Long-term trends of pollutant concentrations in selected sites in Silesian Voivodeship

. The assessment of the air pollution quality in selected sites of Silesian Voivodeship was presented in this paper. The evaluation based on the sets of long-term data, recorded by the state air monitoring network. Concentrations of main air pollutants such as PM10, O 3 , CO, SO 2 , NO 2 , NO were considered. The basis for the calculations were 12-year time series of hourly concentrations. Using this data, the monthly averages of pollutant concentrations were calculated. Long-time trends of concentration changes were determined for each pollutant separately. Based on the analysis of trends, risks that may arise in the future were identified.


Introduction
Silesian Voivodeship has the opinion of the most polluted region of Poland. Cities like Zabrze and Rybnik are often mentioned as extremely contaminated places [1]. Long-term measurements of the air monitoring stations allow to answer the question how the air quality has changed in these towns. The aim of the study is to identify the trends of changes in the concentration level of main air pollutants.
Currently in Poland, the state network of air monitoring operates according to the new regulations, which are in line with the European Union legal acts. The present monitoring program started functioning shortly before Poland's accession to the EU [2,3]. In previous years, air monitoring measurements were actually carried out, but on other principles. Therefore, in this examination, 2005 was adopted as the starting point in the analysed time series. 12-year observations should allow to determine the real trends. Designing trends allow to identify the air quality hazards that may emerge in the future.

Methods
Concentrations of basic air pollutants such as: O3, NO, NO2, CO, SO2, PM10, registered in the years 2005-2016 at air monitoring stations in Zabrze and Rybnik, were used in the analysis. Both stations are located in big industrial centers and belong to the type of urban background monitoring sites. The analysed data were received from the Voivodeship Inspectorate of Environmental Protection in Katowice. Using time series of 1hour (instantaneous) concentrations, the monthly mean concentrations were calculated. For each pollutant, 12-year courses of monthly concentrations were determined. Linear trends were adjusted to the courses. Trend lines were determined by the least squares method. Based on the analysis of trends, risks that may arise in the future were identified.

Results
Results of the analysis were shown in figures 1-12. The figures picture long-term courses of monthly concentrations as well as trend lines, for each pollutant and each site separately.

Summary and discussion
Summary of the results was shown in tab. 1. The direction coefficient values of the obtained trend equations were analysed to estimate the direction and strength of the concentrations changes. The strongest changes were observed in the case of SO2, NO2 and CO concentrations. In the both towns those concentrations have been decreasing. Concentrations of PM10 have been decreasing slower. O3 concentrations have been decreasing in Zabrze but in Rybnik they were more stable. Only in the case of NO concentrations, the increasing was observed, however, at low concentration level. According to the European Environment Agency report, in the years 2000-2015 total emissions of air pollutants decreased in EU [4]. Similar trends have been observed in Poland. Since 2000 the following drops of emission has been estimated: 51% for SO2, 25% for CO, 22% for particulates, 14% for NOx [5].
Generally, the changes in pollution levels at stations Zabrze and Rybnik should be considered advantageous for the environment. The rapid fall in SO2, CO and NO2 levels indicates an effective policy of reducing air pollution. Several years ago Poland was classified as a country with exceptionally high SO2 emission. An evident drop of SO2 concentrations indicates that long-term programs for limitation emission of this gas are effective. Moreover, the favourable trends are noticeable in Silesia, the region where coal is mined and burned in large quantities. The increase of NO concentrations with the simultaneous decline of NO2 concentration is not something dangerous. The biggest problem are PM10 concentrations. Although the gradual decrease in concentration can be noted, but still the levels of concentration during heating periods are too high. The reason is low emission from very common domestic installations burning coal waste. It can be assumed that smog episodes resulting from high concentrations of PM10 will continue to occur in many sites in Poland, because government policy is very hesitant in this regard.
Trends observed in Silesian cities coincide with European trends. Europe's air quality is slowly improving, but particulate matter and ground-level ozone continue to cause serious impacts on health [6]. Despite numerous actions to improve the air quality, the following issues still constitute an serious problem in Poland: exceedances of target value for tropospheric ozone during the summer season and exceedances of limit values for particulate matter PM10 and benzo[a]pyrene during the winter season [7].