Carbonaceous species in atmospheric aerosols from the Krakow area (Malopolska District): carbonaceous species dry deposition analysis
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Carbonaceous species in atmospheric aerosols from the Krakow area (Malopolska District): carbonaceous species dry deposition analysis
Katarzyna Szramowiat 1
Katarzyna Styszko 1
Magdalena Kistler 0
Anne Kasper-Giebl 0
Janusz Gołaś 1
0 Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemark t 9//164 , Vienna, A-1060 , Austria
1 AGH University of Science and Technology, Faculty of Energy and Fuels, Department of Coal Chemistry and Environmental Sciences , Av. Mick iewicza 30, 30-059 Krak ow
Organic and elemental carbon content in PM10 was studied at three sites in Malopolska District representing the city centre (Krakow), rural/residential (Bialka) and residential/industrial environments (Krakow). The PM10 samples were collected during the winter time study. The highest concentrations of carbonaceous species were observed in Skawina (36.9 μg·m-3 of OC and 9.6 μg·m-3 of EC). The lowest OC and EC concentrations were reported in Krakow (15.2 μg·m-3 and 3.9 μg·m-3, respectively. The highest concentration of carbonaceous species and the highest wind velocities in Skawina influenced the highest values of the dry deposition fluxes. Correlations between OC, EC and chemical constituents and meteorological parameters suggest that a) Krakow was influenced by local emission sources and temperature inversion occurrence; b) Bialka was under the influence of local emission sources and long-range transport of particles; c) Skawina was impacted by local emission sources.
In recent years, scientists have taken a greater interest
in atmospheric aerosols. This is especially due to the
adverse impact of particulate matter on human health and
due to the climate changes caused by aerosols. Unlike the
gases present in the atmosphere, aerosols have a complex
structure, and are composed of a wide range of both
organic and inorganic chemical compounds.
Aerodynamic diameter sizes range from several
nanometres to several micrometres. The chemical
composition is determined depending on the emission
sources and meteorological conditions in the monitored
region . Through parameters such as solar radiation,
temperature and relative humidity, air pollutants undergo
several transformations and chemical reactions.
Secondary pollutants, like ammonia sulphates and
nitrates as well as organic acids, which are the
constituents of the particulate matter, are the products
of gas to particle conversion. These chemicals are the
result of reactions with gas precursors like SO2, NOx,
NH3 or volatile organic compounds . Coarse fraction
particles in aerodynamic diameter from 2.5 to 10 µm, are
constituted mostly of mineral components, like
aluminium silicates, and other metals and non-metals .
The carbonaceous species (organic and elemental carbon)
concentration contributes to 30 – 40 % of the total mass
of the coarse fraction. Elemental carbon (EC) is a primary
pollutant, directly generated during the incomplete
processes of fuel combustion, mainly diesel oil [4,5].
Thus, EC is frequently considered as a tracer for
pollutants emitted from transportation [6,7]. Organic
carbon (OC) is either, as in the case of EC, directly
emitted during combustion processes (creating primary
organic aerosols), or produced during the chemical
reactions with gas precursors in the atmosphere creating
secondary organic aerosols [8,9].
Due to the increasing threat of high concentrations
of particulate matter, the European Commission set
up directives regulating the limits of aerosols in the
atmosphere. Thus, in accordance with the 2008/50/EC
directive, the daily and annual limits for PM10 are equal
to 50 μg/m3 and 40 μg/m3, respectively. Krakow, like
several other cities from the Malopolska District,
is highly threatened by the accumulation of air pollution
mainly because of the topography of the city and the
presence of local emission sources. Krakow is located
in a basin and is surrounded by high buildings, which
block the natural ventilation of the city.
The aim of the study was to measure the PM10
concentration in the air at three different study locations
of the Krakow agglomeration and to determine the
contribution of elemental and organic carbon into the
PM10 mass. The carbonaceous species dry deposition
fluxes were also computed for the purpose of the study.
2 Experimental part
Samples collection of the PM10 fraction was performed
using a low volume sampler equipped with a 1 kW pump,
a flow meter and a PM10 impactor by Digitel®. The air
flow was regulated to the constant value of 1 m3·h-1.
Particulate matter samples were collected on quartz fiber
filters by Pallflex® with a diameter of 47 mm. Prior
to sampling, filters were pre-heated at 550 oC over 5 h
and, afterwards, conditioned at a relative humidity
of 50±5 % at 20±2 oC over 24h. Sampling was carried out
in accordance with regulations PN-EN 1234:1.
In Krakow on weekdays the filters were changed in 24±2
h intervals, while during weekends (Friday, Saturday and
Sunday) the filters remained in samplers for around
70 hours. In Skawina and Bialka, filters were changed
every 24 hours. Sampled filters were conditioned for 24
hours to achieve a constant humidity prior to weighting.
The mass of the particulate matter was obtained as an
average of three following weightings of the filter.
The OHAUS Discovery DV215CD balance with
a accuracy of ±0,01 mg was used for weighting. Detailed
data on measurement locations are presented in Table 1.
PM10 samples were collected at three different
measurement locations in the Malopolska District:
in Krakow, Bialka and Skawina, representing three
different types of the environment: city centre,
rural/residential area and industrial/residential area,
respectively. Krakow is the second-largest city in Poland
by population and is inhabited by ca. 760 thousand
inhabitants. It is located in the north part of the
Filter type applied
Filter changes intervals
The concentration of organic and elemental carbon was
determined using the thermal-optical method for OC/EC
analysis (OC/EC analyzer by Sunset Laboratory Inc.),
developed for atmospheric samples . The Quartz.par
protocol and laser transmittance methods were applied
during measurements. 10 mm circle punches of quartz
fiber filters with dust were analyzed without
pretreatment of samples prior to analysis. The concentration
of TC, OC and EC was automatically calculated on the
base of the flow of the calibration gas (He+CH4, Air
Liquid, Austria). The detection limits of TC, OC and EC
were equal to 0.32 μg·m-3, 0.32 μg·m-3, and 0.01 μg·m-3,
respectively. The repeatability of results was regularly
controlled on the basis of the determination
of carbonaceous species in the solution of sucrose
containing 200 µg of carbon in 20 µl of solution.
The relative standard deviation was equal to 3 %.
Within the presented study the concentration of the
following inorganic ions: Na+, K+, Mg2+, Ca2+, NH4+,
NO3-, Cl-, SO42- was determined using the method
of isocratic ion chromatography. Two 10 mm circle
punches were extracted in 2 ml of deionized water
(MilliQplus 185, Millipore, 18.2 MΩ ) for anions concentration
Malopolska District. Krakow is inconveniently located
in a basin, thus the natural ventilation of the city
is blocked by the surrounding high buildings. As a result,
pollution accumulates over the whole city. In Krakow,
samples of PM10 were collected in the Krowodrza
District, ca. 1 km from the main street characterized by
a high intensity of traffic. Air aspirators were placed on
the roof of a three-story building, at the height of ca. 10
Skawina is a medium-sized city, inhabited by ca.
25 000 inhabitants. The city belongs to the industrial part
of the Krakow agglomeration and is located ca. 15 km
from the Krakow city centre. In Skawina, samplers were
placed on the roof of a one-family house, at the height
of ca. 5 m, in the residential/industrial part of the city.
Bialka, a small village with 2 000 inhabitants,
is located ca. 60 km from Krakow, in the south-east part
of the Malopolska District. Bialka is a typical
rural/residential area, where almost 90% of households
are heated by coal, frequently of a low quality, or by
wood (in the authors’ own estimation). Samplers were
placed in a garden at the height of 2 m, near the main
determination and in 3 ml of 12 nM methanesulfonic acid
(MSA) for cations concentration determination.
The extraction was carried out for 20 min in
an ultrasonication bath. The DX-3000 (Thermo
Scientific) ion chromatograph equipped with
ionexchange column (anions: Ion Pac AS17A, mobile phase:
1.8 mM Na2CO3 + 1.7 mM NaHCO3; cations: Ion Pac
CS12A, mobile phase: 12 mM MSA) was used in the
study. After electrochemical suppression of eluent,
analyte concentration was determined using the
conductivity detector. Calibration of the method was
based on the determination of the concentration
of analytes in previously prepared external standard
solutions (Merck). Detection limits (obtained multiplying
the standard deviation calculated for blank solutions by
a constant factor of 3.0) were equal to: 0.1 μg·m-3 for Na+
and Cl- and 0.01 μg·m-3 for the rest of the ions.
2.3 Meteorological data
The meteorological data (air temperature, wind speed,
wind direction, humidity and precipitation volume)
of atmospheric conditions in Krakow were downloaded
from the online platform (http://meteo.ftj.agh.edu.pl/)
where the results of the meteorological measurements are
directly transferred from the Vaisala WXT520 automatic
meteorological station. The station was placed on the roof
of the building where the samples were collected.
The meteorological data in Bialka and Skawina were
downloaded from the online platforms
www.meteoprog.pl and www.freemeteo.com. Table 2
includes the meteorological data recorded during the
study periods. In order to compute the backward
trajectory of air masses, the HYSPLIT (Hybrid
SingleParticle Lagrangian Integrated Trajectory) model was
used: (http://ready.arl.noaa.gov/HYSPLIT_traj.php ).
The backward trajectories for the heating season
sampling periods for Krakow, Bialka and Skawina were
calculated basing on the following parameters: height
of computation – 20, 500 and 1500 m a.s.l.; trajectory
duration – 72 h.
3 Results and discussion
3.1 PM10 concentrations at measuring locations
Average concentrations of chemical constituents of PM10
obtained within analytical measurements of particulate
matter samples from Krakow, Bialka and Skawina are
summarized in Table 2. The daily accepted value
of PM10 (50 µg·m-3) was exceeded several times during
all study periods in Krakow (8 exceedances) and Skawina
(7 exceedances), whereas in Bialka extremely high
concentrations of PM10 were reported for the whole
study period resulting in the average value of PM10 equal
to 87.4 µg·m-3 and ranged from 60.4 to 111.6 µg·m-3.
The mean concentration of PM10 in Krakow was
accounted for 60.3 µg·m-3 ranging between 36.5 and
128.4 µg·m-3. Occurrence of PM10 particles in Skawina
was reported on the average level of 62.8 µg·m-3 ranging
between 30.1 and 117.1 µg·m-3 (Table 2).
Figure 1 presents the variations of the PM10
concentration measured for Krakow, Bialka and Skawina
during the study periods against the relative humidity and
ambient temperature. In these plots the episodes of high
concentration of PM10 (> 100 µg·m-3) may be noticeable:
on Feb 11th, 18th and 27th in Krakow, on Mar 3rd, 10th, 13th
and 16th in Bialka, on Dec 29th and 30th and Jan 5th, 6th
and 9th in Skawina. For each sampling period the aerosol
prehistory was profiled by conducting 72-hours air
masses backward trajectories at 24 h intervals at 20, 500
and 1500 m a.s.l (Figure 2). These backward trajectories
enabled to identify the source of origin of aerosols during
the above mentioned episodes of PM10 high
concentrations. PM10 concentration in Krakow
significantly increased on Feb 11th and Feb 18th and
reached the maximum values equal to 100,0 and 128,4
87.4 (60.4 – 111.6) 62.8 (30.1 – 117.1)
4.1 (1.5 – 9.9) 9.6 (5.2 – 15.7)
20.8 (7.4 – 31.8) 36.9 (13.2 – 74.8)
0.9 (0.1 – 2.2) 3.7 (< LOD – 9.2)
2.2 (1.3 – 4.3) 2.3 (< LOD – 4.2)
7.6 (3.3 – 16.0) 3.1 (0.02 – 6.5)
0.3 (0.1 – 0.9) 0.4 (0.2 – 0.7)
3.4 (1.8 – 6.2) 3.5 (2.0 – 5.8)
0.4 (0.1 – 0.8) 0.6 (0.3 – 1.3)
0.01 (< LOD – 0.06) 0.03 (0.01 – 0.10)
0.05 (< LOD – 0.6) 0.2 (0.1 – 0.3)
0.05 (0.02 – 0.1) 0.2 (0.1 – 0.5)
6.4 (2.8 – 10.9) 4.0 (0.8 – 6.7)
-0.3 (-6.4 – 5.9) 2.3 (-5.0 – 7.0)
84 (56 – 99) 94 (80 – 100)
1.4 (0 – 3.1) 5.3 (1.0 – 14.0)
µg·m-3, respectively. These values were reported when
Krakow was under the influence of air masses moving
from the southeast direction. As the local wind direction
on these days was similar to the air mass advection
(Figure 1), the origin of PM10 is influence by local
sources. The backward trajectories computed for Feb 11th
and Feb 18th showed that air masses moved very low,
below the 500 m a.s.l., what together with low humidity
(76 %), temperature (0.4 oC) and wind speed (1.7 m·s-1)
may point to occurrence of the temperature inversion.
For most of the study period in Krakow the air masses
trajectories moved on the height lower than 500 m a.s.l.
with exemptions of Feb 8th, 13th and 24th. Krakow was
then under the influence of west (Feb 8th and 13th) and
southeast (Feb 24th) air masses advection (Figure 2).
These masses carried the middle-polluted by aerosols
ambient air resulting in the PM10 concentrations on these
days equal to: 44.3, 64.9 and 42.6 µg·m-3. Similar
relations were reported for Skawina when on Dec 31st
2013, Jan 4th and 7th 2014 the PM10 concentration was
accounted for 43.9, 54.8 and 70.4 µg·m-3. On these day
Skawina was under the influence of long-range air
masses which moved at the height of 1000 m a.s.l.
Therefore, the long-range transport of aerosols should be
considered, beyond the local sources, as the second
source of particulate matter in Krakow and Skawina.
Especially that in Skawina the wind speed obtained up to
14 m·s-1. On the other hand in Krakow the highest
concentrations of nitrates and sulfates (3.6 µg·m-3 and 6.3
µg·m-3, respectively) were reported. This is especially
seen in Krakow where the highest concentrations
of nitrates and sulfates (3.6 µg·m-3 and 6.3 µg·m-3,
respectively) were reported. Strong correlations between
ions (NO3-/SO42- = 0.67 and NO3-/NH4+ = 0.81, Table 3),
additionally proves the origination of aerosols from the
secondary sources. In Bialka the augmented
concentrations of PM10 which occurred actually during
the whole study period were probably the result
of prevailing meteorological conditions. Low temperature
foster the accumulation and condensation of particles
suspended in the atmosphere. The wind velocity in Bialka
was as low as in Krakow. As a consequence
the pollutants could not be well dispersed.
3.2 Organic and elemental carbon in PM10
The contribution of the total carbonaceous species (TC)
into the PM10 mass was accounted to 32 % in Krakow,
28 % in Bialka and 74 % in Skawina reaching the mean
values of the TC concentration equal to 19.1±10.6,
24.9±10.6 and 46.5±20.4 µg·m-3, respectively.
The highest contribution of carbonaceous species was
observed in Skawina. However, this was affected by the
presence of a specific emission source: in Skawina,
samplers were placed near a factory which usually uses
organic oils for manufacturing processes.
The evaporation of these high temperature organic oils
resulted in the increased contribution of carbonaceous
species. According to the Didyk et al, 2000 study, the
concentration of the TC concentration in highly polluted
urbanized areas is suspected to be at the level of 85
µg·m-3, as it was investigated in Santiago (Chile) .
Significantly lower values were noted in the United
Kingdom: 6.4±4.6 µg·m-3 at the Bristol Road Site,
5.6±3.2 µg·m-3 at the Birmingham city center site and
4.6±3.5 µg·m-3 at the Churchill Pumping Station site.
However, the TC fraction contributed in 24 % at the
Bristol Road Site, in 23 % at the Birmingham city center
site, and in 24 % at the Churchill Pumping Station site
. Gdynia, in turns, is characterized by 5.5 µg·m-3
of TC fraction and 29 % of its contribution into the PM10
mass . Unlike i.e. in South Pole, where the TC
concentration was accounted for 0,0015 µg·m-3 .
Krakow, Bialka and Skawina are more closed to the TC
concentrations reported in Santiago. Moreover, the TC
concentrations reported in three measuring locations were
greater by six orders of magnitude than this one measured
in South Pole.
The mean concentration of elemental carbon was
noted on the level of 3.9±2.8 µg·m-3 in Krakow, 4.1±3.1
µg·m-3 in Bialka and 9.6±3.3 µg·m-3 in Skawina (Table
2), contributing averagely in 6 %, 5 % and 18 %,
respectively, into the PM10 mass fraction. The EC-to-TC
ratio, which performs the origin of carbonaceous species
from anthropogenic sources as the EC is a primary
pollutant , was accounted for 0.19 in Krakow, 0.15
in Bialka and 0.23 in Skawina. The higher the ratio is, the
stronger the environment is impacted by the local
emission sources. The maximum value of the EC/TC was
observed on Feb 2nd in Krakow (0.32), on Mar 4th
in Bialka (0.26) and Jan 5th in Skawina (0.54). These days
were under the influence of the air masses moving on low
heights (~100 m a.s.l.) (Figure 2). The directions of air
masses were similar to wind directions reported for
measuring locations (Figure 1) what points out to the
local sources as incomplete combustion of either diesel
oil combustion (Krakow, Skawina) or fossil fuels
combustion (Skawina, Bialka). In turns, the minimum
values of the EC/TC was observed on Feb 13th in Krakow
(0.11), on Mar 13th in Bialka (0.08) and on Jan 7th-8th
in Skawina (0.13). On these days, the air masses moved
on the high altitudes (above 1000 m a.s.l) carrying the EC
absorbed on the particulates surface. Because EC has
a residence time of 6 days it could be transported
hundreds or thousands kilometers from its source
of origin .
While transporting the particulates over the lands, the
organic compounds could be transformed undergoing
photochemical processes or gas-to-particles conversion
 resulting in the increased contribution of organic
carbon into the total carbon fraction: 81 % in Krakow,
92 % in Bialka and 87 % in Skawina on Feb 2nd, Mar 13th
and Jan 7th-8th, respectively. The mean concentration
of the organic carbon was equal to 15.2±8.0 µg·m-3
in Krakow, 20.8±8.3 µg·m-3 in Bialka and 36.9±19.1
µg·m-3 in Skawina ranging between 7.3 and 35.0 µg·m-3,
7.4 and 31.8 µg·m-3, 13.2 and 74.8 µg·m-3, respectively
(Table 2). Significant correlation between organic carbon
and PM10 was observed for Krakow (0.74) and Skawina
(0.98) pointing out that OC originated from the same
source as PM10 (Table 3). Therefore, in Skawina the
highest concentrations of Cl- and K+ (3.7 µg·m-3 and 0.6
µg·m-3, respectively, Table 2) suggested that, beyond the
manufacturing processes near the study location, aerosols
have an origin in coal and biomass combustion. In Bialka
the occurrence of aerosols was probably influenced by
the presence of several emission sources: a. biomass
combustion as the Spearman’s rang correlation
coefficient for OC/K+ and EC/K+ reached the high values
of 0.94 and 0.89, respectively; potassium ions are mainly
emitted during the biomass combustion ; b. coal
combustion as EC was correlated with Cl-  in 66 %
and with Na+  in 73 % . In Krakow, besides the coal
combustion, the ambient pollution was affected during
the study period by photochemical processes leading
to creation of secondary aerosols. This is confirmed by
significant correlation between OC and NO3- (0.52) and
NH4+ (0.53). Nitrate ions are created during the secondary
reactions with the gas precursor NOx in the atmosphere
. Moreover, nitrates are emitted from Diesel engine
exhausts and during combustion processes, mainly for
houses-heating purposes. In winter time the phenomenon
is especially noticeable as nitrate ions exhibit a stronger
association to ammonium ions in urban areas than in rural
regions . In Krakow and Bialka the significant
correlation between organic and elemental carbon was
reported suggesting the common source of origin.
The existence of different sources and processes
generating various proportions of carbon is reflected by
highly variable OC/EC ratios [7,21]. In this study, the
mean OC-to-EC ratio was accounted for 4.6 (2.2 – 7.8)
in Krakow, 6.4 (2.8 – 10.9) in Bialka and 4.0 (0.8 – 6.7)
in Skawina. Accordingly with considerations presented
by Sillanpaa et al. 2005, a low OC/EC ratio can be
associated with fresh traffic aerosol (2.2 and 0.8 for
lightduty gasoline and heavy-duty diesel vehicles,
respectively), whereas residential heating (wood
combustion 4.15 and natural gas home appliances 12.7),
forest fires (14.5) and dust from paved roads (13.1) show
remarkably higher ratios . Obtained OC/EC ratios for
coarse particles in winter time points out that
on measurement stations carbonaceous constituents had
a complex origin .
3.3 The flux of carbonaceous species dry deposition
Atmospheric aerosols emitted to the atmosphere undergo
various processes like transboundary transport,
degradation or deposition on the ground. The deposition
of particles is a very important process for atmosphere
self-cleaning, which, in turn, influences aquatic
environment pollution levels [24,25]. The average OC
and EC dry deposition flux was accounted for 2.0±0.7
and 0.5±0.3 mg∙m-2∙d-1, respectively in Krakow, 2.6±1.9
and 0.6±0.5 mg∙m-2∙d-1, respectively in Bialka, 13.3±10.6
and 3.7±2.9 mg∙m-2∙d-1, respectively in Skawina.
The values of the dry deposition fluxes of carbonaceous
species were calculated according to the formulas
presented in the previous paper of Styszko et al, 2015
. The values of EC fluxes were lower by one order
of magnitude than OC fluxes at all measuring locations.
The trend of OC deposition flux reflects the trend of EC
deposition flux. Similarly, maximum and minimum
values of the dry deposition flux reflect the variations
in PM10 concentration. Skawina demonstrates the
highest values of carbonaceous species dry deposition
fluxes and is higher by one order of magnitude than
Krakow and Bialka. In Skawina the widest range of OC
and EC fluxes was observed which ranged from 2.3 to
31.6 mg·m-2·d-1 and from 0.8 to 8.3 mg·m-2·d-1,
respectively. It was undoubtedly caused by the highest
contribution of carbonaceous species into the PM10 mass
fraction and the highest values of wind speed reported for
this study period (Table 2).
Figure 3 presents the daily variations of the OC and
EC dry deposition fluxes in the measuring locations with
the inclusion of the incineration amount. In Bialka no
incineration was reported. After each rainy day
in Krakow and Skawina, i.e. Feb 22nd – 25th or Jan 4th –
8th, the OC and EC dry deposition fluxes decreased.
On these days when rain occurred, the particles were
removed through the wet deposition. This is confirmed
by the Spearman’s rang correlation coefficients computed
for OC and EC deposition fluxes and relative humidity
(Table 3). The strongest correlation was observed
in Krakow (IOC) and Skawina (IEC). The higher the
relative humidity is, the lower contribution of the dry
deposition into the particulates removal processes. Białka
and Skawina additionally performed the relation between
fluxes and wind velocity: the increase of the wind speed
forces the increase of the dry deposition flux. In Bialka
two significant increases of the carbonaceous species dry
deposition fluxes were reported: on Mar 2nd and Mar 16th.
On these days, Bialka was under the influence of the west
and northwest air masses moving on the low altitudes.
Additionally, low relative humidity and ambient
temperature below 0 oC caused the increase of the
concentration of carbonaceous species. Augmented
values of OC-to-EC ratios (5.3 and 3.4, respectively)
refer to the origin of organic carbon from photochemical
processes. In Skawina, at the beginning of the study
period (Dec 28th to 31st) the increased values of the IOC
were obtained. In this period the ambient temperature
was below 0 oC what was favorable for aggregation
of organic compounds and their absorption onto the
particulates surface. At the end of the study period (Jan
6th to 8th) Skawina was under the influence of long-range
air masses moving from southwest direction. While
transporting the organic species underwent many
processes resulting in creation of secondary organic
The mean concentrations of elemental particulate carbon
ranged from 3.9 µg·m-3 at the city center to 9.6 µg·m-3
at the residential/industrial site. The mean concentrations
of organic particulate carbon ranged from 15.2 µg·m-3
at the city center site and 36.9 µg·m-3 at the
residential/industrial site. The highest correlation between
OC and PM10 was observed at the residential/industrial
area suggesting the origin of both from the same emission
source. The strong correlation between EC and potassium
ions and between EC and sodium and chloride ions
proves the origination of carbonaceous species from
biomass and coal combustion, respectively. This was
especially visible in rural site. City center site was
additionally influenced by long-range air masses carrying
secondary organic aerosols. It was the consequence
of emission from Diesel engines and accumulation
of pollution during the temperature inversion occurrence.
Deposition is the significant process in self-cleaning
of the atmosphere. Low humidity, the lack
of incinerations and high wind velocities favored the
removal of particles through the dry deposition process.
This work was financed by AGH University Grant no
220.127.116.11. The authors acknowledge the financial support
of OeaD and of the Ministry of Science and Higher Education
(Poland) in the frame of project WTZ (Wissenschaftlich–
Technische Zusammenarbeit), No. PL09/2015.
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