Graphic Yearbook

VI. SMOG WARNING AND REGULATORY SYSTEM

The CHMI, authorized by the Ministry of the Environment, operates the Smog Warning and Regulatory System (SWRS). Information provided through this system serves both for informing about extraordinary levels of ambient air pollution (smog situations) and for the regulation (reduction) of pollutants released from selected sources markedly influencing ambient air quality in the given territory. The monitored pollutants include PM₁₀ fraction suspended particles, sulphur dioxide (SO₂), nitrogen dioxide (NO₂) and ground-level (tropospheric) ozone (O₃).

Starting from 1 September 2012, the operation of the SWRS is set down by the Air Protection Act and by Decree No. 330/2012 Coll. The main changes in comparison to the previous legislation are described in the CHMI yearbook for the year 2012 (CHMI 2013a) and an article by Juras and Vlček (2013). Smog situations and regulatory notices (alerts for ozone) are announced on the basis of exceedances of threshold values.

The current system of rules of the SWRS (Table VI.1) results in the practice that smog situations and regulatory notices for PM₁₀ are announced and cancelled with a delay relative to the actual development of concentrations. Therefore, the CHMI prepared a draft amendment of Annex No. 6 to the Air Protection Act aimed at the elimination of this drawback (Vlček et al. 2015).

The current list of regions and stations representative of PM₁₀, SO₂ and NO₂ levels (Fig. VI.1, VI.3, VI.4) is stipulated by the Journal of the Ministry of the Environment¹, and in the case of O₃ (Fig. VI.2), it is specified by the CHMI director’s directive on the implementation of the Smog Warning and Regulatory System (SWRS) on the territory of the Czech Republic. In 2014 the list published in the Journal of the Ministry of the Environment No. 9, 10/2013 applied for PM₁₀, SO₂ and NO₂. Applicable since November 2014 was the list published in the Bulletin of the Ministry of the Environment No. 6/2014 (in the territory of the Brno agglomeration, the representative station for PM₁₀ and NO₂ Brno-Lány was replaced by the urban background stations Brno-Arboretum and Brno-Dětská nemocnice). Throughout the year, the list provided by the CHMI director’s directive No. 2013/05 applied for O₃.

PM₁₀, SO₂ and NO₂

In 2014 smog situations were announced only due to the exceedance of threshold values for PM₁₀ suspended particles. Similarly as in the previous years, no smog situation was announced because of for SO₂ and NO₂. In 2014 neither the informative nor the regulatory threshold value for NO₂ was exceeded at any of the representative stations. In the case of SO₂, there were isolated exceedances of the informative threshold value (in Sokolov on 9 December, in Přerov on 30 June and in České Budějovice on 28 and 29 September). A regulatory notice was not issued, however, because in neither case was the informative threshold value exceeded in three consecutive hours. An exceptional situation occurred on the night of 28 to 29 October at the Přerov station, where one-hour concentrations of SO₂ exceeded the regulatory threshold value between 10 pm on 28 October and 4 am on 29 October with a maximum of 12,687 μg.m^-3. A regulatory notice was not issued. Later it was confirmed that the high concentrations were caused by resumed production at the company Precheza, a. s.; a regulatory notice would thus not serve its purpose.

Nine smog situations were announced in 2014 due to high concentrations of suspended PM₁₀ particles, lasting a total of 501 hours (21 days), and one regulatory notice was issued, lasting 37 hours (Table VI.2). Four of them were announced in the first decade of December in the O/K/F–M agglomeration without the Třinec region, in the Třinec region, in the Moravia-Silesia zone and in central Moravia when strongly unfavourable dispersion conditions caused a severe deterioration of air quality. In this period, a regulatory notice lasting 37 hours was also issued in the Moravia-Silesia zone (Table VI.3). The overall small number of announced smog situations was associated with more favourable dispersion conditions in the cold part of the year, which are a consequence of abnormally warm weather and a larger number of frontal systems crossing the territory of the Czech Republic.

Besides smog situations, all SWRS stations also recorded exceedances of the daily limit value for PM₁₀. The best situation was in the South Bohemia region (3.8 % of days) and the Vysočina region (4.7 % of days). On the contrary, the greatest number of days with exceedances of the daily limit value was recorded in the O/K/F-M agglomeration without the Třinec area (37 % of days), in the Ústí nad Labem region and in the zone of Central Bohemia (Table VI.4).

Ground-level ozone

In 2014 two smog situations were announced due to high concentrations of ground-level ozone O₃). Their total duration was 42 hours (2 days) and applied to the O/K/F-M agglomeration and the agglomeration of Prague (Table VI.5). Both occurred at the turn of the first and second decade of June (Table VI.6). The conditions for issuing a warning were not met in any of the SWRS regions.

Besides the exceedance of the threshold values, the daily limit value for O₃ (maximum daily 8-hour rolling average) was also exceeded (the first exceedance at the SWRS stations occurred on 14 March and the last one on 8 August).

The situation in individual SWRS regions was balanced – the percentage of days on which the limit values for ozone were exceeded at one of the representative stations varied from 4 to 10 % (Table VI.7).

Synoptic situation during selected smog situations

27–30 January 2014
In the third decade of January, the weather in the Czech Republic was influenced by a cyclone centred over southern Italy, around which warm and moist air flowed into the Czech Republic from the South. This low-pressure area gradually moved over Southeast Europe, and cold Arctic air flowed from the North-East into the Czech Republic between it and anticyclone centered over NW Russia, which brought the coldest days of that winter (25–26 January). At the same time, concentrations of PM₁₀ began to rise. On 27 January a weakening occluded front moved slowly across Bohemia to the North-East, which, however, did not strongly influence the high concentrations of pollutants in the O/K/F-M agglomeration excluding the Třinec region and in the Moravia-Silesia zone, so a smog situation was announced in the area in the early morning hours of Tuesday 28 January. In the following days, the weather in the Czech Republic was influenced by an extensive low-pressure area over Southwest Europe. Dispersion conditions improved thanks to increasing southern air flow, which caused a decrease of concentrations below the threshold value and the withdrawal of smog the situation.

10–12 June 2014
A smog situation was announced in the O/K/F-M agglomeration due to high concentrations of ozone in afternoon hours of Tuesday 10 June. At this time, a high-pressure area stayed over Central Europe, and very warm air flowed into the Czech Republic from the South-West. Sunny weather with the highest daytime temperatures reaching 30–35 °C prevailed in the country. In the afternoon of Wednesday 11 June, a smog situation was announced in the Prague agglomeration. On the same day, a waving cold front passed in afternoon to evening hours across the Czech Republic from the North-West, which brought a pronounced temperature drop and large amounts of cloud with showers and thunderstorms. After the front, a ridge of high pressure expanded over the country from the West, and colder air began to flow in from the North-West along its leading edge. The smog situation in the Prague agglomeration was canceled in evening hours of Wednesday 11 June, and in the O/K/F-M agglomeration it was also canceled in early hours of Thursday 12 June (Fig. VI.6).

2–8 December 2014
Average 24-hour concentrations of PM₁₀ in the Třinec region exceeded the informative threshold value already on Tuesday 2 December, and the regulatory threshold value was exceeded the next day in the O/K/F-M agglomeration excluding the Třinec region, in the Třinec region and in the Moravia-Silesia zone, and the informative threshold value was exceeded in the Central Moravia zone. During this period, the weather in the Czech Republic was affected by an extensive cyclone over the western and central Mediterranean, around which, especially in upper layers of the atmosphere, warmer air flowed into the Czech Republics from the South-East. Consequently, an isotherm to temperature inversion, including a near-ground inversion, formed at the height of 2 km, especially during the night from 3 to 4 December and the night from 4 to 5 December. Only on these days were the legal conditions for announcing a smog situation or issuing a regulatory notice fulfilled (growing trend of 12-hour averages of PM₁₀ in the last 6 hours at half of the stations). During Saturday 6 December, a high pressure belt accompanied by a calming of the wind formed over Central Europe. In the afternoon of the same day, a regulatory notice was issued for the Moravia-Silesia zone excluding the O/K/F-M agglomeration and the Třinec region. The smog situations were canceled on Monday 8 December after a cold front passed the Czech Republic (Fig. VI.7).

Tab. VI.1 The rules for the announcement and cancelling of smog situations and regulations (alerts)

Tab. VI.2 Smog situations and regulations for PM₁₀ – number and duration, 2014

Tab. VI.3 Smog situations and regulations for PM₁₀ – dates and times of announcement, 2014

Tab. VI.4 Concentrations of PM₁₀ (number of days with the exceedance of the limit value/threshold value and the maximum concentrations), 2014

Tab. VI.5 Smog situations and alerts for O₃ – number and duration, 2014

Tab. VI.6 Smog situations and alerts for O₃ – dates and times of announcement, 2014

Tab. VI.7 Concentrations of O₃ (number of days with the exceedance of the limit value/threshold value and the maximum concentrations), 2014

Fig. VI.1 SWRS areas and representative stations for PM₁₀