Long-term changes of particulate emission in the industrial region of upper Silesia (Poland) and their effect on the acidity of rainwater

The article presents data from ten-year measurements, which prove that the positive effects in particulate emission were accompanied by some adverse effects in the form of acidified rainwater. A distinctive change of rainwater pH in the Silesia Region (Poland) was first recorded in the early 90's. While in 1989, pH of over 55% of the investigated rainwater samples was above 6, in 1997 the average yearly pH was 4.1 and the pH of 20% of the investigated samples was in the range of 3.1-4.0. Seeking the reason for an increased acidity of rainwater, pH values were compared with emission changes of particulate, SO2 and NO2 across the studied area. Emission factors of Ca, Mg, Na and K were determined based on the data of particulate matter emission from cement production processes, coal combustion processes and metallurgy. This allowed comparing the changes of pH rainwater with the area emissions of alkali elements. An analysis of the correlation between pH values and the changes of particulate matter and alkali elements emission as well as SO2 and NO2 emission in the area under study showed that particulate emission followed by SO2 emission had the strongest impact on the modification of rainwater pH, while the impact of NO2 emission was less distinctive. Additionally, an analysis was made to investigate the relation between rainwater pH and the concentration of alkaline ions in rainwater samples. The highest value r = 0.96 was recorded for Mg2+ ions, the lowest i.e. r = 0.54 for Ca2+ ions. This situation can be explained by the fact that calcium compounds are the soluble substances among the investigated metals. Thus, despite the presence of calcium compounds in rainwater samples, a large amount of their portion does not influence rainwater pH.