II.5 Evaluation of the smog regulation systems operation on the territory of the Czech Republic in 2008

The first two and the last two winter months of the year 2008 had above-the-normal temperatures. In January, the average temperature was 1.3 �C with the deviation from the normal +4.1 �C and similarly, the February average temperature reached 2.3 �C with the deviation +3.4 �C. November 2008 with the average temperature 4.6 �C and December 2008 with the temperature 0.7 �C differed from the normal by +1.9 and by +1.7 �C respectively. According to the measurement at the station Prague-Libuš the months January and February were markedly, and November and December 2008 slightly above the normal. In the total, 76.9 % of the length of the monitored period recorded positive deviations of air temperatures form the long-term normal. The monitored year had three markedly warm periods: 18.–21.1.2008 (maximum deviation from the normal +10.9 �C), 27.–29.1.2008 (maximum deviation from the normal +6.0 �C) and 21.–27.2.2008 (maximum deviation from the normal +11.7 �C). Similarly, there were two cold periods: 22.–25.2.2008 (maximum deviation from the normal –3.1 �C) and 26.–31.12.2008 (maximum deviation from the normal –5.9 �C). The average daily air temperatures from 1.1. to 29.2.2008 and from 1.11. to 31.12.2008 and their long-term normal at the station Prague-Libuš are presented in Figs. II.5.1 and II.5.2. As for precipitation, all 4 months were weakly to moderately below the normal. The highest amount of precipitation, as compared with the long-term normal – 37 mm – was recorded in January 2008 and represents 90 % of the normal. As for the absolute value, the highest amount was recorded in November 2008 – 43 mm, which represents 87 % of the normal. The lowest amount – 27 mm – was measured in February 2008, which represents 72 % of the long-term normal.

Anticyclonic situations in January–February and November–December 2009 occurred in 28.1 % of the length of this time interval and their relative frequency for the above months was unsteady and ranged between 16.1 and 38.7 %. The highest relative frequency of the occurrence of anticyclonic situations (38.7 %) was recorded in December 2008 and the lowest one (16.1 %) in January 2008. In February 2008 the relative frequency reached 31.0 % and in November 26.7 %. The markedly warm periods in January and February 2008 were caused by the occurrence of western cyclonic situation of the type Wc (11 days) and northwest cyclonic situation of the type NWc (2 days), characteristic in winter period by the influx of relatively warm air from the central Atlantic. The markedly cold periods in November and December 2008 were caused by the anticyclone in the central Europe, type A (3 days), eastern and northeastern anticyclonic situation of the types Ea and NEa (3 days), northern cyclonic type Nc and travelling troughs of low pressure, type Bp. All the mentioned situations are characteristic by negative temperature deviations in the winter period.

The average hourly SO₂ concentration exceeding the alert threshold 250 μg.m^-3 was registered at 13 AIM stations in 2008, out of which 4 stations were in the Krušné hory Mts., with the exception of January and August. The exceedance in three subsequent hours was recorded only at the station Ostrava-Zábřeh with the maximum value 959.7 μg.m^-3. In the Krušné hory Mts. there was a contact of smoke plume with the terrain, in the remaining cases the high concentrations were caused by local sources of air pollution.
The limit value 250 μg.m^-3 for NO₂ was exceeded at the station Legerova (in total 53 days), out of which six cases were in three subsequent hours. The highest measured concentration was 280.4 μg.m^-3. The period with the highest NO₂ concentrations at the station Legerova is depicted in Fig. II.5.3. Exceedances of 1-hour averages occurred also at the following stations: Prague 10-Průmyslová, in Ústí nad Orlicí, in Liberec and in Uherské Hradiště. Both in SO₂ and NO₂ concentrations there were only short-term exceedances of the set limits and each time the pollutants concentrations quickly decreased and, consequently, the conditions for the announcement of the SVRS signals were not fulfilled.

According to the analysis of maximum daily temperatures at the station Prague-Libuš the period from 1 April to 30 September 2008 was slightly above the normal with the deviation +1.3 �C, but markedly fluctuating as for the temperature. Temperature deviations from the normal ranged in the interval from +10.7 �C to –13.0 �C. The highest average monthly temperature deviation in the monitored period was recorded in June (+2.6 �C), the lowest one in September (–0.2 �C); in the remaining months the deviations ranged between +0.5 �C to +1.1 �C. There were 14 days with the temperatures exceeding 30 �C in the monitored period and the highest value (32.2 �C) was measured on 1.8.2008.

Meteorological conditions for the formation of tropospheric ozone from 1 April to 30 September 2008 were not much favourable, the most suitable conditions were in July when on two subsequent days the concentrations exceeding 180 μg.m^-3 occurred, and on 3.7.2008 the station Rudolice v Horách measured the concentration 189 μg.m^-3 (Fig. II.5.4).

On 28 June 2008 there occurred the cyclone 1010 hPa near Nova Scotia, which deepened markedly while moving eastwards and on 30 June 2008 its centre with the value 985 hPa was situated west of the British Islands. On its front side there increased the influx of warm air to western and central Europe, which culminated on 2 July and partly on 3 July 2008. On 1 July the anticyclone 1020 hPa was created above central Europe with its centre above northern Poland; while moving eastwards it disintegrated. On 3 July in the afternoon the cold front accompanied by strong precipitation entered Bohemia. During the night the front moved to Moravia.

On 28 and 29 June 2008 the weather was prevailingly somewhat clear, with local precipitation beyond measurements. Maximum daily temperatures in Bohemia increased from 23–27 �C to 27–32 �C, in Moravia the temperatures were approx. by 1–2 �C lower. On 30 June the weather in eastern Moravia and in southern Bohemia was temporarily cloudy, with local precipitation up to 20 mm, the rest of the territory had clear to somewhat clear weather. Maximum daily temperatures increased to 26–30 �C in Bohemia, in Moravia the temperatures were lower by about 1 �C. On 1 and 2 July the weather in the territory of the Czech Republic was almost clear with maximum daily temperatures 26–32 �C in Bohemia, and in Moravia by 1–2 �C lower. On 3 July the weather was clear to somewhat clear (in Bohemia in the morning, in Moravia for the whole day), with maximum daily temperatures 26–33 �C. The cold front moved across Bohemia in the afternoon and across Moravia during the night, and it brought the precipitation of 5–20 mm on the most of the territory of the Czech Republic, locally 30–50 mm; the station Jevíčko recorded 67 mm. On the following day the temperatures decreased to 20–25 �C in the whole republic.

The increased ozone concentrations can be expected with the occurrence of high air temperatures, when the weather is clear or somewhat clear with low wind velocities. From 1 April to 30 September 2008 the station Prague-Libuš recorded 3 periods, in which for 3 and more days the afternoon temperatures reached more than 27 �C. The overview of the periods with three or more days with temperatures exceeding 27 �C and the respective measured maximum O₃ concentrations are presented in the table II.5.2.

The table shows that the most suitable conditions for the formation of tropospheric ozone were theoretically from 26.7. to 1.8.2008, but O₃ concentrations reached only 173 μg.m^-3. This was caused by frequent exchange of air masses above the territory of the Czech Republic (between 26.7. and 1.8.2008 four frontal disturbances moved across the territory of the Czech Republic). One of the important conditions for the occurrence of high ozone concentrations is the long stay of the air mass above a certain area. Starting from 28 June 2008 the maximum daily temperatures and ozone concentrations began to increase in the Czech Republic. On 2.7.2008 5 stations (Žatec, Rudolice v Horách, Most, Červená and Přebuz) recorded the exceedance of the alert threshold limit value 180 μg.m^-3; the highest value 186 μg.m^-3 was measured in Žatec (Fig. II.5.5). On the following day the alert threshold limit was exceeded only at the station Rudolice v Horách (189 μg.m^-3), but only for 1 hour. None of the above stations recorded the concentrations above 180 μg.m^-3 for three hours and more, and consequently, the conditions for the announcement of the warning signal were not fulfilled.

Tab. II.5.1 The overview of O₃ concentrations above 180 μg.m^-3 lasting 3 hours and more

Tab. II.5.2 Overview of the periods with air temperatures above 27 �C for 3 or more days, and of the respective measured maximum ground-level ozone concentrations

Fig. II.5.1 Course of daily average air temperatures and the long-term normal, Prague-Libuš, 1.1.–29.2.2008

Fig. II.5.2 Course of daily average air temperatures and the long-term normal, Prague-Libuš, 1.11.–31.12.2008

Fig. II.5.3 Average hourly NO₂ concentrations at the station Prague 2-Legerova, 20.7.–23.8.2008

Fig. II.5.4 Course of maximum daily air temperatures, their normal and daily sums of precipitation at the station Prague-Libuš. Occurrence of ozone concentrations exceeding 180 μg.m^-3 in the territory of the Czech Republic, 1.4.–30.9.2008

Fig. II.5.5 Spatial distribution of maximum daily concentrations of ground-level ozone on the territory of the Czech Republic, 2.7.2008