Elsevier

Journal of Hydrology

Volume 582, March 2020, 124543
Journal of Hydrology

Research papers
17-Year study on the chemical composition of rain, snow and sleet in very dusty air (Krakow, Poland)

https://doi.org/10.1016/j.jhydrol.2020.124543Get rights and content

Highlights

  • Differentiation of 45 chemical constituents of precipitation is estimated.

  • The chemical composition of rain, snow and sleet are analyzed from long-term data.

  • PM10 has a different effect on the chemical composition of rain from that on snow.

  • Very dusty air can prevent a lowering of the pH of precipitation.

  • pH of precipitation depends on effectiveness of chemical weathering of suspended dust.

Abstract

The paper presents the results of long-term (1996–2017) studies of the chemical composition of rain, snow and sleet in one of the cities with the highest concentrations of particulate matter in the air in Europe. The study included measurements of 45 chemical constituents of precipitation as well as its pH and EC. Concentrations of PM10, SO2 and meteorological parameters were also analysed. Differences in Cl and Na concentrations were found depending on the type of precipitation (snow or rain). These differences are most probably caused by anthropogenic factors, however, to a small extent (~18–19%), they are associated with the total variability of the concentrations of these chemical constituents. The differences between the concentrations of the remaining constituents of precipitation analysed are of lesser or negligible importance. The main processes affecting the chemical composition of precipitation are the chemical weathering of suspended dust and the formation of mineral acid aerosols. These processes shape the chemical composition of both rain and snow in a similar manner. The differences between the chemical composition of rain and snow are the result of the concentrations of and mutual relations between selected chemical constituents and precipitation pH. An important factor affecting the pH of precipitation is the effectiveness of the chemical weathering of suspended dust, which may make the precipitation more alkaline. It is very likely that pH-buffering will occur, which can prevent the pH of precipitation from decreasing, especially in cold periods. Long-term observations of variability in the concentrations of the chemical constituents indicate a slight, but rather constant decrease in concentrations of most of the chemical constituents analysed, as well as in the concentrations of PM10 and SO2 in the air in Krakow. The directions of these changes reflect, to a certain extent, the complex transformations of industrial, economic and social conditions in Krakow within that period. The typical ranges of variability of the recorded values of concentrations/measurement values of 22 chemical constituents and the physical characteristics of rain, sleet and snow presented in the paper can be used as reference ranges of these parameters, typical for an area with a significant degree of atmospheric dust pollution.

Introduction

The chemical composition of precipitation is the result of complex, dynamic interactions between cloud formation processes, microphysical processes and a number of chemical reactions in the atmosphere. However, the concentration and origin of suspended dust as well as anthropogenic gaseous atmospheric constituents have a major influence on the chemical composition of precipitation (Seinfeld and Pandis, 2006). Motor vehicles, industry, mineral extraction and broadly defined agriculture constantly emit various chemical substances into the atmosphere (Mayer, 1999, Kuttler and Strassburger, 1999, Allen et al., 2001, Flemming et al., 2005). Due to high traffic volumes and industrialisation, urban areas are responsible for the emission of various types of particulate air pollutants to a greater degree than rural areas (Kim and Shon, 2011, Kim et al., 2012, Sharma et al., 2014). The use of fossil fuels as a power source for industry and internal combustion engines increases the emission of air pollutants such as: SO2, NOx, volatile organic compounds (VOCs) and various aerosols (Sillman, 1999, Atkinson, 2000, Marr and Harley, 2002, Murphy et al., 2007, Teixiera et al., 2008, Wang et al., 2013, Masiol et al., 2014). The combustion of petrol and diesel in vehicle engines results in the formation of particles with aerodynamic diameters ranging from below 0.1 to 2 μm (Lodge et al., 1981, Harrison et al., 1996). As a result, traffic-related aerosols are particularly visible in fine particulate matter. As a result of oxidation of SO2 and NOx contained in the exhaust gases from heating systems and vehicles, high concentrations of SO4 and NO3 can be found in precipitation (Kellman et al., 1982, Stockwell and Calvert, 1983). In densely industrialised areas, this has led to the large-scale occurrence of acid rain and/or photochemical smog (Lickens et al., 1976, Lickens and Butler, 1981, Daum et al., 1984, Low et al., 1991, Wang and Wang, 1995, Lickens et al., 1996, Hadi et al., 1999, Castillo et al., 1983, Galloway et al., 1976). The results from stable sulphur isotopes confirm that SO4 in precipitation primarily originates from high temperature (minimum mean over sampling period 680 °C) combustion of fuels with δ34S signatures ≤4.4‰ (Górka et al., 2017). According to the above-mentioned authors, the stable oxygen isotope composition of sulphates and precipitation water indicates that the contribution of sulphate (generated directly by industrial processes) was <49% during the long-term observation period, with a mean of ~20% during the non-heating and ~40% during the heating periods. Heavy metals are also important contaminants related to industrial processes. Heavy metals emitted in combustion processes are mostly soluble and reactive due to the small size of the transporting particles. Thus, they dissolve readily in the rain, especially under conditions of low pH (Herrera et al., 2009). A significant percentage of the total content of heavy metal particles falls with rain at the location where they were generated as a result of their high relative masses (Nurnberg et al., 1984). Lighter aerosols containing smaller particles of heavy metals, with low precipitation velocity, are easily carried by the wind (Smirnioudi et al., 1998). They remain in the atmosphere until they are removed by various purification processes, including dry and wet deposition (Hamilton-Taylor and Willis, 1990, Yoo et al., 2014). Some of the heavy metals contained in the precipitation are taken up by the plant root systems, and also by the leaf blades, and introduced into the food chain (Chaney et al., 1998). Some of these metals are essential for the proper functioning of living organisms (e.g. Cu and Zn), while others – such as Cd, Pb, As – are dangerous (Caussy et al., 2003, Adamus et al., 2004). Heavy metals introduced into the soil through wet and dry deposition inhibit the growth of local microorganisms, disturbing the processes of decomposition and transformation of organic matter (Hander et al., 2001, Becker et al., 2006). Understanding the mechanisms governing the chemical composition of the atmosphere is important for its short and long-term impact on the ecosystem as a whole and on human health in particular (Steinnea, 1990, Kanellopoulo, 2001, Ostro, 2004, Perera and Emmanuel, 2005, Samoli et al., 2008, Cooper et al., 2010, Apte et al., 2015, Lee et al., 2015). The load of chemical constituents carried by precipitation may have a significant impact on the natural environment, including animals and humans (Bytnerowicz et al., 2005). Studies of the chemical composition of precipitation can provide detailed data on the changes and other characteristics of local and/or regional atmospheric air pollution (Calvo et al., 2010, Budhavant et al., 2011, Cerqueira et al., 2014, Wu et al., 2015). Due to the large spatial and seasonal variability of meteorological conditions, the quantity of pollutants transferred by precipitation varies greatly. This differentiation results from, among other things, differing areas of origin of the pollutants, changing altitude for cloud formation, and the direction of movement of air masses. The dynamics of changes in air pollutant contents close to the Earth's surface (<1.0 km) are high. The average aerosol residence time in the air is one to six days (Stefan et al., 2010). At the same time, it is estimated that in moderate latitudes, rain removes 70–80% of the mass of aerosols from the atmosphere (Falkowska and Lewandowska, 2009). The analysis of the chemical composition of precipitation is used to evaluate and estimate the impact of anthropogenic and natural emission sources on the atmosphere: wet deposition of toxic inorganic compounds, the weathering and dissolution of particulate matter (PM) as well as the long-distance transport of suspended dust. Studies analysing these aspects of the chemical composition of precipitation in urban areas were presented by multiple researchers (e.g. Kanellopoulo, 2001, Hu et al., 2003, Moulia et al., 2005, Song and Gao, 2009, Huang et al., 2010, Abdus-Salam et al., 2014, Mehr et al., 2019).

The aim of this study is to identify dependencies shaping the chemical composition and to determine the sources of origin of the chemical constituents in various types of precipitation (rain, snow, sleet) in Krakow, one of the cities with the highest level of particulate matter air pollution in Europe. The research can help to better understand the complex processes affecting the chemical composition of different types of precipitation and to determine the potential load of chemical compounds introduced into the environment in this manner. It is also important to determine the typical, most frequently occurring ranges of variation in the concentrations of selected chemical constituents and the values of the measurements of the physical characteristics of rain, snow and sleet. Another significant consideration is the analysis of the temporal variability of concentrations of selected constituents of precipitation in order to enable the general directions of changes in the concentrations of these constituents over the 1996–2017 period to be determined. This will provide grounds for an analysis of research results over time and the formulation of predictions regarding the potential directions and dynamics of changes in the recorded concentrations of the chemical constituents and the values of the measurements of the physical characteristics of precipitation.

Krakow is a medium-sized European city (about 770 thousand residents) and a regional transport hub with a well-developed road and rail network. Large industrial plants located directly in Krakow and its immediate vicinity include ArcelorMittal Poland SA (steelworks, roasting or sintering installations) and power plants: EDF Krakow, EC Jaworzno, EC Skawina (CHP plants and other combustion installations). In 2000–2017, the average annual values of PM10 and PM2.5 in the centre of Krakow reached the following ranges, respectively: 56–96 and 38–61 μg·m−3. During this period, average annual concentrations of PM10 >50 μg·m−3 were observed from 132 to 262 days per year. The characteristic feature of the air polluting dust in Krakow is the high content of carbon particles (soot) and very high content of fine particles PM2.5 and very fine particles PM0.1 (Wilczynska-Michalik et al., 2015). This is typical of the aerosols found in urban areas (Buseck and Adachi, 2008). As a rule, the PM2.5 concentration in Krakow is 60–80% of the value of the PM10 concentration (Wilczynska-Michalik et al., 2015). Very dusty air also leads to significant soil contamination. In Krakow, the level of heavy metals in the soils within the city centre is significantly higher than the natural level of these elements in soils (Gąsiorek et al., 2017, Ciarkowska et al., 2019). Air pollution in Krakow shows a clear seasonal variability and reaches its highest levels in the cold period. This is largely due to the heating systems found in most of the buildings in Krakow. Low-calorific coal (<25 kJ), wood, coal waste with a high content of non-flammable dusts and iron sulphides, and in extreme cases even municipal waste are often used as fuel. The occurrence of episodes of high concentrations of air pollutants in Krakow in the cold period may indicate that this phenomenon is similar to the London type of smog, but a significant difference is the relatively low concentration of SO2. The annual average winter SO2 concentrations in the years 2007–2017 did not exceed 20 μg·m−3. Juda-Rezler et al., (2011) indicate that episodes of high concentrations of PM10 in cold periods in the cities of southern Poland (including Krakow) are more strongly associated with local pollutant emissions than in cities in central and northern Poland, where particles from distant sources (long-range transport and regional transport) constitute a more significant element of the PM10 composition.

Dense urban development and its location in a deep river valley, which reduces the possibility of natural ventilation and favours the formation of fogs, have a negative impact on the air conditions in Krakow. According to some authors, the main factor contributing to the high concentrations of particulate matter in Krakow is not usually a sharp increase in emissions (although this may indirectly be related to a decrease in temperature), but a deterioration in conditions conducive to the dispersion of pollutants in the near-ground layer of the atmosphere (Pietras, 2013).

Irrespective of the negative impact on human and animal health, atmospheric pollution also affects inanimate elements of the environment. Long-lasting high concentrations of sulphur compounds, but also of other gaseous constituents and dusts, in the air in Krakow have caused significant damage to the stone elements of many valuable historical structures. The process of destruction of the stone elements was associated primarily with the crystallisation of gypsum and other salts in the pore spaces of rocks, causing so-called salt weathering (Wilczyńska-Michalik, 2004).

Section snippets

Sampling and measurements

The precipitation sampling site is located in the centre of Krakow, within an area populated by blocks of flats (4-storeys) in close proximity (~50 m) to a very busy traffic route (road and tram traffic). The CIEP (Chief Inspectorate for Environmental Protection – data are from the JPOAT 2.0 air quality database) monitoring point for air pollution information is also located in the city centre, approximately 2 km from the precipitation sampling site. It is located in very similar conditions, in

Database

The database contains physical, chemical and meteorological data. Two research sub-periods can be distinguished in the dataset. In the period from 1996-04-03 to 1998-01-31, 57 cases were listed in the database. Then, there was no data until 2002. In addition, in the period from 2002-09-24 to 2017-07-11, 985 cases were listed in the database. The data refers to rain (R), snow (S) and sleet (RS) samples. Physical and chemical analyses include the measurements of 47 parameters. These include pH

The initial analysis and preparation of data

The Kolmogorov-Smirnov (K-S) test was used to analyse the normality of data. The results of the K-S test showed that all the parameters tested were characterised by a distribution different from normal. An attempt was made to normalise the distribution of these parameters using different types of transformations: logarithmic, Fisher and Box-Cox. The best results were achieved for the Box-Cox transformation, however, there are still many parameters with abnormal distributions (Table S1).

Results

The chemical composition of particular types of precipitation is presented in graphic form as Fig. 2.

Table 3 shows the ranges of variability in the recorded concentrations of selected chemical constituents and the measured values of the physical markers of rain, snow and sleet (Table 3). The criteria for selecting the parameters are described in chapter 3.

The results of the analysis of variance (Table S3) indicate that there are significant differences between the mean concentrations or

Chemical composition of precipitation and its range of variation

The Fig. 2 shows general relationships in the chemical composition of particular types of precipitation. Snow and sleet are generally characterised as a population with a lower pH and an increased content of Cl and Na compared to rain. Despite their high variability, the results of the studies are grouped into partially overlapping clusters, which differ in shape. This is particularly true for rain and snow. Therefore, despite the changing conditions shaping the chemical composition of

Conclusions

The research completed permitted a better understanding of the processes shaping the chemical composition of different types of precipitation in one of the most polluted cities in Europe. It was found that the concentrations of chemical constituents differed depending on the type of precipitation. This conclusion applies mainly to rain and snow, and is observed primarily for Na and Cl, but is only to a small extent associated with the total variability in concentrations of these chemical

CRediT authorship contribution statement

Tomasz Kotowski: Conceptualization, Formal analysis, Investigation, Methodology, Software, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing. Jacek Motyka: Conceptualization, Data curation, Investigation, Methodology, Project administration, Resources, Writing - original draft. Wiesław Knap: Data curation, Investigation, Methodology, Resources, Validation. Jarosław Bielewski: Data curation, Investigation, Resources, Software, Writing - original draft.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are very grateful to the Reviewers of our manuscript who offered very insightful, important and constructive comments for improvement of the final version of the manuscript.

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