Mercury bonds with carbon (OC and EC) in small aerosols (PM1) in the urbanized coastal zone of the Gulf of Gdansk (southern Baltic)

Ecotoxicology and Environmental Safety 157 (2018) 350–357

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Mercury bonds with carbon (OC and EC) in small aerosols (PM1) in the urbanized coastal zone of the Gulf of Gdansk (southern Baltic)

T

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A.U. Lewandowska , M. Bełdowska, A. Witkowska, L. Falkowska, K. Wiśniewska Institute of Oceanography, University of Gdańsk, Av. Piłsudskiego 46, 81-378 Gdynia, Poland

A R T I C LE I N FO

A B S T R A C T

Keywords: PM1 Organic carbon Elemental carbon Mercury Baltic coastal zone

PM1 aerosols were collected at the coastal station in Gdynia between 1st January and 31st December 2012. The main purpose of the study was to determine the variability in concentrations of mercury Hg(p), organic carbon (OC) and elemental carbon (EC) in PM1 aerosols under varying synoptic conditions in heating and non-heating periods. Additionally, sources of origin and bonds of mercury with carbon species were identified. The highest concentrations of Hg(p), OC and EC were found during the heating period. Then all analyzed PM1 components had a common, local origin related to the consumption of fossil fuels for heating purposes under conditions of lower air temperatures and poor dispersion of pollutants. Long periods without precipitation also led to the increase in concentration of all measured PM1 compounds. In heating period mercury correlated well with elemental carbon and primary and secondary organic carbon when air masses were transported from over the land. At that time, the role of transportation was of minor importance. In the non-heating period, the concentration of all analyzed compounds were lower than in the heating period, which could be associated with the reduced influence of combustion processes, higher precipitation and, in the case of mercury, also the evaporation of aerosols at higher air temperatures. However, when air masses were transported from over the sea or from the port/shipyard areas the mercury concentration increased significantly. In the first case higher air humidity, solar radiation and ozone concentration as well as the presence of marine aerosols could further facilitate the conversion of gaseous mercury into particulate mercury and its concentration increase. In the second case Hg(p) could be adsorbed on particles rich in elemental carbon and primary organic carbon emitted from ships.

1. Introduction Mercury is a metal for which the human body does not exhibit any physiological demand, and indeed it is in every form toxic for humans. The mercury in atmospheric aerosols originates primarily from direct emission from anthropogenic sources (i.e. heat and power production, cement production) or is a result of transformations occurring in the atmosphere. The basic reaction of Hg(p) creation is the oxidation of gaseous mercury Hg(0) in the presence of ozone, hydroxyl radicals and hydrogen peroxide (Lin and Pekhonen, 1999; Fang et al., 2001; Xiu et al., 2005). In the coastal atmosphere, the key role in the processes leading to the formation of Hg bound in aerosols is played by Hg(0) reactions with halides (Sommar et al., 1997; Hedgecock and Pirrone, 2001). As a consequence, unreactive gaseous mercury is transformed into reactive gaseous mercury, RGM (RGM=HgCl2 +HgBr2 +HgOBr+ …), which in turn reacts with water vapor and sea salt particles, increasing mercury deposition as Hg(p). Hg(p) has a short lifetime (from a few days to a few weeks) and on a local and regional scale deposits ⁎

quickly back to the ground via dry and wet deposition (Schroeder and Munthe, 1998; Lin and Pekhonen, 1999; Hedgecock and Pirrone, 2001). Depending on meteorological conditions, Hg(p) can be carried over a distance of 500–800 km from the source of emission, and the distance is the greater, the smaller the particle diameter enriched with mercury (Lindberg and Strattyon, 1998; Wängberg et al., 2003; Liu et al., 2007). These short lifetimes classify Hg(p) generally as a regional toxin (Keeler et al., 1995; Lin and Pehkonen, 1999; Rutter et al., 2008). In general atmospheric Hg is more likely to be concentrated on the surfaces of small particles. Measurements done by Wang et al. (2006) in Beijing (China) showed greater accumulation of Hg(p) on particles of less than 1 µm diameter (PM1). Such small particles increase the surface to volume ratio, which may in turn lead to higher adsorption coefficient values. However previous studies curried out in the coastal zone of the Baltic Sea showed higher concentrations of Hg(p) in particles of more than 2 µm in diameter (Bełdowska et al., 2012). It can be the result of different station locations, synoptic conditions during the measurement time as well as aerosol origin source and their basic chemical

Corresponding author. E-mail address: [email protected] (A.U. Lewandowska).

https://doi.org/10.1016/j.ecoenv.2018.03.097 Received 2 October 2017; Received in revised form 29 January 2018; Accepted 31 March 2018 0147-6513/ © 2018 Elsevier Inc. All rights reserved.

Ecotoxicology and Environmental Safety 157 (2018) 350–357

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Fig. 1. Measurement station in Gdynia and surrounding emission sources.

affected by the combustion of fossil fuels in the communal-utility sector and by land transportation. We have also considered the warm season, when the chemical composition of aerosols is shaped by emission and re-emission from the sea surface and by land and sea transportation. In recent years shipping traffic has increased significantly on the Baltic and is projected to continue doing so (http://www.helcom.fi). This requires focused field campaigns and long term monitoring at many coastal or island stations to achieve datasets for global and temporal coverage. Formulated in this way, the tasks are consistent with the SOLAS programme on Ship Plumes: Impacts on atmospheric chemistry, climate and nutrient supply to the oceans and can be used to identify situations when the quantitative impacts of ship emissions on atmospheric photochemistry and climate forcing are most pronounced. We were also interested in determining, if in the urbanized coastal zone of the sea higher concentrations of Hg(p) can resulted by increase of organic carbon (OC) and elemental carbon (EC) concentrations in PM1.

composition. In typical atmospheric conditions, half of the amount of mercury Hg(II) can adsorb on particles which are rich in elemental carbon, as the adsorption coefficient for Hg on soot is high (Seigneur, 1998). The chemical structure of elemental carbon resembles that of graphite and its surface is highly porous with many adsorption sites (Monge et al., 2010). Mercury adsorbed on carbon in such a small particles like PM1 can be inhaled by humans more easily, thereby representing a greater potential health risk (Harrison and Yin, 2000; Fang et al., 2001; Na et al., 2004; Jensen et al., 2005; Highwood and Kinnersley, 2006; Adar and Kaufman, 2007; Berube et al., 2007). An increase in the concentration of PM10 by 10 μg m-3 leads to an increase in the incidence of breathing, food-related and circulatory illnesses and heightens the risk of death up to 2%. If the exposure to high concentrations of PM10 particles is prolonged, the death rate can rise even to 5% (Wilson and Sangler, 1996). However the most serious threat to the human health pose the smallest particles, below 1 µm of diameter. They are deposited in alveoli, where the effectiveness of toxic metals absorption reaches up to 80%. PM1 can also enter circulatory system (Infante and Acosta, 1991). EC in the polluted atmosphere of major cities comes mainly from emissions from diesel engines and is treated as a direct indicator of atmospheric pollution and the intensity of traffic. Another source of elemental carbon in the atmosphere can be sea transport. Because of the cumulative effects, it is an important factor shaping air quality in the vicinity of seaports and their surroundings (Blais et al., 2005; Su et al., 2006; de Wit et al., 2009). Shipping emission is especially dangerous in terms of combustion of heavy oil fuels with high sulfur content and soot emission. This has an impact on marine tropospheric chemistry, ecological and climatic effects (the formation of ozone and aerosols, acidification, the radiative properties of aerosols over the seas and oceans), as well as heightening health risks to people living in harbor cities and coastal regions. Some of the key compounds emitted from international shipping are also volatile organic compounds (VOCs). Their conversion into particles results in the presence of secondary organic carbon in aerosols (Fermi et al., 2006). Primary processes of OC emission are, for example, fossil fuel combustion, unleaded gasoline combustion, biomass burning and agricultural activity (Duan et al., 2004). Primary aerosols containing organic carbon can also be emitted into the atmosphere as plant spores, pollens or soil organic matter. Daily (24 h) sampling of small and coarse atmospheric particles conducted in the coastal zone of the Baltic Sea by Bełdowska et al. (2012) revealed the sea to be a sink for Hg during the winter months and a source of Hg during the summer months. The aim of the present study was to complete the earlier reports with aerosols of submicron sizes (PM1). For this purpose we have taken into account the heating season, when in the Southern Baltic region air pollution is mostly

2. Measurement methods 2.1. Sampling site The sampling station at which aerosol and meteorological measurements were conducted was situated on the roof of the Oceanography Institute, in the center of Gdynia (54°31′N; 18°48′E), at an altitude of 20 m AGL − 3 m above the tree tops. Filters were exchanged automatically every 24 h between 1.01.2012 and 31.12.2012. In September, PM1 and PM2.5 aerosol samples were not collected due to problems with the air suction pump. Gdynia, which spans 135 km2 and numbers about 250 thousands inhabitants, is an urbanized and industrially developed city located directly adjacent to the Baltic Sea shoreline. Although shipyards and harbors constitute the main industries, there are numerous other industrial plants affecting the atmosphere within a radius of 100 km including: cement plants, paper mills, phosphate fertilizer plants, crematoriums, waste incineration plants and chemical plants. The major heat and energy source in the region are Wybrzeze power plant and Local heat production plant, both located to north-west to the measurement station (Fig. 1). Furthermore, Gdynia is a constituent member (together with Gdansk and Sopot) of the so called TriCity- an urban agglomeration with a population of c.a. 1 million, which is bordered by forests and farmland, and is surrounded with small towns and villages where the majority of houses are heated by low-capacity domestic heating units.

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Table 1 Statistical characteristics of meteorological parameters over Gdynia in 2012. Estimator

x x x x x x x x x x x x

Annual ± SD (min-max) January ± SD (min-max) February ± SD (min-max) March ± SD (min-max) April ± SD (min-max) May ± SD (min-max) June ± SD (min-max) July ± SD (min-max) August ± SD (min-max) October ± SD (min-max) November ± SD (min-max) December ± SD (min-max)

T [°C]

7.7 ± 8.3 (−19.5 to 34.5) 1.6 ± 4.7 (−13.4 to 11.9) − 2.2 ± 6.3 (−19.5 to 12.7) 6.2 ± 3.5 (−5.9 to 19.6) 5.4 ± 3.6 (−2.0 to 19.0) 16.0 ± 4.0 (4.9–31.5) 16.0 ± 3.2 (5.8–28.8) 19.4 ± 3.2 (11.1–34.5) 20.7 ± 2.2 (12.0–32.0) 9.9 ± 4.1 (−1.7 to 25.3) 6.5 ± 1.4 (0.0–14.8) − 0.4 ± 3.9 (−12.3 to 10.6)

V10 [m∙s-1]

Rh [%]

58.1 62.5 57.6 52.3 48.1 45.5 50.8 55.1 50.1 62.2 70.9 67.0

± ± ± ± ± ± ± ± ± ± ± ±

12.5 (10.0–90.0) 10.2 (15.0–88.0) 10.6 (15.0–85.0) 10.1 (10.0–90.0) 19.1 (10.0–90.0) 5.9 (10.0–85.0) 10.6 (10.0–86.0) 10.7 (10.0–86.0) 9.4 (10.0–83.0) 8.8 (10.0–89.0) 6.6 (26.0–88.0) 8.7 (23.0–88.0)

3.0 3.7 3.4 3.5 3.0 2.6 2.6 2.5 2.1 2.9 2.9 2.5

± ± ± ± ± ± ± ± ± ± ± ±

1.1 1.4 1.3 1.1 1.0 0.5 0.9 0.6 0.4 0.8 0.7 0.9

(0.0–27.1) (0.0–27.1) (0.0–20.1) (0.0–14.3) (0.0–10.4) (0.0–7.5) (0.0–9.4) (0.0–9.2) (0.0–6.9) (0.0–11.7) (0.0–9.2) (0.0–9.6)

ƩH [mm]

508.6 24.9 10.5 4.5 14.8 9.5 72.1 163.6 76.1 53.4 62.1 17.3

Irradiance* [W m]

Prevailing air mass [%]

2

Land; 68% Sea: Land 50:50% Land; 79% Sea; 69% Sea; 56% Land; 64% Land; 93% Land; 83% Land, 77% Land; 67% Land; 77% Land; 81%

195 72 112 232 280 330 270 282 265 168 70 53

Symbols: x - mean value SD- standard deviation, (min-max)- minimum and maximum value; T- temperature [°C], Rh- relative humidity [%], ƩH- sum of precipitation [mm], V10- the wind speed at 10 m a.s.l. calculated from formula given by Schwarzenbach et al. (1993). * - data from ARMAAG monitoring station (www.armaag.gda.pl), Prevailing air masses (%) were determined on the basis of air mass trajectories analysis for each measurement day (http://www.arl.noaa.gov/ready.html).

analytical error of external calibration averaged 4.5%. Additionally, inter-laboratory comparison with isotopic 13C method on Elemental Analyzer Instruments NC 2500 NC (with Université du Québec a Montréal) was performed. The agreement between the two methods was confirmed by a high Pearson correlation coefficient value for total carbon (r > 0.9). More details can be found in our previous publications (Lewandowska et al., 2010; Lewandowska and Falkowska, 2013; Witkowska and Lewandowska, 2016; Witkowska et al., 2016a, 2016b).

2.2. Sampling of mercury and carbon in PM1 PM1 samples were collected using a FAI (Hydra Dual Sampler) type sampler on 47 mm Pallflex Tissuqartz quartz filters. The temperature and humidity in the sampler were monitored by heating and ventilation of the system. To eliminate potential contamination of samples with mercury, the filters were preheated at 550 °C for a minimum of 8 h before use and then weighed with an accuracy of 10-5g (XA220/X balance, RADWAG) at a temperature of 23 ± 2 °C and a relative humidity of 40 ± 5%. The filter holder was cleaned once a month with 4 M nitric acid. Filters were loaded and unloaded inside a clean bench, with a laminar flow of air filtered with High Efficiency Particulate Air (HEPA) filter. Particle-free gloves were worn at all times. Collected filters were stored at − 20 °C. Once a week a blank was collected by placing a filter in the Hydra Dual Sampler, which was then exposed outdoors in the sampling apparatus, with the pump off, for about 3 min. Following sample collection, the filters were re-weighed and the mass of aerosols in μg per filter surface area was obtained from the weight difference (WMO/GAW, 2003). The final result in μg·m-3 included airflow through the filter during its exposure (2.3 m3·h-1).

2.4. Analysis of mercury Hg(II) in PM1 aerosols Hg content in PM1 was determined via pyrolysis by use of an AMA 254 Advanced Mercury Analyzer (Leco®). This technique used direct combustion in an oxygen-rich environment, the Hg being reduced to Hg (0) and subsequently transferred to its gas phase form, whereupon detection was conducted using conventional amalgamation-thermal desorption-AAS detection (Bełdowska et al., 2012). This technique did not require any sample preparation (e.g. extraction/digestion) which would pose risk of contamination. The analysis of certified reference materials (NIST Standard Reference Material 2584,Trace Elements in Indoor Dust) produced both satisfactory recovery and precision (RSD equal to 3% of the mean). The MLD (Limit of Detection of the Method) calculated as 3 times the standard deviation of the blanks was 1.2 pg m-3 for mercury concentration calculated per air volume (HgPM1-V) and 0.05 pg g−1 for mercury content converted to particle size (HgPM1-M). The error of the method, assuming a 99% confidence interval, was 4.1%. Concentrations reported in this study have been blank-corrected by subtracting the blank value.

2.3. Analysis of organic and elemental carbon (OC and EC) in PM1 aerosols Organic (OC) and elemental carbon (EC) in PM1 aerosols collected in Gdynia were analyzed using a Sunset Laboratory Dual-Optical Carbonaceous Analyzer. The EUSAAR_2 protocol was applied to the analysis owing to the optimal maximum temperature obtained at the end of the first stage, which amounted to 650 °C and ensured that only 2.5 ± 2.4% of elemental carbon was combusted during the first stage of analysis (Cavalli et al., 2010). A rectangular piece of a quartz filter with a surface area of 1.5 cm2 was placed in a quartz oven, where it was dually analyzed. The method's limit of detection (MLD) for 72 blanks was in order of 0.3 μg per 1 cm2 of the filter (a level of 0.02 μg m-3) for both OC and EC, while the analytical error was < 6% for EC and < 10% for OC (with a 99% confidence interval). All carbon analysis results for the environmental samples were reduced by the values for blank samples and took into account air flow through the LVS (2.3 m3 h−1). The blank sample value for OC did not exceed 3.0 μg per 1 cm2 of the filter (0.2 μg m−3), while for elemental carbon it was below the detection limit of the method. Apart from automatic calibration (internal standard – 5.0% methane in equilibrium with analytically pure He), which takes place at the end of the second stage of analysis, after every 10–15 samples, an external standard was analyzed (99% analytically pure sugar solution). The

2.5. Meteorological conditions Meteorological parameters such as wind speed (Vw), relative air humidity (Rh) and air temperature (T) were measured during every period of sampling by the Huger Weather Station on the roof of the Institute of Oceanography building (Table 1). The collected meteorological data were based on a measurement duration of 30 s and results were averaged according to the overall 24-h sampling duration: from 9:00 a.m. to 9:00 a.m. next day (except wind direction). Measurements were carried out at a height of 20 m AGL, so an amendment was made to ascertain the wind speed at 10 m above sea level (V10) (Schwarzenbach et al., 1993):

V10 = 352

10.4⋅uz [m⋅s−1], ln(z ) + 8.1

(1)

353

Symbols: - mean value SD- standard deviation, (min-max)- minimum and maximum value, N- number of samples, < LD- value below the detection limit (1.2 pg m-3); SOC- calculated using the formula (2) determined by Harrison and Yin (2008). *** In the period from 15 August till the end of September no data was collected because the pumps were broken. * - data from ARMAAG monitoring station (www.armaag.gda.pl); ND-no data.

(0.2–29.5) 258 (1.2–9.9) 30 (1.1–28.5) 28 (1.2–18.2) 30 (1.9–13.5) 14 (1.1–5.6) 14 (2.1–6.3) 27 (1.6–6.4) 28 (2.1–6.9) 14*** (0.2–15.2) 25 (0.2–8.0) 25 (1.7–20.2) 28 1.6 2.3 6.9 3.3 3.7 1.4 1.1 1.4 1.1 3.6 2.5 4.6 ± ± ± ± ± ± ± ± ± ± ± ± 4,9 4.6 8.0 4.2 5.7 3.3 4.1 3.6 3.8 4.6 4.4 7.1 (0,4-6.9) 258 (0.6–5.2) 30 (0.5–6.9) 28 (0.4–5.2) 30 (0.5–3.8) 14 (0.5–3.3) 14 (0.5–3.5) 27 (0.5–3.7) 28 (0.4–2.2) 14*** (0.7–4.5) 25 (0.6–5.8) 25 (0.7–6.1) 28 1,1 1.0 1.5 1.0 1.0 0.6 0.6 0.8 0.5 1.2 1.3 1.3 ± ± ± ± ± ± ± ± ± ± ± ± 1.9 2.0 2.4 1.5 1.7 1.7 1.5 1.6 1.5 2.3 2.1 2.4 (0.5–31.3) 259 (1.4–11.6) 30 (1.3–31.3) 28 (1.5–20.4) 30 (2.3–15.0) 14 (1.2–7.6) 14 (2.7–7.7) 27 (1.9–7.8) 28 (2.6–7.7) 14*** (0.5–17.0) 26 (0.5–10.4) 25 (2.0–22.3) 28 4,1 2.6 7.6 3.7 4.1 1.8 1.3 1.6 1.2 4.1 2.9 5.0 ± ± ± ± ± ± ± ± ± ± ± ±

EC [μg m-3] OC [μg m-3]

5.8 5.4 9.0 4.9 6.4 4.4 4.7 4.3 4.5 5.1 5.3 8.2 12.7 ± 16.7 (< LD-146,4) 292 10.7 ± 8.3 (2.6–35.8) 30 18.1 ± 20.5 (1.3–96.5) 28 17.7 ± 15.9 (3.2–66.4) 30 13.2 ± 10.7 (1.0–30.0) 28 2.2 ± 1.0 (< LD −4.3) 29 2.7 ± 4.3 (< LD−21.1) 26 0.6 ± 0.5 (< LD−1.5) 29 1.2 ± 0.8 (< LD−2.4) 14*** 18.0 ± 13.1 (< LD−40.4) 26 ND 32.9 ± 26.4 (7.7–146.3) 27 12.4 (4.5–106.7) 296 11.4 (4.5–54.3) 30 18.1 (12.9–106.7) 28 12.3 (8.0–62.1) 30 11.6 (21.0–71.7) 28 9.7 (18.8–61.2) 29 7.1 (14.8–38.7) 28 7.0 (5.8–29.2) 29 3.9 (12.3–27.2) 14*** 5.6 (7.8–31.9) 26 6.7 (10.5–33.9) 26 15.0 (13.2–70.7) 28

In Gdynia, a total of 296 PM1 samples were collected over the period from January 1st to December 31st, 2012, in which the following were determined: PM1 mass, and the concentrations of OC, EC and Hg(p). The mean concentration of PM1 was 27.4 ± 12.4 μg m-3 (Table 2) and was higher than the EU annual target (25 μg m-3) for particulate matter with aerodynamic diameter under 2.5 µm (PM 2.5) (EEA, 2014). Higher PM1 values were noted during the heating period (I-IV, X-XII- average 28.6 μg m-3) than in non-heating period (V-IXaverage 24.4 μg m-3). The maximum concentration of PM1 occurred in winter (4-5.02.2012) and amounted to 106.7 μg m-3. In Europe, especially in Poland, the ambient particulate matter (PM) still poses a significant air quality problem (EEA, 2014). Even a decrease of PM2.5 concentrations was noted at traffic and industrial sites, an increase at urban and rural background stations still takes place. The largest increase of primary PM concerns commercial, institutional and household fuel combustion (EEA, 2014). Out of the compounds analyzed in PM1 aerosols, organic carbon content had the greatest share, which constituted 22.6% of PM1 mass. Elemental carbon accounted for 7.8% and mercury for 0.1% of total PM1 mass on average. The remaining 69.5% were constituents not analyzed under this study (eg nitrates, sulphates, ammonium ions, etc.). Mean OC concentration in PM1 was 5.8 ± 4.1 μg m-3 and was comparable to the concentrations obtained in PM10 at the same station by Lewandowska and Falkowska (2013) between 2008 and 2009 (8.1 μg m-3). In general organic carbon concentration measured in Gdynia was typical to those noted in small aerosols at other urbanized

± ± ± ± ± ± ± ± ± ± ± ±

3.1. Mercury and carbon (organic and elemental) in PM1 aerosols

27.5 29.6 37.5 26.6 32.7 31.5 29.4 18.8 16.8 20.1 21.7 32.2

3. Results and discussion

Hg(p) [pg m-3]

All statistical analyses and processing of data presented in this manuscript were performed using Statistica v.12 (StatSoft). Concentrations of OC, EC and Hg(p) as well as additional parameters did not exhibit normal distribution. The nonparametric Kruskal-Wallis test for more than two groups of independent variables following nonparametric procedures was used. A level of significance equal to 0.05 was used for all statistical procedures.

PM1 [μg m-3]

2.6. Statistical analysis and additional calculations

Estimator

Table 2 Statistical characteristics of the PM1, organic carbon (OC), elemental carbon (EC), mercury (Hg (p)), and ozone (O3) concentrations in PM1 measured in Gdynia in 2012.

SOC [μg m-3]

Additionally, the aerosol prehistory was profiled by conducting 48-h air-mass backward trajectories at 3 h intervals using the atmospheric HYSPLIT model (Hybrid Single-Particle Lagrangian Integrated Trajectory) (Draxler and Rolph, 2003; Rolph, 2003). HYSPLIT is a complete system for computing simple air parcel trajectories to complex dispersion and deposition simulations (http://www.arl.noaa.gov/ ready.html). Starting heights were set at the collection height (20 m AGL) in order to interpret mercury, organic and elemental carbon concentration in PM1 particles. Heights of 500 m, 1000 m and 1500 m were also used, depending on the boundary layer height at the sampling site for a given period. For every sample, a trajectory including rain amount was also projected. All trajectories were then divided into two types. Aerosols carried to Gdynia from the north-northeast sector were always influenced by the maritime environment while aerosols from other directions were influenced by continental environments (Fig. 1). The way we presented prevailing air masses is described in details in Witkowska et al. (2016a). Based on the trajectory of air masses for each single measurement period, it was possible to establish the dominant direction of advection (from the land - sea) for each month and for the entire year of 2012 (Table 1).

Annual ± SD (min-max) N January ± SD (min-max) N February ± SD (min-max) N March ± SD (min-max) N April ± SD (min-max) N May ± SD (min-max) N June ± SD (min-max) N July ± SD (min-max) N August ± SD (min-max) N October ± SD (min-max) N November ± SD (min-max) N December ± SD (min-max) N

uz- wind speed at the height of measurement z [m·s-1], z- the height at which wind speed was measured [m].

x x x x x x x x x x x x

O3* [μg m-3]

where:

47.9 35.4 44.1 55.4 63.4 67.3 64.2 56.6 54.1 36.1 24.9 25.8

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stations located in Europe (between 5 and 10 μg m-3 for OC) (Lonati et al., 2007; Godec et al., 2012). Average EC concentration in PM1 (1.9 ± 1.1 μg m-3) was comparable to those measured in Gdynia in PM10 between 2008 and 2009 (2.3 μg m-3). At the same time EC values were typical for urbanized regions of Europe such as Zagreb in Croatia (1.1 μg m-3) or Barcelona in Spain (1.8 μg m-3). The lowest EC concentrations are usually noted at stations with low anthropopressure, eg. in boreal Finnish forests (0.1 μg m-3) (Pérez et al., 2008; Godec et al., 2012). Mean concentration of mercury (12.7 ± 16.7 pg m-3) was on a level that was typical for Central Europe (from 5 to 200 pg m-3) (Wängberg et al., 2001, 2003). Year-long (December 2007–December 2008) measurements of mercury concentrations conducted in Gdynia by Bełdowska et al. (2012) in ultrafine particles (collected on filters with pore size of 0.4 µm) showed Hg(p) concentrations one order of magnitude lower (on average 1.3 pg m-3) than those presented in this study. On the contrary, Hg(p) concentration in coarser particles (sampled on filters with pore size of 2 µm) was higher than obtained in PM1 (20 pg m-3). Studies conducted in other parts of Europe indicated similar concentrations of Hg(p) in small aerosol varied from 5 to 200 pg m-3 (Wängberg et al., 2001, 2003).

PM1 originated from a common source, as indicated by a proportional increase in their concentration (OC-EC, r = 0.83). However, in the nonheating period, that relationship was significantly weaker (OC-EC, r = 0.56) than in the heating period (OC-EC, r = 0.86). The average value of OC/EC ratio was equal to 3.2, and was similar during the nonheating (3.0) and heating period (3.2). In general, OC/EC ratio values ranged from 2.5 to 6.0 for nearly 70% of the time, what suggest that the main source of carbon in PM1 over Gdynia in 2012 year was the combustion of fossil fuels (Shen et al., 2010; Styszko et. al, 2015). Poland consumes 77 million tons of coal per year, which makes it the 10th largest coal consumer in the world and the 2nd largest in the EU, after Germany. According to the official Polish Government Energy Policy Strategy 89% of heat in Poland is generated from coal (https://www. worldenergy.org; https://euracoal.eu, 2018). A similar dependence also persists in Gdynia (http://www.infoeko.pomorskie.pl), where a research station is located. The combustion of fossil fuels is here the fundamental source of air pollution, along with transportation (Bełdowska et al., 2014; Lewandowska and Falkowska, 2013; Bełdowska, 2016). Additionally in our region, and in Poland in general, different kinds of garbage, often containing carbon as well as mercury, are burnt in residential heating systems beside coal, because of the lack of any exhaust gas treatment installations (Ćwiklak and Pyta, 2006). There are about 4 million heating systems in Polish homes and flats, of which only 8% can be classified as modern and burning garbage is very common (www.stat.gov.pl, 2013). During non-heating period, the role of transportation in Gdynia increased as the OC/EC ratio was lower than 2.5 for 48% of the time. Then the wind speed was on average 3.0 m s−1, suggesting local to regional pollution origin (Lewandowska and Falkowska, 2013). The current results indicated that during heating period the concentration of all described PM1 compounds increased with the drop in temperature (Tables 1, 2). This can be attributed to the intensively increasing demand for heat at that time. In addition, during winter the atmosphere becomes stagnant and allows pollutants to accumulate close to the earth (Harrison and Yin, 2008). In the heating period, a statistically significant, inversely proportional correlation with the temperature was observed for all PM1 compounds with land advection (Hg(p)-T, r = −0.7; OC-T, r = −0.6; EC-T, r = −0.6; p < 0.05). In the non-heating period, the correlation with temperature was not statistically significant. At that time, the concentration of all analyzed compounds in PM1 was lower (Fig. 2) and for 45% of the time the mercury concentration was below the detection limit of the method (defined as 3 standard deviations of the blank signal and estimated at 1.2 pg m −3). It was a consequence of elimination of the dominant emission source- fossil fuel combustion for heating purposes. In addition in Gdynia in 2012, the sum of precipitation was on average more than two times higher in the non-heating (377.3 mm) than in the heating period (134.1 mm) (Table 1). Although a humid environment, which causes greater evaporation, would have a positive effect on the content of Hg in the atmosphere, precipitation washes out aerosols enriched in Hg effectively (Gratz et al., 2009). Lombard et al. (2011) suggested that smaller particles are much better scavenged in summer than in winter and that more rain scavenges more particles. It can explain Hg(p) concentration decrease in PM1. A decline in mercury concentration during the warm season due to the higher frequency and amount of precipitation has been also recorded over New England by Mao et al. (2008). However, in the second part of the summer, when air temperature decreased and the air masses were transported from over the sea the increase in concentrations of mercury in PM1 collected in Gdynia occurred (Table 2). It could be aided by the adsorption of gaseous mercury on sea salt particles. In the coastal zone of the Gulf of Gdansk sodium chloride is always present in aerosols regardless of the season, the time of day and direction of advection (Nadstazik and Falkowska, 2001). In a humid coastal atmosphere, a reaction between Hg(0) and halides takes place, and as a result unreactive gaseous mercury transforms into a reactive gaseous mercury. RGM in turn reacts

3.2. Variations in mercury and carbon concentrations in the heating and non-heating periods The nonparametric Kruskal-Wallis test for more than two groups of independent variables showed a statistically significant difference in the concentration of all analyzed PM1 compounds between the heating and non-heating seasons of 2012 (p < 0.05). All of the PM1 components analyzed at the coastal station in Gdynia exhibited higher concentrations in the heating season as opposed to the non-heating season (Fig. 2). The heating period was considered to be a period from 1st October to 30th April, while the non-heating season was between 1st May and 31st September. The average mercury concentration in the heating period was 17.5 ± 18.1 pg m-3 and was higher than the annual mean and non-heating period mean (12.7 ± 16.7 pg m-3 and 2.0 ± 2.7 pg m-3, respectively). The same seasonal fluctuations in mercury concentrations in aerosols in the studied area were reported by Bełdowska et al. (2012) for total aerosol fraction (TPM). Similarly as with mercury, the organic and elemental carbon concentration in PM1 aerosols measured in Gdynia in 2012 was higher in the heating months (6.3 ± 4.7 μg m-3 and 2.1 ± 1.3 μg m-3, OC and EC respectively) than in the non-heating months (4.5 ± 1.4 μg m-3 and 1.6 ± 0.6 μg m-3, for OC and EC respectively). Both forms of carbon in

Fig. 2. Statistical characteristic of carbon species (OC and EC) [µg m-3] and particulate mercury (Hg(p)) [pg m-3] concentrations in PM1 during the heating (I-IV and X-XII) and non-heating seasons (V-IX) of 2012 in Gdynia. 354

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with water vapor and sea salt particles. The last of the described reactions leads to an increase in mercury concentration in PM1 (Sommar et al., 1997; Lin and Pehkonen, 1999; Schroeder and Munthe, 1998; Hedgecock and Pirrone, 2001). An important factor for the adsorption of mercury on marine aerosols could be also solar radiation, which was twice as high in the non-heating period than in heating period (287 W m-2 and 141 W m-2, respectively). An increase in radiation entails intensive RGM production and in consequence its reactions with sea salt (Sigler et al., 2009; Bełdowska et al., 2012; Saniewska et al., 2014). Also ozone concentration was higher during the warm months of the year than in the heating period (60.6 μg m-3 and 37.2 μg m-3, respectively). The dominant reaction of aerosol mercury creation is the oxidation of gaseous mercury Hg(0) in the presence of ozone (Wang et al., 1998; Lin and Pekhonen, 1999). 3.3. Influence of air mass origin on Hg(p), EC and OC interaction in PM1 Mercury in PM1 aerosols measured in the coastal zone of Gulf of Gdansk in 2012 had similar sources of origin as elemental and organic carbon. This was confirmed by a statistically significant relationship (Hg(p)-OC, r = 0.68 and Hg(p)-EC, r = 0.57; p < 0.05). The obtained results clearly indicated the role of advection on concentrations values and bonds formed by mercury and carbon compounds. During the heating period, the concentrations of analyzed compounds were higher at land advection, whereas in the non-heating period the tendency was reversed (Fig. 3). The slightly higher OC/EC ratio in PM1 during the non-heating (3.2) than the heating period (3.0) may indicate the significance of secondary organic carbon (SOC) formation during that part of the year (Strader et al., 1999; Vecchi, 2004). In the warm months of the year there could be an additional portion of organic carbon, released into the atmosphere from the sea surface or as a result of land and sea vegetation (spores, pollen, plant remains, microorganisms or organic matter decomposition), present in aerosols (Cerqueira et al., 2010). Oxidizing organic vapors may be a source of low-volatile organic compounds, which condense to form secondary organic carbon (SOC) (Grosjean and Seinfeld, 1989). SOC may make a greater contribution to aerosols than primary organic carbon (OCPRIM). As annual data was obtained for 2012 in Gdynia, it was possible to calculate primary and secondary organic carbon using the method determined by Harrison and Yin (2008):

SOC = OC − EC∙ (OC / EC )min ,

Fig. 3. Statistical characterization of carbon species (OC and EC) [µg m-3] and mercury (Hg(p)) [pg m-3] concentration in PM1 aerosols under maritime and continental advection during a) the heating and b) the non-heating period of 2012.

(2)

p < 0.05), while no bonds of mercury were found with secondary fraction of carbon (Hg(p)-SOC, r = 0.12; p > 0.05). Because EC is also of primary origin this could indicate, that in the warm months of 2012 mercury in aerosols was associated mainly with carbon of primary origin. During non-heating period stationary carbon sources were largely eliminated, and the OC/EC ratio was low (below 2.5) for 48% of the time. It can prove that part of carbon was emitted by transportation. Because during that time the sea advection from over the seaport and shipyard dominated we suggest that mercury in PM1 could be adsorbed on primary origin carbon emitted by ships and port activity. In this way marine transport, although is not a direct source of mercury, is a vector of Hg between atmosphere – sea/land. It is possible also because in the study region concentration of gaseous mercury, which can be adsorbed on carbon, is higher during warm season than in cold months (Marks and Bełdowska, 2001; Bełdowska et al., 2008). On the other hand shipping emission is recognized as an important source of particulate matter and elemental carbon around the world (Wang et al., 2007; Deniz and Durmuþoðlu, 2008; Minguillon et al., 2008). There is no doubt that today the main environmental impacts of shipping include air pollution, particularly in coastal areas (European Commission, 2002; Cofala et al., 2007; Wang et al., 2007). The Baltic Sea is one of the busiest seas in the world in terms of shipping and maritime traffic, and accounts for up to 15% of the world's cargo transportation. Both the number and the size of ships have grown in recent years, especially in

-3

where: OC and EC are daily OC and EC concentrations [µg·m ] and OC/ ECmin is the lowest OC/EC in 2012. The OC/EC ratio value was calculated for each individual sample (Na et al., 2004; Harrison and Yin, 2008). The concentration of OCPRIM was determined based on the difference between total organic carbon (OC) and secondary organic carbon (SOC) (Harrison and Yin, 2008). In PM1 aerosols SOC was predominant, accounting for 85% of OC mass on average (Table 2). Its share did not differ significantly during the heating season (average 84%) compared to the non-heating season (average 85%). However, a more detailed statistical analysis allowed us to establish that in the heating period, mercury bound with organic carbon (Hg(p)-OC; r = 0.69) and elemental carbon (Hg(p)-EC, r = 0.63) only at land advection. In the case of organic carbon, its binding with mercury was statistically significant for both: secondary fraction (Hg(p)-SOC, r = 0.71) and primary fraction (Hg(p)-OCPRIM, r = 0.65). With advection from the sea, no correlation between mercury and carbon was established. In the non-heating season, taking into account all data, no bonds were formed between Hg(p) and organic or elemental carbon (p > 0.05). However when air masses were coming from the sea, a directly proportional and highly significant correlation between mercury and elemental carbon (Hg(p)-EC, r = 0.98) was noted in PM1 aerosols. Correlation between mercury and organic carbon was significant only for primary organic carbon (Hg(p)-OCPRIM, r = 0.98; 355

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respect to oil tankers, and this trend is expected to continue. Forecasts indicate that due to long-term economic growth, especially in the eastern part of the Baltic region, there will be 64% more cargo shipped on the Baltic Sea by 2020. Under a business-as-usual scenario, it is expected that shipping emissions of air pollution in the seas surrounding Europe will increase by 40–50% between the year 2000 and 2020 (http://www.helcom.fi, 2012).

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4. Conclusions The concentration of PM1 in the atmosphere over Gdynia in 2012 was high both in the warm months and in the heating season. Of all the analyzed compounds in aerosols, the proportion of organic carbon was found to be the highest (22.6%). Elemental carbon accounted for 7.8%, and mercury for 0.1% of the total PM1 mass. The concentrations of all the compounds were at a level characteristic of urbanized cities in Central Europe. All of the PM1 components analyzed at the Gdynia coastal station exhibited higher concentrations during the heating period than at other times. In the cold months of the year, the concentrations increased, especially at land advection, low wind speeds and very low air temperatures and precipitations. At that time, the main source of pollutants in PM1 aerosols was the burning of fossil fuels for heating purposes. Transport played a less important role in the formation of high mercury and carbon concentration concentrations. In the non-heating period the concentration of all analyzed compounds decreased and no mercury was found in aerosols for 45% of the study period. The main reason was that the dominant emission source from fossil fuel combustion for heating purposes was eliminated during that time. In addition to above increased precipitation could be responsible for cleaning the air from significant part of pollutants (Saniewska et al., 2014). In the coastal zone of the sea in 2012, OC and EC had a common origin throughout the year, regardless of the season. Mercury bonds with both forms of carbon were determined by the direction of air mass advection. During the heating period, mercury in PM1 aerosols entered into bonds only at land advection. At such times, there was a common source of Hg(p) and elemental carbon and primary and secondary organic carbon from fossil fuel burning. In the non-heating season, the relationship between mercury and primary organic carbon and between mercury and elemental carbon was noted only when humid and halogen-rich marine air masses came in. That was facilitated by high solar radiation and an increase in ozone concentration. No bonds with secondary carbon have been found then. At that time marine transportation and activity in the seaport and shipyard were responsible for higher OC ad EC emission and through the adsorption of reactive gaseous mercury on carbon, led to higher mercury concentration in PM1 over measurement station. In this way marine transport is an important factor in mercury circulation in the coastal zone. Acknowledgements The present study was conducted as part of project no. D/210/130/ 2011, financed by The Regional Fund for Environmental Protection in Gdansk (Poland). References Adar, S.D., Kaufman, J., 2007. Cardiovascular disease and air pollutants: Evaluating and improving epidemiological data implicating traffic exposure. Inhal. Toxicol. 19 (1), 135–149. http://dx.doi.org/10.1080/08958370701496012. Bełdowska, M., 2016. Review of mercury circulation changes in the coastal zone of Southern Baltic Sea. In: Marghany, M. (Ed.), Applied Studies of Coastal and Marine Environments. InTech. http://dx.doi.org/10.5772/61991. Bełdowska, M., Saniewska, D., Falkowska, L., 2014. Factors influencing variability of mercury input to the southern Baltic Sea. Mar. Pollut. Bull. 86, 283–290. http://dx. doi.org/10.1016/j.marpolbul.2014.07.004. Bełdowska, M., Saniewska, D., Falkowska, L., Lewandowska, A., 2012. Mercury in

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