For assessing and evaluating the level of air pollution, the Air Protection Act divides the territory of the Czech Republic into zones and agglomerations. This chapter is concerned with detailed evaluation of the air quality in the agglomerations of Prague, Brno and Ostrava/Karviná/Frýdek-Místek. These are areas in which the air quality is worsened mainly as a result of transport and industrial sources. In addition, these areas have high population densities; thus the fraction of the population that is exposed to above-limit concentrations in these areas is not negligible.
Pollution roses, whose evaluation for selected locations in the individual agglomerations is part of this chapter, are one of the instruments for interpretation of pollutant concentrations measured at AIM stations. Pollution roses evaluate the average concentration measured at stations for a particular wind speed and direction1. In contrast, the weighted pollution rose contains information on the frequency of occurrence of specific situations and evaluates how the contributions measured for a given wind direction and speed contribute to the average concentration measured at the station at the given time. Differences between these two roses can, e.g., draw attention to an important source in the sector from which the wind blows only occasionally and which does not make a substantial contribution to the average annual concentrations.
1 The calculation took into consideration wind speeds of 0.2 m/s or more. Lower speeds were included in the windless category.