V.4 AIR QUALITY INDEX IN TOWNS AND CITIES
The Air Quality Index (AQI) is an indicator providing summary information on air quality at a particular measuring station. Calculation of AQI for 2016 is based on evaluation of hourly concentrations of nitrogen dioxide (NO2), tropospheric ozone1 (O3) and suspended particulate matter (PM10) so as to best characterise air quality in relation to the pollution limit levels for the protection of human health stipulated by the current legislation. The air quality index is divided into six levels (from 1 to 6, where 1 corresponds to the best conditions). The limiting values are derived from the pollution limit values and, for tropospheric ozone, from information and warning threshold values (Tab. V.4.1). AQI was calculated for 23 urban and suburban automated pollution monitoring stations with simultaneous measurement of all three pollutants. AQI was determined separately for each quantity at the given location and the highest of value was included in the presentation. For calculation of the maximum, it was necessary that the hourly concentration values of all three pollutants be valid for the individual hours.
Good and very good air quality (indices 1 and 2) with a frequency greater than 50 % was present at all the selected locations in 2016. The lowest frequencies of indices 1 and 2 were recorded in the O/K/F-M agglomeration at the Karviná (47%), Ostrava-Fifejdy and Ostrava-Radvanice OZO (almost 51%) stations. On the other hand, the highest frequency with very good and good air quality (over 70%) was recorded, similar to last year, at the Plzeň-Bory and Plzeň-Doubravka stations (Plzeň Region).
The air quality was acceptable and satisfactory (indices 3 and 4) with a frequency between 21 and 47%. Frequency above 40% was attained in the Ústí Region at the stations in Ústí nad Labem-city, Most and Ústí nad Labem-Kočkov, in the Central Bohemian Region at Mladá Boleslav, in the Brno agglomeration at the Brno-Lány and Brno-Dětská nemocnice locations, in the O/K/F-M agglomeration at the Ostrava-Fifejdy, Ostrava-Radvanice OZO, Karviná and Třinec2 stations and in the Moravian- Silesian zone at Opava-Kateřinky.
The air quality was bad and very bad (indices 5 and 6) with a frequency between 0 and 6%. At 12 locations, Plzeň-Bory, Plzeň-Lochotín (Plzeň Region), Mladá Boleslav (Central Bohemian Region), České Budějovice, Prachatice (South Bohemian Region), Brno-Tuřany, Brno-Dětská nemocnice (Brno agglomeration), Jihlava (Vysočina Region), Prague- Libuš, Prague-Riegrovy sady, Prague-Kobylisy (Prague agglomeration) and Zlín (Zlín Region), index 6 was never attained. The greatest frequency of over 4% was attained at the Karviná, Ostrava- Radvanice OZO, Ostrava-Fifejdy (O/K/F-M agglomeration) locations; the frequency of indices 5 and 6 varies between 2 and 3% in Třinec, Most, Opava- Kateřinky and Ústí nad Labem-city (a href="png/fV4-1.png" style="text-decoration: none">Fig. V.4.1).
1For analyses outside the summer season (April – September), concentrations of O3 are considered at the level corresponding to the 1st 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).