Air Qual Atmos Health DOI 10.1007/s11869-015-0374-z

Atmospheric VOCs measurement in Nature Reserve Kopački rit, Croatia Elvira Kovač-Andrić 1 & Gregor Arh 2

Received: 4 May 2015 / Accepted: 12 October 2015 # Springer Science+Business Media Dordrecht 2015

Abstract To determine the impact of volatile organic compounds (VOCs) on ozone formation, their identification as well as air concentration assessment is necessary. These were one of the first collections on adsorption tube samples of VOCs in air from the Nature Reserve Kopački rit. The samples were analysed by gas chromatography coupled with flame ionisation detector (FID) and mass selective detector (MSD), and results for the hydrocarbons with two to six carbon atoms are reported. The results show that among the measured concentrations, ethane, propane and n-butane were the highest. Biogenic hydrocarbon isoprene, whose concentrations follow daily cycle of ozone formation during the summer, was also identified and quantified. We used the cluster analysis (CA) to indentify the possible common emission sources among the measured data. The measured data are discussed in relation to the EU guidelines (Directive 2008/112/EC; Directive 2004/42/EC).

Keywords VOCs . Gas chromatography . Mass spectrometry . Cluster analysis (CA)

* Elvira Kovač-Andrić [email protected] 1

Department of Chemistry, University of J. J. Strossmayer, Cara Hadrijana 8/A, 31000 Osijek, Croatia

2

Faculty of Chemistry and Chemical Technology, Aškerčeva 5, 1000 Ljubljana, Slovenia

Introduction Some volatile organic compounds (VOCs) are carcinogenic and can have a negative impact on human health and plant life (Cape 2003; Guo et al. 2004; Lee et al. 2006; Seco et al. 2007; Kampa and Castanas 2008; Zahed et al. 2010; Fann et al. 2009). Furthermore, some of these VOCs also play important roles in stratospheric ozone depletion and the greenhouse effect (Atkinson 2000; Seinfeld 1986). VOCs are widespread in the atmosphere due to their natural origin, i.e. as they are emitted by plants. The presence and distribution of VOCs in the air is a result of several combined processes: e.g. anthropogenic and biogenic sources, different mechanisms of VOCs oxidation and mixing in boundary layer affected by meteorological conditions (Borbon et al. 2004). Anthropogenic and natural volatile hydrocarbons are important in atmospheric photochemical reactions and are subjected to oxidative degradation processes through reactions with hydroxyl radicals and surface ozone (Atkinson and Arey 2003). In order to study the impact of volatile hydrocarbons on ozone formation, it is necessary to identify both and to know their concentrations in the air (Badol et al. 2004). Many studies regarding measurements of tropospheric ozone and some of its precursors were performed in Croatia and Europe e.g. Scheel et al. 1997. However, little work was done in Croatia regarding the importance of VOCs in atmospheric chemistry, i.e. ozone formation. The present study is one the first to measure volatile hydrocarbons in the air of the Nature Reserve Kopački rit (the word Brit^ in Croatian means reed or marshland) (Kovač-Andrić et al. 2006; Kovač-Andrić 2010). The Nature Reserve Kopački rit is located only a few kilometres northeast of the city of Osijek and creates the possibility of atmospheric interactions. Consequently, we used the cluster analysis which has provided two groups of measured VOCs considering their origin. The Nature Reserve

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canals. With the increase of temperature, the abovementioned types of vegetation emit hydrocarbons into the air. Also as a consequence, isoprene is produced protecting the vegetation from thermal damage as well as from acute doses of ozone (Loreto and Velikova 2001).

Experimental

Fig. 1 Location of the monitoring station (marked with a square)

Kopački rit is one of the largest natural marshlands in Europe with an area of almost 240 km2. Since Kopački rit is one of the few natural marshlands in Europe, it is of great importance to preserve it and keep it intact. For this reason, it is recognised by UNESCO who nominated it for the World Heritage List (UNESCO 2001; Ministry of Environmental and Nature Protection 2011). Diverse vegetation in the marsh of Kopački rit contributes to the specific microenvironment. Most areas are covered by white willow, black poplar and oak, while in the water and among marsh vegetation communities, water lens and water lilies can be found. There are also many different types of sedges along the edges of lakes and

Table 1

The rural site Tikveš (coord. 45°40′19″ N, 18°50′59″ E, 82 m a. s. l.) is a part of the Nature Reserve Kopački rit. It is situated in the northeastern part of the Republic of Croatia in mostly lowland areas between the rivers Drava and Danube (monitoring station is presented in Fig. 1). The measurements were performed in a period from the 25th of May until the 29th of September 2008 to get the insight regarding release of volatile hydrocarbons during the growth season. We sampled every eighth day to obtain concentrations of VOCs for each day of the week, and only the last three measurements in September were sampled every third day. Air samples were taken on a certain day each hour between 8 am and 6 pm. Membrane pump, flow controller (Sierra Instruments INC. Model 901 CT) and adsorption tubes were used for sampling of air. Tubes were filled with 150 mg of Tenax, 150 mg of Carbotrap and 150 mg of Carbosieve. Air was pumped in a direction from Tenax to Carbosieve since the strength of adsorbents increases in this direction (for thermal desorption, the direction was reversed). Air was sampled through each sample tube for 20 min with a flow set to 100 mL/min (total volume of sampled air was 2 L). In order to avoid contamination, the air first passed through the metal tubes and then through a flow controller. Sampling tubes were then analysed by gas chromatography (GC) using two instruments: Varian Star 3400 Cx coupled with flame ionisation detector (FID) and Varian star

Average daily mass concentrations of measured VOC’s in Tikveš, Kopački rit in 2008 Average daily mass concentrations (μg m−3)

Ethane Ethene Ethyne Propane Propene n-butane n-Pentane Isoprene n-hexane Benzene

Means

Std.dev

25/05/08

02/06/08

16/06/08

18/06/08

04/07/08

23/09/08

26/09/08

29/09/08

2.55 1.52 0.41 2.99 1.52 2.56 1.99 1.62 1.43 2.70

1.40 0.59 0.51 2.44 0.78 1.55 1.30 0.70 0.62 1.92

1.49 1.32 0.2 1.07 0.78 0.81 0.86 0.62 1.34 0.52

0.52 0.39 0.02 2.97 1.04 1.76 0.64 1.03 1.51 0.85

5.23 2.12 1.71 1.6 0.56 1.5 2.53 2.4 1.88 5.49

3.99 1.08 0.47 2.86 1.76 3.42 4.79 2.37 2.28 3.14

2.77 1.49 0.16 9.23 2.02 2.28 1.12 2.12 0.91 1.93

2.08 1.38 0.32 2.07 1.43 1.22 1.32 2.07 0.55 1.14

2.93 1.97 0.42 1.76 1.02 2.81 1.54 1.11 0.98 1.75

1.66 1.6 0.05 2.23 2.05 3.3 2.16 0.87 2.3 4.08

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ethane ethene ethyne

concentration / µg m

-3

5

4

3

2

1

0 151

153

161

169

185

194

266

269

272

julian day

Fig. 2 Hierarichal dendrogram for the measured VOCs obtained with Ward’s clustering method

3600 Cx coupled with mass selective detector (MSD). Both instruments were equipped with a 10-port VICI valve (Valco Instruments Co. Inc.) and a cold trap. All connecting tubes were made out of stainless steel and were heated to around 100 °C in order to avoid liquefaction of compounds in the instrument (Veber et al. 2001). Sampling tubes were heated to 350 °C, and volatile organic compounds were injected using helium 6.0 carrier gas (Messer Gmbh) into a cold trap, which was cooled with liquid nitrogen to −196 °C. In the next step, the VICI valve was switched, the trap was rapidly heated to 250 °C and VOCs in a gas phase were injected onto a GC column by using helium carrier gas. Two chromatographic columns were used: Chrompack Al 2O3/KCl PLOT and Restek RTX-5MS. The first column was used to separate

Fig. 3 Average hourly values of the mass concentration of ethane, ethene and ethyne measured in Tikveš, Kopački rit

VOCs with lower boiling temperatures and the latter for the ones with higher boiling temperatures. The temperature programme for the Chrompack column was as follows: Tinit = 3 °C (10 min), gradient1 =2 °C/min to 140 °C and gradient2 =20 °C/min to 250 °C (10 min). For the Restek column, the temperature programme was set as follows: Tinit =50 °C (10 min), gradient1 =3 °C/min to 100 °C and gradient2 = 5 °C/min to 200 °C (25 min). Injector temperature for both instruments was set to 250 °C. MSD transfer line was heated to 250 °C, and FID was heated to the same temperature. For quantification of VOC, two gas standards were used: C1–C6 n-Paraffins Fluka 80311 and standard gas mix Restek VOC AB-18475. VOCs were quantified using Beffective carbon number^ concept (Arh et al. 2011). The response factors of FID are equivalent to the Beffective carbon number^ (ECN) (Stenberg et al. 1962). The ECN concept provides good prediction results for a number of carbon atoms present in hydrocarbon. This method is used by many other researches (Scanlon and Willis 1985; Jorgensen et al. 1990). According to the ECN concept, response factors are proportional to the number of carbon atoms. The meteorological data was obtained from the Meteorological Service of Croatia. They collected the meteorological parameters at Klisa, which is located approximately 20 km south of the monitoring site. Since the area of Kopački rit is flat, it was possible to use the gathered meteorological parameters. Meteorological parameters were solar radiation time (Sun, expressed in h) and temperature (t expressed in °C). Ozone has been monitored with a commercial UV photometer Ansyco O341M (Environment SA). The equipment was regularly maintained and calibrated.

ethane ethene isoprene propene n-hexane n-pentane ethyne n-butane benzene propane

1

2

3

4

5

Linkage Distance

6

7

8

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Benzene

Ethane

Propane

Isoprene

Rigi, CH05

0.06–0.021 0.68–3.21 0.04–0.12 0.39–0.89

Waldhof, DE02

0.07–0.16

1.64–3.12 0.48–0.91 0.05–0.26

Peyrusse Vieille, FR13 0.03–0.10 Starina, SK06 0.07–0.41

0.19–2.54 0.33–0.72 0.66–2.61 1.71–3.15 0.76–0.52 0.98–1.32

Košetice, CZ03

0.08–0.19

0.19–2.99 0.39–1.14 0.06–0.29

Tikveš, HR

0.52–5.49

0.52–3.99 1.07–9.23 0.62–2.40

Results and discussions The VOC levels recorded in this study represent one of the first measurements in the marshland area of Kopački Rit Nature Park. This area is located 5 km southeast of the city of Osijek and creates the possibility of atmospheric interactions because of open-landscape regions that allow blowing of winds from all directions. On the other hand, Kopački rit is also a tourist resort which may be the reason why we observed quite high levels of benzene (5 μg/m3; EU guidelines) that points to substantial contribution of traffic exhaust, industry or forest fires to the measured benzene concentrations (during the year, about 30,000 tourists visit Kopački rit). However, the marshland by itself could be a major natural source of biogenic volatile hydrocarbons. Our study represents an interesting example of the mutual influence of urban and rural (wetland) areas, the city of Osijek and the neighbouring Kopački Rit Nature Park. During summer months, the plants emit more hydrocarbons into the atmosphere in comparison to the emission from other anthropogenic emission sources (Guenther et al. 1995; Borbon et al. 2004). Biogenic hydrocarbons are present in plant cells which secrete oil vaporising through the mesophyll and epidermis (Kesselmeier and Staudt 1999). The most common VOCs emitted from plants are isoprene, terpenes, alcohols, carbonyls and esters. There is increasing evidence that biogenic VOCs play an important role in the adaptation of plants to changing climate and have multiple roles in communication and protection of plants against several abiotic and biotic stresses (Holopainen, 2004; Laothawornkitkul et al. 2009; Holopainen, 2011; Hartikainen et al., 2012). In addition to primary anthropogenic and biogenic sources of VOCs, photochemical reactions and meteorological conditions within the boundary layer of the atmosphere also influence their distribution. Daily distribution of hydrocarbons in the air affects their reactions as well as photochemical reactions and meteorological conditions within the boundary layer convection. Studies showed that the concentrations of volatile hydrocarbons are higher during morning hours and achieve the lowest level during midday. Relatively long-lived VOCs of

isoprene ozone benzene

7

6

-3

Station, country code

anthropogenic origin accumulate in the inversion layer during night time and result in even higher levels in the morning hours. Only for hydrocarbons of biogenic origin one has to expect lower levels during morning hours due to their dependence on daytime temperature and light intensity. During the measuring campaign in 2008 at Tikveš, the following compounds were always identified: ethane, ethene, ethyne, propane, propane, n-butane, n-pentane, isoprene, n-hexane and benzene. The measured values of all hydrocarbons are in relation to the EU guidelines (DIRECTIVE 2008/ 112/EC; DIRECTIVE 2004/42/EC), and in accordance with the Croatian Law on Air Quality values, measured data was not exceeded. Table 1 shows all detected compounds and their average daily concentration. The concentrations of unsaturated hydrocarbons are lower than the concentration of saturated hydrocarbons (Fig. 2). Higher concentrations of ethane and propane can be explained by their accumulation in a lower level of the air boundary layer and especially their long residence times (several days) in the atmosphere during night time. Measurements show no major changes in daily concentrations of hydrocarbons except for propane whose daily concentration was significantly higher on the 4th of July. The cause of that high concentration may be that only a small part of propane is lost in reactions with hydroxyl radicals. Reduced concentrations of light hydrocarbons (excluding ethane and propane) during the summer are associated primarily with reduced emissions of biogenic volatile hydrocarbons and favourable conditions for their decomposition (higher insolation and increased concentrations of atmospheric oxidants). The ethane is known as a plant growth hormone naturally produced mostly in autumn, so its high values in spring are quite uncommon. In the last measurements during the month of September, when lower concentration of hydroxyl radicals

concentration / µg m

Table 2 The concentration ranges for each compound of four VOC for five EMEP stations and Tikveš of summer period 2008

5

4

3

2

1

0 151

153

161

169

185

194

266

269

272

julian day

Fig. 4 Average hourly values of the mass concentration of ozone ([O3]= 10−1μg m−3), isoprene and benzene measured in Tikveš, Kopački rit

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are available and weaker, UV radiation causes the prolonged chemical lifetime of VOCs that results in increase of their ambient levels relative to summer period. Cluster analysis (CA) was used to identify the possible common emission sources among the measured VOCs. The hierarchical cluster was performed for concentration data using Ward’s method. Figure 3 shows the results as a dendrogram. The cluster has two overall groups: in the dendrogram, the first group contains ethane, ethene, ethyne, propene, isoprene, n-pentane and n-hexane; the second contains propane, n-butane and benzene. These results indicate that the first group of hydrocarbons originates from biogenic emissions which is consistent with previous studies (Borbon et al. 2004), while propane, n-butane and benzene are associated with combustion processes (Lemieux et al., 2004; Monks et al., 2009). Furthermore, five stations of the European network (Cooperative Programme for Monitoring and Evaluation of Long-Range Transmission of Air Pollutants in Europe, EMEP) were selected for the comparison of some VOCs with the monitoring site in Tikveš. Two of those stations are semiurban (Rigi, located about 11 km east from Lucern and Waldhof, situated 3 km west from city Langenbrügge) and the other three are located in rural area. Observatory Košetice is located in agricultural countryside, Peyrusse Vielle station is located south west of France (it is the most rural area) and Starina is located at National Park Poloniny. The full geographical coordinates can be found on the web (www.nilu.no/projects/ccc/network.html). They are listed in Table 2 together with their data about average summer concentrations of some VOCs of 2008. When comparing Tikveš with other stations (Table 2), VOCs concentration at Tikveš is usually higher. Benzene was chosen as a reference compound based on a number of considerations. Its concentration is much higher at Tikveš compared to the other stations. Since Kopački rit is a natural marshland and tourist resort, the origin of benzene differs from other observed sites. The concentrations of long-lived species ethane and propane are highest in Tikveš. Isoprene has been directly emitted from vegetation during summer-time (Steinbrecher et al. 2009). Their concentrations are higher in Peyruse Vieille and Tikveš. The levels of VOC concentrations in ambient air of Tikveš were found to be highly unusual and require a more detailed systematic investigation over a longer period. Ozone concentrations are highly influenced by temperature because the temperature dependences affect numerous photochemical reactions (Seinfeld 1986). As it is well known (Steinbrecher et al. 2009), the isoprene emission, like ozone, increases with the ambient temperature and solar radiation, resulting in the highest emission at noon. In summer period, higher ozone concentrations coincided with the occurrence of elevated isoprene concentrations which is in accordance with

the mechanisms of its being released from deciduous trees and wetland plants (Loreto and Velikova 2001; Kovač-Andrić 2010; Kovač-Andrić et al. 2013). Isoprene is primarily emitted from deciduous trees: oak, poplar and willow during photosynthesis, and the sedges growing thickly along the lakes and canals in Kopački rit. Isoprene is considered an important antioxidant in plants. Its role is to protect plants from thermal damage and from harmful effects of ozone as well (Loreto and Velikova 2001). Once isoprene is emitted into the atmosphere, it reacts very quickly with hydroxyl radicals to form hydroperoxides, which contribute to the formation of ozone by oxidising nitric oxide back to nitrogen (IV) oxide. Concentrations of isoprene during the day have a similar pace as ozone (Lee and Wang 2006), opposed to benzene, whose concentrations behave differently from those measured for ozone. Highest concentrations of isoprene were found from 10 am to 4 pm which could represent a biogenic emission that depends upon air temperature and insolation (Steinbrecher et al. 2009; Sharkey et al. 1996). Throughout the period, measured concentrations of isoprene increased from May to July when photosynthetic active radiation and temperature are high (overgrowth of vegetation), and after that, concentrations started to decrease (Fig. 4). In rural atmosphere, isoprene has a pronounced seasonal behaviour with higher summer concentrations (Fuentes et al. 2000).

Conclusions One of the first measurements of volatile hydrocarbons in the air of the Nature Reserve Kopački rit, one of the largest natural marshlands in Europe, is presented. The results for the measured VOCs in Tikveš during growing season of 2008 show that the level of VOCs is not alarming in this protected area. The measured concentrations are below the limit values of EU Directive and Croatian law, and so far, there is no negative impact on the vegetation and human health. Biogenic hydrocarbon isoprene, whose concentrations follow daily change of ozone formation during the summer, was also identified and quantified. In the future, the long-term continuous measurement of VOC is needed in order to identify the typical levels of hydrocarbons in the air and gain an insight into their seasonal variations.

Acknowledgments The authors acknowledge the Ministry of Science, Education and Sports of the Republic of Croatia for financial support (grant no. 0098030 and 0982915-2947). Ministry of Sciences and Technology of Republic of Slovenia is gratefully acknowledged as well. The authors would like to thank dr.sc. Glenda Herjavić for the technical support in the laboratory. We also thank the Croatian Meteorological and Hydrological Service for providing us the meteorological data.

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