Levels of lead in atmospheric deposition in a large urban agglomeration in Poland

Abstract

Lead levels in wet and dry deposition were determined within this project. A network of 10 sampling stations was established. The stations were located in areas characterized by heavy traffic volumes, but away from industrial and/or municipal pollution sources. It was assumed, therefore, that lead in the samples collected was coming primarily from automobile emissions. Measurements were carried out over a period of one year. Both rain and snow samples were collected. Lead concentrations in the samples ranged from 0.6 to 141 µg dm⁻³. They depended on street topography, traffic volume, average speed of the vehicles, frequency of traffic congestion and atmospheric conditions. The highest lead levels in deposition were observed during the cold season.

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Aim of investigation

In 1995, emissions of lead to the air in Poland reached 936.6 Mg, out of which 167.4 Mg was caused by automobiles.¹ Since only 18% of lead emissions in Poland come from mobile sources, long-range atmospheric transport might play an important role in deposition not related to such sources. Annual mean lead deposition in Poland was 1482 mg m⁻² in 1994 and 1629 mg m⁻² in 1995. In the city of Gdańsk, the annual emissions were 0.174 Mg (1994), 0.076 Mg (1995) and 0.083 Mg (1996). On the other hand, in the Gdańsk Voivodship (region) the annual deposition was 151 mg m⁻² and 155 mg m⁻² in 1994 and 1995, respectively. Lead deposition in Gdańsk, Sopot and Gdynia is summarized in Table 1.²

Table 1 Lead deposition in Gdańsk, Sopot and Gdynia between 1991 and 1998, evaluation of the natural environment conditions²

City	Annual lead deposition/mg m^−2
	1991	1992	1993	1994	1995	1996	1997	1998
Gdańsk	25.6	37.8	36.4	27.2	32.1	21.4	35.4	36.0
Sopot	35.0	44.8	25.7	14.0	23.3	16.7	28.0	28.0
Gdynia	18.9	35.8	14.6	24.9	16.2	17.7	59.0	16.0

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The major difference between industrial and municipal emissions on the one hand, and automobile emissions on the other, is the height of the emission source above the ground. Sources of automobile emissions are located between several and several tens of cm above the ground. Consequently, dispersion of the pollutants is hindered. The pollutants affect the environment in the close vicinity of the roads, and their impact decreases rapidly with increasing distance from the road. Dispersion of exhaust gases is affected by several factors, including climate conditions (wind direction and velocity, air temperature and humidity, cloud cover, precipitation) and topography (low vs. high buildings, compact vs. dispersed settlement).

The Gdańsk–Sopot–Gdynia Tricity is an urban–industrial agglomeration. It is characterized by a large number of roads and automobiles. During rush hours, the traffic volume on main routes reaches 1000–2000 vehicles h⁻¹. Such intense motorization development causes many problems. Air quality in a city depends among other things on the amount of exhaust gases emitted by motor vehicles. A large fraction of these emissions is removed from the atmosphere by wet and dry deposition. Thus, qualitative and quantitative analysis of atmospheric deposition can be helpful in evaluating the degree of pollution of the urban environment. This paper presents the effect of motor vehicle traffic on the level of lead in wet (rain and snow) and dry deposition in the Tricity.

Description of the experimental procedures

The sampling of rainwater is not a straightforward task. The reliability of the results of final determination is determined to a large extent by proper selection of the sampling site and method. The determination of the level of air pollution attributable to motor vehicles is an equally difficult task, as air pollution at any given location is the sum of pollution from industrial, municipal and mobile sources. The magnitude of the input from any given source varies depending on the location. To determine the pollution caused by motor vehicles, it is desirable that measuring stations be located in such a way that industrial and municipal emissions, as well as inflow of the pollutants from the surrounding areas, are minimized.

Sampling sites

Numerous factors have to be taken into consideration when selecting the site for precipitation sampling. For example, the surrounding buildings should not be situated closer than their height times four, and similar rules apply to the nearby trees. Also, it is undesirable to locate deposition gauges in excessively open areas. Sloping terrain should be avoided, and so should be areas where the ground can be the source of contamination during dry spells.

Proper selection of sampling/sample preparation and storage procedures is equally important. Errors in the determination of precipitation amount are usually related to the effect of the wind. On the other hand, errors in quantitative analysis are typically caused by too long or incorrect sample storage.

Sampling devices used for precipitation collection can have different designs. The simplest deposition gauges are open containers with well-defined opening areas. They are covered with lids whenever not in use. Typical examples include polyethylene bottles or plastic buckets. Samples collected in this way are normally used for typical physico-chemical measurements (pH, colour, conductivity, etc.). Samples collected for certain types of analyses must be preserved immediately after collection using acids or other chemicals. Deposition gauges are placed in pairs, so that at least two parallel determinations can be carried out.

Precipitation samples were collected according to the above guidelines over a period of 12 months (from January to December 1998) at 10 sites in the Tricity. Total atmospheric precipitation, i.e. wet together with dry precipitation (so-called dry sedimentation), was continuously collected and analysed in monthly cycles at each sampling station.

Each site had slightly different characteristics, which helped establish which factors (traffic volume, average velocity, distance from major highways) affected the levels of lead in deposition to the largest extent. Table 2 summarizes the most critical features of the sampling locations.

Table 2 Sampling sites and their detailed characteristics

No.	Sampling site	Characteristic
1	Gdańsk: Jasień, Kuszników Str., 18°64′ E, 54°62′ N	Traffic volume: ca. 1032 vehicles h^−1
2	Gdańsk: Wysoka, gas station at the Tricity ring road, 18°64′ E, 54°39′ N	Traffic volume during rush hours: 1000–2000 vehicles h^−1
3	Gdańsk: Wrzeszcz, intersection of Leczkowa and Wyspiańskiego Str., 18°40′ E, 54°35′ N	Traffic volume during rush hours: ∼750 vehicles h^−1
4	Gdynia: Karwiny, car dealership at the Wielkopolska Str., 18°55′ E, 54°43′ N	Traffic volume during rush hours: 1000–2000 vehicles h^−1
5	Gdańsk: Wrzeszcz, Narutowicza Str.; “Chemistry A” building of the Technical University of Gdańsk, 18°42′ E, 54°35′ N	Traffic volume during rush hours: 1000–2000 vehicles h^−1
6	Gdańsk: Św. Wojciech, Rzeczna Str., 18°63′ E, 54°30′ N	Traffic volume during rush hours: 1000–2000 vehicles h^−1
7	Gdańsk: Wrzeszcz, Słowackiego Str., 18°43′ E, 54°37′ N	Traffic volume during rush hours: ca. 1084 vehicles h^−1
8	Gdańsk: Wrzeszcz, Jaśkowa Dolina Str., 18°40′ E, 54°35′ N	Traffic volume during rush hours 1000–2000 vehicles h^−1
9	Gdańsk: Wrzeszcz, Karłowicza Str., 18°42′ E, 54°39′ N	Traffic volume during rush hours: up to 2000 vehicles h^−1
10	Gdańsk: Orunia, Jedności Robotniczej Str., 18°51′ E, 54°31′ N	Traffic volume during rush hours: 1000–2000 vehicles h^−1

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Deposition samples were collected using deposition gauges consisting of 2.5 L amber glass bottles equipped with grooved glass funnels and mounted in special stands 1.5 m above the ground. They were installed in accordance with the detailed requirements of the Polish Standard (PN-91, C-04642/02: Research on rainwater contamination, Sampling). The amber bottle was covered with aluminum foil.

The gauges were located in unobstructed areas, whenever possible far from tall structures. Similar gauges were used to collect deposition samples from a nature reserve in Rumia in the Gdańsk region,^3,4 Gauges of similarly simple designs were used by Reimann et al.⁵ in 1994 in Russia, Finland and Norway, by Nürnberg et al.⁶ in the years 1980–1982 in Germany and by Asman et al.⁷ in 1980 in Holland. Before the analysis, all samples were filtered through 0.45 µm pore-size filters. The samples were preserved with nitric acid (special purity; delivered by Merck), using 1 cm³ of acid per 1 dm³ of sample, and immediately analysed.⁸

The effect of prolonged exposition of the deposition gauges at ambient temperatures on the stability of the samples was examined in preliminary studies carried out in 1998. Two standard solutions, containing 5 and 50 µg dm⁻³ of lead, were prepared by spiking precipitation samples collected in previous months with appropriate amounts of standards. The solutions were poured into deposition gauges covered with aluminum foil. The first experiment was performed in January (average temperatures: −2 °C during the day and −5 °C during the night). No change in the concentration of the 5 µg dm⁻³ was determined, while the concentration of the other standard changed only by 0.4%. The second experiment was performed in May (average temperatures: 13 °C during the day and 7 °C during the night). The concentration of the 5 µg dm⁻³ standard changed by 0.2%, while that of the 50 µg dm⁻³ standard by 0.5%. No effect of bacteria, algae and fungi on the concentration of Pb in the simulated rain water samples was established. These experiments proved that 30 day exposure of the gauges without significant changes in the amount of lead collected is feasible.

Analysis

The determinations were carried out by electrothermal atomic absorption spectroscopy (ETAAS) using Atomic Absorption Spectrophotometer Model 210 VGP from BUCK Scientific.⁹ Calibration was based on standard solutions. The analytical characteristics of the method, including precision, accuracy and detection limits, are given in Table 3.

Table 3 Analytical protocol

Parameter	Pb
Instrumentation	AAS, BUCK Scientific model 210-VGP
	Graphite furnace, BUCK Scientific model 220-GF
	Auto-sampler, BUCK Scientific model 220-AS
Technique	λ: 283.2 nm; slit: 0.7 nm; current: 20 mA; sample volume: 20 µl; matrix modifier: 1000 ppm Mg(NO3)2 + 1000 ppm (NH4)3PO4 1 ∶ 1 → (1 ∶ 10), volume: 5 µl
	Furnace program: dry, 5.0 s 250 °C; ash, 5.0 s 850 °C; atomize, 2.5 s 1950 °C
Precision (n = 9)/µg dm^−3	0.05
Accuracy/µg dm^−3	0.02
Analytical detection limit/µg dm^−3	0.1

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Results and discussion

Lead was detected and quantified at all locations. In the winter, lead concentrations in the samples varied from 3.3 to 141 µg dm⁻³, depending on the location of the sampling site. The highest levels were observed in samples collected at site no. 4 (car dealership) in February and at site no. 5 (“Chemistry A” building, Technical University of Gdańsk) in December. Lead concentration exceeded 10 µg dm⁻³ in 47% of the samples.

In the spring, lead concentrations varied between 1.2 and 18.7 µg dm⁻³. The highest levels were observed in samples from site no. 1 (Kuszników Street) and site no. 3 (intersection of busy streets) in March. Lead concentration exceeded 10 µg dm⁻³ in only 7% of the samples.

In the summer, lead concentrations varied between 1.4 and 18.5 µg dm⁻³. The highest levels were observed in samples from sites no. 1 and 2 (gas station) in July. Lead concentration exceeded 10 µg dm⁻³ in 23% of the samples.

In the fall, lead concentrations ranged from 0.6 to 44.9 µg dm⁻³. The highest levels were observed in samples from sites no. 1, 3 and 10 (Jedności Robotniczej Str.) in November. Lead concentration exceeded 10 µg dm⁻³ in 33% of the samples.

It should be pointed out that wet deposition depends for obvious reasons on the amount of precipitation. Thus, at least some of the observed variability can probably be attributed to varying amounts of rainfall in different months and/or locations.

Table 4 presents a comparison of lead levels found in this study with literature data for various regions of the world. Data presented in this table indicate that for example in Germany, in large urban agglomerations lead concentrations in 1984 ranged from 7 to 80 µg dm⁻³. This concentration range is very similar to the ranges observed in big Polish cities in the recent years. The only exception in Table 4 is Preston, England, where lead concentration in 1997 was only 0.31 µg dm⁻³, most likely owing to the increased use of unleaded gasoline and to the fact that Preston is a much smaller agglomeration.

Table 4 Levels of lead in precipitation

No.	Location	Pb concentration range/µg dm^−3
a 80 km northeast of Moscow.
1	Germany^6
	Rural	7–19
	Hamburg	15–17
	Frankfurt area	19–24
	Essen	35–48
	Dortmund	28–34
	Stolberg	40–80
	Goslar	42–54
2	The Netherlands: South Holland^10
	Urban	20
	Rural	13
3	Canada^11
	Montreal	1.9–18.6
4	England^12
	Preston	0.31
5	Russia^13
	Chernogolovka,^a rain	19.3
	Chernogolovka, snow	7.2
6	Poland
	Tricity, this study (1998)	0.6–141
	Kraków^14	1.90–7.30
	Wrocław^15	1–47

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Fig. 1 illustrates lead deposition in kg ha⁻¹ (30 day)⁻¹. To compare the data for different months, Fig. 1 presents the results in terms of 30 day deposition. The 30 day values can be directly compared because they all refer to the same time period. The highest lead deposition was observed for samples collected at site no. 4 in February and at sites no. 3, 6 (allotment) and 10 in October.

Fig. 1 Lead deposition at 10 Tricity locations [kg ha⁻¹ (30 day)⁻¹], A, winter; B, spring; C, summer; D, autumn.

The data obtained were also subjected to chemometric analysis, to establish which characteristics of the sampling location affect lead concentration in the precipitation to the largest extent. No correlation was found between the amount of deposition and the distance to the nearest road or wind direction. Fig. 2 presents the correlation between lead levels in precipitation and the percentage of low buildings (no more than three storeys high) among all the buildings in the vicinity of the sampling site. Statistically significant correlation has been found in this case, with lead concentrations lower at locations with higher share of low buildings. This indicates that tall buildings significantly affect lead transport in the air by hindering air movement.

Fig. 2 Relationship between lead concentration levels in the deposition and per cent share of low buildings (less than three storeys high) among all the buildings surrounding the sampling site.

Conclusions

The air pollution in the Tricity is caused mainly by power plants, industry, municipal landfill “Szadółki”, household emissions and automobile vehicles. The location of the sampling sites is crucial when the effect of vehicles on air pollution in large agglomerations is being evaluated. The ten sampling stations were located in Gdańsk and Gdynia in such a manner that they were as far as possible from other pollution sources. Thus, lead in deposition samples collected was assumed to be coming primarily from mobile sources. The following conclusions were drawn from the one year study.

(i) The highest lead concentrations in the samples collected, thus the largest deposition, were observed at sites located next to roads leading to the Tricity ring road, transit routes through the Tricity, and roads leading to major housing estates

(ii) Lead concentration in the precipitation (rain, snow) and deposition of lead caused by precipitation are both related to atmospheric conditions. The highest concentrations were observed in the winter (sites 4 and 5) and in the autumn (sites 1, 3, 6 and 10).

(iii) A statistically significant correlation was found between lead levels in deposition and the height of buildings surrounding the sampling site. On the other hand, there was no correlation to road distance or wind direction.

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