## 2 Air Quality Monitoring in Terms of Particulate Matter
### Monitoring of PM--European Data  
Within the Europe, the monitoring of PM air pollution is carried out at air quality stations that are a part of a national (e.g., AURN in UK, PAES in France, NEM in Poland) and/or international networks (e.g., WMO's GAW (Global Atmospheric Watch); European AirBase or EMEP) [75]. The data on the PM mass concentration and chemical composition in Europe is collected within the framework of the European Monitoring and Evaluation Programme (EMEP) [76]. It is also reported by the EU member countries to the European Commission and collected in the EEA's open-access database, that is, AirBase [77], which contains information submitted by the participating countries throughout the Europe starting from 2012. Information on air quality monitoring data, including PM concentration and composition, is also supported by the European Air Quality Portal [78]. In addition, Member States also publishes an annual reports on air quality to the provisions of the Directive, which include a summary of exceedances of normative values together with a collective assessment of the effects of such exceedances. Air quality reports within EU countries are published annually by the European Environment Agency and European Topic Centre on Air Pollution and Climate Change Mitigation (ETC/ACM). The most current report, published in 2018, concern the description of the state of air quality in Europe in the years 2000-2016 and presents updated data on air pollutant emissions and concentrations and urban population exposure for 2016 [12]. As indicated within this report, the concentrations of particulate matter continued to exceed the EU limit values and the WHO AQGs in large parts of the Europe (Figure 1). For PM\({}_{2.5}\) values above the annual limit were registered at 5% of the reporting stations in four Member States and four other reporting countries. The highest PM\({}_{2.5}\) annual average concentrations were registered in Poland, Italy, the Balkan countries, Bulgaria and Turkey. The number of sites measuring concentrations and chemical composition of PM\({}_{10}\) and PM\({}_{2.5}\) has been growing evenly over the last decade [58; 79; 80]. Nevertheless, data published both by the EEA and a group of researchers from all over the Europe indicate that the number of sites on which the aerosol was fully characterized is still limited, especially in the southern and eastern parts of Europe; this is particularly true for fine PM fraction (PM\({}_{2.5}\), PM\({}_{1}\)) [4; 17; 57]. Another problem is the inconsistency regarding location criteria and often limited data sets (in many countries less than 5 years of the reporting time) [58]. It should be mentioned that most of the studies on air pollution by fine PM have been associated with urban sites, however people living within rural areas are often exposed to PM\({}_{2.5}\) originating from both natural sources and human activities [32; 81; 82]. Therefore, more research is needed to better understand this problem and to evaluate the contribution of local sources and long-range transport of air pollutants in the concentrations and compositions of particulate matter. According to the data at the end of 2010 [80], the number of air quality monitoring stations at which the chemical composition of PM\({}_{2.5}\) was measured was only 15 but twice as many as in the previous year (8 stations). The chemical composition of PM\({}_{2.5}\) is investigated at only few EMEP monitoring stations (in Austria, Germany, Spain, Italy and in the case of heavy metals--in Norway and Czech Republic). The latest EEA report on air quality in Europe pointed that the PM\({}_{2.5}\) chemical composition (carbonaceous aerosols and water-soluble ions) were reported in many countries, that is,: Austria, Croatia, Cyprus, Denmark, Finland (except EC), Germany, Ireland, Latvia (except EC and OC), Lithuania, Malta, the Netherlands, Poland, Portugal (except NO\({}_{3}\)-), Slovenia, Spain and the United Kingdom.