V.4 AIR QUALITY INDEX IN TOWNS AND CITIES

The Air Quality Index (hereafter AQI) is a measure presenting an overall picture of air quality at a given measuring station. The AQI for the year 2015 has been calculated based on an evaluation of hourly concentrations of nitrogen dioxide (NO₂), ground- level ozone¹ (O₃) and suspended particles (PM₁₀). This evaluation was carried out with the intent to characterize air quality as best as possible in light of limit values for the protection of human health as by the current legislation. The air quality index is divided into six levels, whose threshold values are derived from limit values, and in the case of ground-level ozone, from informative and warning limit values (Tab. V.4.1). For the presentation of the AQI, 25 urban and suburban automated air pollution monitoring stations, concurrently measuring all three pollutants, were selected. The AQI was ascertained separately for each measured value at each location, and only the highest AQI values are included in the presentation. This required hourly values of concentrations of all three pollutants to be in force at each hour.

In 2015, ‘very good’ and ‘good’ air quality (index levels 1 and 2) exceeded the 50 % frequency threshold at almost all presented localities except those in the O/K/F-M agglomeration. The lowest frequency of index levels 1 and 2 was recorded, besides the town of Karviná, at the stations Ostrava-Fifejdy and Ostrava-Radvanice OZO (O/K/F-M agglomeration). Conversely, the highest frequency of index levels 1 and 2 (over 70 %) was recorded at the stations Plzeň-Bory and Plzeň-Doubravka (Pilsen region). ‘Satisfactory’ and ‘compliant’ air quality (index levels 3 and 4) reached frequencies between 22 and 47 %. Frequencies above 40 % were reached at eleven locations: Ústí nad Labem-město, Most, Ústí nad Labem-Kočkov (Ústí nad Labem region), Mladá Boleslav (Central Bohemia), Brno-Lány, Brno-Dětská nemocnice (Brno agglomeration), Ostrava-Fifejdy, Ostrava-Radvanice OZO, Karviná, Třinec² (O/K/F-M agglomeration) and Opava- Kateřinky (Moravian-Silesian zone without the O/K/F-M agglomeration). ‘Bad’ to ‘very bad’ air quality (index levels 5 and 6) reached frequencies between 0 and 6 %. The highest frequency was reached at the stations Karviná, Ostrava-Radvanice OZO, Ostrava-Fifejdy (O/K/F-M agglomeration). By contrast, the sixth level of the index was not reached at all at the localities Plzeň- Bory, Plzeň-Lochotín (Pilsen region), Mladá Boleslav (Central Bohemian region), České Budějovice, Prachatice (South Bohemian region), Brno-Tuřany, Brno-Dětská nemocnice (Brno agglomeration), Jihlava (Vysočina region), Praha-Libuš, Praha- Riegrovy Sady, Praha-Kobylisy (Prague agglomeration) and Zlín (Zlín region). At the remaining localities, the frequency of index levels 5 and 6 varied below 3 % (Fig. V.4.1). Compared to the year 2014, there were no substantial changes in the proportions of the frequencies of individual air quality levels.

Tab. V.4.1 Air quality index based on concentrations of pollutants

Fig. V.4.1 Relative representation of values of the air quality index calculated based on hourly concentrations of NO₂, PM₁₀ and O₃ at urban and suburban automated stations, 2015
 

¹For analyses outside the summer season (April – September), concentrations of O₃ are considered at the level corresponding to the 1^st degree of AQI, i.e. very good air quality. This method does not influence the overall AQI assessment, nor distort the structure of AQI for O₃.

²Values of the AQI were computed by combining data from the stations Třinec-Kosmos (O₃ and PM₁₀) and Třinec-Kanada (NO₂).