average concentrations of PM₁₀ at monitoring stations have stayed below the limit. In 2014, for the first time over the monitored period, ground-level ozone did not exceed its limit. As concerns other pollutants, meeting their respective limit values does not pose a problem.

 

Fig. V.1.1 Number of exceedances of 24-hour PM₁₀ limit value and the 36^th highest 24-hour concentration PM₁₀ at individual types of stations, agglomeration of Prague, 2006–2014

Fig. V.1.2 Number of days with concentrations of PM₁₀ > 50 µg.m^-3 in individual months, incl. total number of exceedances, agglomeration of Prague, 2014

Fig. V.1.3 Average annual PM_2.5 concentrations, agglomeration of Prague, 2004–2014

Fig. V.1.4 Numbers of exceedances of the hourly limit value for NO₂ at the traffic station Prague 2-Legerova (hot spot), agglomeration of Prague, 2003–2014

Fig. V.1.5 Average annual benzo[a]pyrene concentrations, agglomeration of Prague, 2000–2014

Fig. V.1.6 Numbers of exceedances of the limit value of O₃ in the average for three years, agglomeration of Prague, 2006–2014

Fig. V.1.7 Field of the annual concentration of NO₂, agglomeration of Prague, 2014

Fig. V.1.8 Field of the 36^th highest 24-hour concentration of PM₁₀, agglomeration of Prague, 2014

Fig. V.1.9 Emissions of selected pollutants listed according to REZZO, agglomeration of Prague