## 2 Air Quality Monitoring in Terms of Particulate Matter
### Types of Monitoring Stations  
The classification of measurement stations in relation to specific criteria is of great importance in air quality management [12]. Within the European Union, the most important legal acts in this area are the Council Decision of 27 January 1997 establishing a reciprocal exchange of information and data from networks and individual stations measuring ambient air pollution within the Member States known as 97/101/EC Decision together with Commission Implementing Decision 2011/850/EC, containing executive provisions on the reciprocal information exchange system and reports on ambient air quality. The primary division of measurement stations into particular types is based on the influence of the dominant emission source and therefore it can be distinguished into [60; 61]:  
* Traffic stations--pollutants concentrations are influenced mainly by emissions from neighbouring communication routes;
* Industrial stations--pollutants concentrations are influenced predominantly by emissions from a neighbouring single industrial source or industrial area with more sources;
* Background stations--pollutants concentrations are representative of the average exposure of the general population (or vegetation and natural ecosystems) in the area covered by the assessment.  
Among background stations, the following subgroups should be distinguished [60]:  
* Urban and suburban background stations;
* Rural stations:
* Near-city background stations;
* Regional stations;
* Remote stations.  
Suburban and urban background stations are located within cities or agglomerations and monitor the \"average\" air pollution levels (urban background concentrations) resulting from the transport of pollutants from outside the urban area and from emissions within the city [60]. Such stations are not directly influenced by any dominant emission source, unless this source is characteristic for the considered zone. An important goal of measurements carried out at the urban background stations located in the territory of a given EU Member State is also the possibility to determine the average exposure indicator (AEI) and therefore to set the national exposure reduction target and the exposure concentration obligation [21].  
It should be noted that in Directive 2008/50/EC particular subgroups of rural background stations are in general considered together [21]. As indicated in the Article 8 of the Directive, measurements carried out at rural background stations are crucial from the point of view of a better understanding of the impacts of fine particulate matter and the development of appropriate policies in this area. Generally, the primary objective of the PM\({}_{2.5}\) measurements in rural background stations is to provide reliable information on its background levels (Annex IV of Directive 2008/50/EC). This information is further used to analyse elevated concentration levels in more polluted areas (urban, industrial areas, areas exposed to the impact of road traffic). In addition, the results of measurements carried out at a considered stations could provide information on the possible impact of long-range transport of air pollution on the levels of PM concentrations in the country and on the identification of possible sources of PM-related chemical compounds. More detailed information on the types and criteria to be met by the background stations can be found in, for example, [60; 61; 62].