Analysis of concentrations trends and origins of PM10 in selected European cities

Particulate matter is generated in many natural and anthropogenic processes and, therefore, taking part in chemical reactions and physical processes in the atmosphere could affect human health, climate, and natural environment. The dust, after emission to the atmosphere, remains there in a floating state to form an atmospheric aerosol with different properties – depending on the morphology, the fraction, shape, surface, and chemical composition of the particles. The chemical composition of particulate matter is heterogeneous and depends on the type of emission sources and the time of residence in the atmosphere. The contribution of individual types of sources in the total dust emission is different in European countries. The aim of the study was to analyze the concentrations of PM 10 at urban background and traffic stations in the chosen 17 European cities. For this purpose, the data from the database of the European Environment Agency and Chief Inspectorate of Environmental Protection was used. The annual average concentrations of 10 and daily average concentrations of PM 10 in 2014 will be presented to confirm that in the European cities there is a problem about high 10 concentrations, especially in Poland and other eastern countries. In the case of daily average 10 concentration, the highest concentrations of pollutants in the winter season suggests that for the low air quality in these cities the phenomenon of so- called low-stack-emissions from the municipal sector is responsible.


Introduction
Nowadays the air pollution is a huge problem, especially in the cities. Both, politicians and social organizations try to fight with the air pollution in many different ways (for example legal norms, an environmental education etc.). Air pollution is any substance which changes normal composition of the air. The air pollution can have a different origin (natural or anthropogenic), a different physical state (gas, solid or aerosols), a different chemical compositions, a various residence time in the air and even a different ability to long-term transport. Also, some of air pollutants can react with other substances in the air to a new form, sometimes to more dangerous pollution [7]. Particulate matter, also known as dust or aerosols affect human health, environment and climate causing large economic losses [2, 5-7, 11, 13, 14, 16, 19, 20]. Some particulates occur naturally (primary PM), originating from volcanic eruptions, deserts, dust storms, trees, living vegetation, grassland or forest natural fires, and sea spray. Also particulate matter can be produced in the atmosphere through chemical reactions of gaseous precursors (secondary PM). There is a lot of sources of dust emission. The main anthropogenic sources, which are predominant in urban areas, are production processes and fossil fuels combustions (in vehicles, power plants and industrial processes). Metallurgical, energy, chemistry and mining industry are one of the biggest sources of their emission. Also, transport is the important to source of emission (tire and brake and road wear). Domestic heating for households plays the important role in air pollution in Poland [1,7,10,12,18].
Europe has a serious problem with the air pollution, especially a particulate matter pollution. Generally, the worst situation is in big cities. According to the data of the European air-quality database in 2014 PM 10 concentrations continued to be above the UE Limit Value in the large part of Europe [4,20]. Monitoring stations with measured concentrations of PM 10 above daily limit value were situated in 21 EU Member States in 2014. About 94% of the cases were observed in urban or suburban areas [7]. Concentration above the PM 10 annual limit value was monitored in 2014 in 4% of all the reporting to EEA stations. 93% of these stations were located in urban areas. According to the WHO guidelines, annual mean PM 10 was exceeded at 55% of the total amount of the stations and in 31 countries. The decrease in concentrations of PM 10 (about 0.6-0.9 μg/m 3 per year) were observed in 75% stations in Europe in 2000-2014 [7].
Trends of changes in particulate matter PM 10 concentrations in selected European cities in 2010-2014 is presented in the paper. The aim of the study is to analyze the concentration and origin of PM 10 measured at the urban traffic and background monitoring stations, in order to identify the main sources of particulate matter emissions in European cities.

Materials and methods
Data from the databases of the European Environment Agency and Chief Inspectorate of Environmental Protection was used for analysis. Poznan, Wroclaw, Warsaw, Cracow, Gdansk, Wien, Brussel, Praha, Berlin, Copenhagen, Barcelona, Helsinki, Paris, London, Budapest, Roma, and Stockholm are the chosen cities. The analysis of the concentration of particulate matter in these places should help to answer, what are the main sources of PM emission -traffic or so-called low-stack emissions (emissions from sources with a height lower than 40 m. The analysis of concentraction in relation to the limit values is based on the measurement at fixed sampling points. Sampling points chosen to analysis are located at two types of sites: urban background and traffic related locations. The AQD [4] sets the data quality objective as a minimum data capture of 90% (valid data out of all possible in a year) for official assesment purposes. For presented analysis the more relaxed coverage criterion of 50% has been used. It allows taking into account more stations without loss of representativeness. It should be noted that the vast majority of data series taken into consideration have completeness in excess of 75%. The analysis covers the period of 2010-2014.
In accordance with the provisions of the AQD and implementing legislation Member States shall report to the EEA provisional data continuously. This includes primarily the results of automatic measurements (so-called up-to-date UTD data), which are thus available to the public on the European Air Quality Portal. The annual series of verified and validated measurement data are delivered to the end of September in the year following the year of measurements performing. They are reported together with information about the assessment system and the results of annual air quality assessment: declarations of compliance with the air quality standards and descriptions of exceedance cases.
European standards for reference measurements of PM 10 and PM 2.5 were concluded in PN-EN 12341: 2014 Ambient air -Standard gravimetric measurement method to determine the concentration of mass fractions PM 10 or PM 2.5 particulate matter [15]. Basing on weight results the concentration of PM is specified [17].

Measurements results analysis and observations on PM 10 concentrations trends through selected European cities
Annual indexes calculated for each selected cities are used in the presented analysis. These indexes have been calculated separately for urban background and traffic stations, as arithmetic averages of the annual mean values from measuring stations of the specific type in subsequent years. Referring the calculated index to the standards set by the European Commission for the annual PM 10 concentration it can be indicated that the limit values has been exceeded nineteen times in 3 of 18 selected cities. All cases of exceedances were observed in Polish cities: 10 times in Cracow (5 times at the traffic station and 5 background stations ), 3 times in Warsaw for a traffic station and 3 times in Wroclaw (once at the background stations and 2 times for the traffic station) (Tab. 1). PM 10 concentrations approaching the specified standards were observed in Paris and Budapest at traffic stations and in other analyzed Polish cities. The highest and the lowest index value was observed in 2010 at the traffic station in Cracow and in 2012 at background station in Helsinki, respectively. These cities differ in terms of climate and culture that influence the quality of the air. In all of the analyzed cities, the higher concentrations of PM 10 were observed for traffic stations, which are generally located in a close vicinity of the streets with high traffic level. It can indicate the dominant influence of transport emissions on air quality in the central parts of the cities, where the traffic stations are often situated. Referring to the average daily value recommended by the WHO (20 μg/m 3 ) it should be noted, that the population of most European cities are exposed to air pollution by PM 10 levels dangerous to health. In 2010-2014, the value of 20 μg/m 3 was not exceeded only 17 times in 6 cities (Helsinki, Stockholm, Gdansk, London, Copenhagen, Paris).
The Institute of Environmental Protection -National Research Institute (IEP-NRI) study shows the general decrease in PM 10 averaged concentrations in Poland since 2010, both of average annual and daily PM 10 concentrations (Fig. 1) [9]. Since 2007, the calculated index of average annual concentration of PM 10 for Polish does not exceed 40 μg/m 3 . The situation in Polish cities is much worse than the PM 10 pollution expressed as a population weighted index calculated for the whole country using the methodology described in [8]. Concentrations in Cracow and Warsaw is about 20 μg/m 3 higher than the average concentration calculated for the whole country. Although the annual average concentrations in the area of Poland remain several years of below standard values, every year the number of permitted days per year with a value greater than 50 μg/m 3 is exceeded. In Poland, air pollution with PM 10 is generally a seasonal problem -exceedances occur mainly in autumn-winter period, hence the annual average value does not exceed the standard. On the other hand, a large number of days with high concentrations of PM 10 in winter badly affects the quality of life. According to the IEP-NRI study in 2012 standard value of the 24-hour concentration was exceeded on at least one station in 21 of the 28 European Union countries. In 2012 the exceedance of the normative value determined on the basis of percentile values of S90,4 from the daily PM 10 concentrations (above 50 μg/m 3 ) was observed at 21.4% of measuring stations in EU countries (including Poland). In Poland, the exceedance was concerned for 71.6% of the stations. In a case of the limit value established for the annual average concentrations of PM 10 , the exceedances occurred at 5.1% in the EU and 24.2% in Polish stations, respectively [3]. temperatures, as in the autumn-winter season are registered (Fig. 2). Referring PM 10 concentrations reported in Poland in the years 2010-2014 there is observed a clear converse relationship between the air temperature and the concentration of PM 10 in the air (e.g. anomaly cold and very cold periods). This is another proof that the particulate matter in the air in Poland is affected by low-stack emission from the municipal sector. Low temperatures force Polish cities inhabitants to heat homes and fuel burning of poor quality coal (it is associated with their economic situation and the low environmental awareness) affects the deterioration of air quality in the urban areas. Moreover, in winter season often a low wind speed, a high atmospheric pressure and temperature inversion situations can favor the occurrence of smog situation. For selected European cities average daily concentrations of PM 10 in 2014 were analyzed in the way to demonstrate the dependence of PM 10 concentrations on the season. The results are presented in the form of a mosaic in Figure 3. Each grid in the figure shows the daily average PM 10 concentration. The value of the annual average PM 10 concentrations and the number of days with a value of more than 50 μg/m 3 during the year was added to the graph. Presented data show that there is a strong seasonal concentrations change in the Polish cities -in autumn-winter season daily average concentrations and number of days with exceedance of 50 μg/m 3 reach the highest values. A city located in the north of Europe (Copenhagen, Helsinki, Stockholm, London) have concentrations of PM 10 at a similar level throughout the year. Additionally, there are low PM 10 concentrations levels -below the European standards. It shows that an influence of the climate of these cities and also the heating system of buildings is quite different than in cities of Central and Eastern Europe. In other analyzed cities (Vienna, Brussels, Prague, Paris, Berlin, Rome, Barcelona) variation in concentrations within a year was also not observed. It can be assumed that the main source of emissions of PM 10 in those parts of Europe is transport. Similar conclusions can be drawn based on the analysis of hourly PM 10 concentrations averaged for every the same hour within the calendar year (Fig. 4). The analysis of data from the selected background stations shows that in the Polish cities the highest daily PM 10 concentrations are observed in the evening and late evening (18.00-23.00) and then again in the morning (6.00-9.00). It is correlated with the rhythm of home heating -residents (especially owners of old central heating) start heating homes after work (in the afternoon) and then repeat this step in the morning. Also, some influence of worse pollution dispersion situations which sometimes occur during the night hours should be taken into consideration. In other selected cities (Paris, Prague, Berlin, Vienna and Brussels) a slight increase in the concentrations of PM 10 in the morning at the time when people are traveling to work was observed.    In 2014 the maximum daily PM 10 concentration in Cracow and Wroclaw was above 200 μg/m 3 (Fig. 5). In Poland, the appropriate services have the obligation to inform the public about the occurrence of health hazards due to high concentrations of PM 10 in a situation of daily mean value above 200 μg/m 3 . The high PM 10 concentrations episodes (above 100 μg/m 3 ) were also observed in Paris, Poznan, Brussels, Rome, Berlin, and Poznan. The intensity of smog situations (height of concentrations) in Poland is often much greater than in other analyzed countries. Even short-term exposure to such high concentrations of PM 10 could pose a serious threat to human health, especially vulnerable groups (children, the elderly, pregnant women and people suffering from lung diseases) [2].

Summary
The analysis of the data shows that European cities face the problem of air pollution by particulate matter (PM). Every year, millions of inhabitants are exposed to oversize PM concentrations, in the case of PM 10 annually states exceedance of the maximum PM concentrations levels established for the protection of human health. Practically, in each of the analyzed cities the average concentration recommended in the WHO Guidelines (20 μg/m 3 ) was exceeded, and there were only a few cities with background pollution below that level. Definitely, the worse situation is observed in central and east-central Europe, where dominates the culture of apartments heated using the coal, often of poor quality. It can also be seen that location, climate, and terrain of the cities have a huge impact on their air quality. EEA data shows that the highest concentration of PM10 in Europe in Poland, Italy, Bulgaria and Slovakia is registered [3]. While the location of the city in the mountain sites affects the deterioration of air quality (Cracow), cities located in well-ventilated terrain, on the shores of seas and boasting a large area of green spaces in their borders have good air quality (Helsinki, Gdansk).