Flags are used for the indication of the concentrations measured at the time when unusual events occurred near the station, or unusual events were detected during the sampling or analysis.

The use of flags was introduced pursuant to the recommendation of the EMEP programme1 and it follows the respective methodology (EMEP 2001). EMEP has established 10 groups of flags, within which the flags are divided into two categories – valid and invalid data, i.e. the measured concentration is marked with a flag. In the subsequent use of the flagged valid data and in ambient air quality evaluation it should be taken into account that the representativeness of measurement results from the respective station is influenced and limited.

The ISKO database introduced the flags in 2010. The flags are used for the concentrations measured at all CHMI manual measuring stations; at the automated CHMI stations only one internal flag has been used so far, and namely “Local influence”. The use of flags ensures higher quality of analysing the episodes of unusual concentrations measured at a particular station. The flags in this yearbook are used for the first time for ambient air quality evaluation in the CR for the year 2013.

Significant influence of the measured valid concentrations may be indicated with two flags according to the EMEP codes (EMEP 2014): flag 652 indicates construction/building activity in the vicinity of the station, flag 199 indicates local influence; it was introduced in CHMI on 1. 1. 2011.

The extent of the influence on the station measurements is individual according to the nature of the particular local influence. As a significant influence upon the annual characteristics is considered in this yearbook the occurrence of the flags in valid data over 2 %, i.e. if the minimum number of the flagged concentrations of the total number of measured concentrations at the station is equal to or greater than 2 %. The list of the influenced measurements with comments by the data provider, or laboratory, is presented in the following table.

Tab. 1 Influenced measuring at CHMI stations in 2013

1EMEP (The European Monitoring and Evaluation Programme, was founded with the aim to provide the member states of the Convention on Long-range Trans-boundary Air Pollution (CLRTAP), signed in 1979, the qualified scientific information on the problems of air pollution caused by various pollutants and on the evaluation of the effects of their presence in the atmosphere on ecosystems and human health.