Comparison of biomass burning tracer concentrations between two winter seasons in Krynica Zdrój

Biomass burning is one source of air pollution that emits soot, smoke, particulate matter, free radicals and other substances, affecting human health, air quality, cloud formation processes and climate change. During biomass burning, organic biomass burning tracers are emitted, such as levoglucosan and its isomers mannosan and galactosan, which are formed at temperatures above 300 °C during cellulose and hemicellulose pyrolysis. The objective of this research is the measurement of biomass burning tracer concentrations in PM10 samples in Krynica during two winter seasons from 01.12.2017 to 31.03.2018 and from 01.12.2018 to 26.03.2019. The average concentrations of organic carbon were 9.48 μg/m3 in the 2017/2018 season and 8.79 μg/m3 in the 2018/2019 season. The average concentration of levoglucosan in the PM10 samples in 2017/2018 was 137 ng/m3, while in 2018/2019, the average concentration reached 245 ng/m3. Levoglucosan was the dominant compound among the determined biomass burning tracers, accounting for 88.6% in 2017/2018 and 72.4% in 2018/2019. The conducted measurements show that the levoglucosan to mannosan ratio was equal to 10.5 and 3.9 in 2017/2018 and 2018/2019, respectively. The biomass smoke organic carbon was approximately 10.6% in 2017/2018 and 20.5% in 2018/2019. These results correspond to the contribution of biomass smoke to organic carbon, which was equal to 14.4% and 28.4% in the 2017/2018 and 2018/2019 seasons, respectively.


Introduction
Biomass burning is a global phenomenon resulting from forest fires and slashes and the burning of forests for agricultural, agricultural waste burning and residential uses. Biomasses, such as straw; wood in the form of pellets; granules or sawdust; and waste, such as scales, can be used as fuel during direct combustion or co-firing. Biomass burning (BB) is a source of air pollution that emits particulate matter, free radicals and other substances, which affect human health, air quality, cloud formation processes and climate change (Schkolnik and Rudich, 2006). In recent years, several organic molecular markers have been widely used in terms of monitoring environmental pollution with biomass burning. During biomass burning, organic biomass burning tracers are emitted, such as levoglucosan (LG) and its isomers mannosan (MN) and galactosan (GA), which form at temperatures above 300°C during cellulose and hemicellulose pyrolysis. These three tracers are most suitable and recognized due to their high abundance and relatively long stability under specific environmental conditions (Fabbri et al. 2009;Zhang et al. 2010;Simoneit et al. 1999;Simoneit 2002). As levoglucosan is the most abundant among all mentioned biomass burning tracers (Schmidl et al. 2008;Simoneit et al. 1999), the relative abundance of LG to MN and GA in atmospheric particulate matter (PM) is affected by the type of biomass burnt (Fabbri et al. 2009;Schmidl et al. 2008). The LG/MN ratio is higher than 50 for a poor quality brown coal, while for softwood and hardwood/grass combustion, it is approximately 5 and 10-20, respectively. The number of grasses is approximately 25 (Fabbri et al. 2009;Schmidl et al. 2008), and the burning of rice straw is 26.6 ). The LG/MN ratio can be used to distinguish wood type burnt, but it makes it difficult to separate emissions from hardwood and crop residual burning (Cheng et al. 2013). The concentration of biomass burning tracers can be determined by different techniques, but the most popular techniques are gas chromatography with mass spectrometry (GC/MS) and high-performance liquid chromatography with pulsed amperometric detection (HPLC/PAD) (Schkolnik and Rudich 2006;Janoszka and Czaplicka 2019). In this research, the concentration of biomass burning tracers was determined by GC/MS.
In Poland, the levels of biomass burning tracers are poorly documented. Consequently, the European Union has funded research on air quality to determine biomass burning tracer concentrations. To address this shortcoming, this report focuses on the following objectives: (i) determination of the level of biomass burning tracer concentrations in PM 10 samples from the health resort Krynica during two winter seasons, 2017/ 2018 and 2018/2019; (ii) determination of individual biomass burning tracer percentages from the total sum of tracers in PM 10 ; (iii) determination of LG/MN and LG/(MN+GA) ratios; and (iv) estimation of organic carbon contribution from biomass burning in the total OC.

Materials and methods
Samples of PM 10 were collected over a 24-h cycle on 47 mm Whatman QMA quartz filters at the measurement station Krynica (health resort φ = 49°24′ 28″, h = 20°57′ 39″, h = 582 m above sea level) from 01.12.2017 to 31.03.2018 (118 samples) and from 01.12.2018 to 26.03.2019 (112 samples). Samples were collected in accordance with the methodology described previously (Klejnowski et al. 2017) with the use of a low flow sampler with separating head PM 10 Atmoservice PNS3D15/LVS3d, with a stabilized flow of 2.3 m 3 /h. Blank samples were checked before every month (8 in total).
The concentrations of biomass burning tracers were determined based on the method described by Poore (2002). Levoglucosan, mannosan and galactosan were determined by placing a sample of PM 10 collected on a quartz filter (one half of the 47-mm filter) in a 4-ml dark glass vial. The following were added to the sample: 2 ml of pyridine (POCH) as a solvent and 50 μl of a mixture of N,O-bis(trimethylsilyl)trifluoro-acetamide and trimethylchlorosilane (BSTFA: TMCS, 99: 1, Supelco) as a derivatizing agent. The vial was shaken for 1 min after closure and placed in an oven at 40°C for 30 min. The extracts (1 ml) were analysed after filtration through a syringe filter (0.22 μm) using a Shimadzu GC-2010 gas chromatograph coupled with a mass spectrometry detector equipped with an HP-5MS column (30 m, 0.25 mm, and 0.25 μm). The limit of detection (LOD) was equal to 0.25 ng/m 3 for LG, 0.11 ng/m 3 for MN and 0.12 ng/ m 3 for GA. The limit of quantification (LOQ) was equal to 0.76, 0.34 and 0.35 ng/m 3 for LG, MN and GA, respectively. Method precision expressed as a relative standard deviation was equal to 19%, and recovery was 95%. Pure levoglucosan was purchased from Sigma-Aldrich, Germany. Mannosan and galactosan were obtained from LGC, Germany. The validation parameters are presented in Table 1.
The analysis of organic carbon (OC) was performed with the use of a thermal-optical organic and elemental carbon analyser, Sunset Laboratory Inc., using the EUSAAR_2 protocol, which was developed as a proposed standard method for European measurement stations under the European Supersites for Atmospheric Aerosol Research project (EUSAAR project, CEN/TR 16243, 2011). For each real sample batch/series, the blank samples were analysed to verify the presence of OC. Based on the results of the 1.0 cm 2 pieces from the 25 blank samples, the LOQ was calculated as 0.94 μgC/ cm 2 for OC. Repeatability was estimated from 25 independent measurements of the same sample under the same measuring conditions (slice of quartz filter with a glucose standard solution of concentration 4 μgC/ μL). Repeatability determined that the relative standard deviation for OC was 1.6%.

Results and discussion
The mass concentrations of the analysed chemical species, biomass burning tracers, PM 10 and OC for health resort Krynica are summarized in Tables 2 and 3 and Figs. 1, 2 and 3.
The average mass concentration of PM 10 was 28.4 μg/m 3 in the 2017/2018 season and 24.6 μg/m 3 in the 2018/2019 season. These results correspond to the results from Gothenburg and Umeå with a PM 10 concentration of 21 μg/ m 3 (Ferm and Sjöberg 2015) and a regional background of approximately 20 μg/m 3 , as determined by Forsberg et al. (2005) in Sweden, e.g., Trelleborg and Malmö. A similar annual average of 24.5 μg/m 3 was reported by Monteiro et al. (2018) in Porto. The results are higher than those of Riccione, Italy, with a concentration of 8 μg/m 3 (Vassura et al. 2014), but lower than those of Cracov and Brzezina, Poland, with a mean value of approximately 100 μg/m 3 (Samek et al. 2013). The average temperature during the winter season in 2017/ 2018 was − 2.2°C, and in the season 2018/2019, it was − 1.4°C.
The mean biomass burning tracer concentrations from Krynica in the two winter seasons of 2017/2018 and 2018/ 2019 were 155 and 338 ng/m 3 , respectively. The average concentrations of the three biomass burning tracers in Europe are very diverse, e.g., 379 ng/m 3 in rural backgrounds in Seiffen, Germany (Iinuma et al. 2009); 506 ng/m 3 and 562 ng/m 3 in urban backgrounds in Ghent, Belgium (Pashynska et al. 2002;Zdráhal et al. 2002); and 772 ng/m 3 in winter in suburban sites in Elverum, Norway (Yttri et al. 2007). In Brno and Šlapanice, the average concentrations of tracers in winter in PM 1 were 273 and 646 ng/m 3 , respectively (Křůmal et al. 2015).
For PM 10 biomass burning, tracer concentrations in Krynica in 2017/2018 were 137 ng/m 3 (from 0.6 to 972 ng/ m 3 ) for LG, 13.0 ng/m 3 (from 0.8 to 99.8 ng/m 3 ) for MN and 4.7 ng/m 3 (from 0.2 to 80.9 ng/m 3 ) for GA. In the 2018/2019 season in Krynica, the tracer concentrations were higher, reaching 250 ng/m 3 (from 21.0 to 1520 ng/m 3 ), 62.1 ng/m 3 (from 7.9 to 226 ng/m 3 ) and 31.1 ng/m 3 (from 0.5 to 95.2 ng/ m 3 ) for LG, MN and GA, respectively. These results are comparable with biomass burning tracers determined in Ghent (urban), Belgium, where the concentration of LG was 477 ng/m 3 (from 121 to 1133 ng/m 3 ), that of MN was 65.9 ng/m 3 (from 17.3 to 153 ng/m 3 ) and that of GA reached 19.6 ng/m 3 (from 4.4 to 44.2 ng/m 3 ) (Zdráhal et al. 2002). In the work of Pashynska et al. (2002), the concentrations of biomass burning tracers were 420 ng/m 3 (from 96 to 1900 ng/m 3 ) for levoglucosan, 61 ng/m 3 (from 10 to 290 ng/ m 3 ) for mannosan and 25 ng/m 3 (from 4.9 to 115 ng/m 3 ) for galactosan. Higher results were observed in Porto, with a winter mean of LG equal to 774 ng/m 3 (Monteiro et al. 2018) and Elverum (suburban) winter means of 605, 167 and 4.0 ng/m 3 for LG, MN and GA, respectively (Yttri et al. 2007). Biomass consists of several main components, such as cellulose with 40-50% dry weight of wood; hemicellulose with 20-30% dry weight of wood; and lignins, combined with tannins, terpenes and other substances. The relative amount of tracers is determined by the type of biomass (softwood, hardwood, and grass) (Simoneit 2002 Table 3 shows the percentage of individual tracers in the total sum of determined compounds based on average values. Among the determined biomass burning tracers, LG is the   Cordell et al. (2016) for Leicester; GB ranged from 2.6 to 4.6, and the LG/(MN+GA) ratio ranged from 2.1 to 3.0, which is typical for softwood. For Lille, France, the LG/MN ratio varies from 2.8 to 6.7, and the LG/(MN+GA) ratio varies from 2.0 to 4.3, possibly indicating a higher hardwood contribution. However, the results of the LG/MN ratio from standard reference material on urban aerosols in Washington, USA and Prague, Czech Republic were equal to 9.4 and 4.9, respectively, suggesting that of the mixture of hardwood and softwood input into the Washington samples and Prague samples, softwood was predominant (Louchouarn et al. 2009). Caseiro and Oliveira (2012) reported the winter average LG/MN ratio in Birmingham, GB, with an urban background of 7 for fine fraction PM 2.5 and 18 for core fraction PM 2.5-10 . The ratio in Okinawa varies from 12.3 to 13.9 in winter, suggesting hardwood, softwood and hardwood mixtures or softwood and plant straw mixture burning (Zhu et al. 2015). In the 2017/2018 season in Krynica, the LG/MN ratio was higher compared to the data in the literature, which may be the result of different biomass burnings other than softwood and hardwood, such as straw or miscanthus pellets with coal. Because the atmospheric aerosol samples contain a spectrum of particulate matter, the observed biomass burning ratios must be considered carefully.
The amount of organic carbon derived from the burning of biomass can be calculated from Equation (1), which was proposed by Puxbaum et al. (2007) and Gelencsér et al. (2007), where an emission factor of 7.35 was based on the OC/LG mass emission ratio: The data are presented in Table 4.
In the winter season of 2017/2018, the OC equalled 9480 ng/m 3 , and in the season of 2018/2019, it was 8790 ng/m 3 . These results are comparable to those obtained by Zhang et al. (2010) from Guangzhou in China, where the OC concentration was 7930 ng/m 3 . In PM 1 , the OC contents in Brno and Šlapanice in the winter season of 2009 were 4.73 and 6.00 μg/m 3 , respectively, and in winter 2010, they were 9.97 and 8.74 μg/m 3 , respectively (Křůmal et al. 2015). The biomass smoke OC values calculated by Equation (1) Puxbaum et al. (2007) in winter at several sites, such as 48 ng/m 3 in Azores; 134 ng/m 3 in Puy de Dôme, France; 7739 ng/m 3 in Aveiro, Portugal; and 4800 ng/m 3 in K-Puszta, Hungary. However, the results from Krynica are comparable with those presented by Caseiro and Oliveira (2012) in Oporto in the winter season, with a roadside value of 1.5 μg/m 3 and an urban background value of 1.1 μg/m 3 . The biomass smoke OC according to Equation (1) was 10.6% of organic carbon measured in the 2017/2018 season and 20.5% of that measured in the 2018/2019 season.
The LG concentration was also used to calculate the contribution of biomass burning to OC by Equation (2), as proposed by Sang et al. (2011): The contributions of biomass smoke to OC in Krynica, according to Equation (2), in the winters of 2017/2018 and 2018/2019 were 14.4% and 28.4%, respectively. These results are compatible with the data obtained by Sang et al. (2011) from Hot Tsiu, China, with contributions in the range of 6.5 to 11%, and Zhang et al. (2008) from Beijing, with contributions ranging from 14 to 32% in PM 10 aerosols. However, the results from Krynica are lower than those reported by Caseiro et al. (2009), whereas those from Vienna range from 31.3 to 39.5%, those from Graz range from 38.4 to 58.9%, and those from Salzburg range from 34.4 to 70.2%. For Brno and Šlapanice in the winter of 2009, the relative contributions of biomass smoke to OC were 34.2 and 51.7%, respectively, and 24.1 and 20.2% in the winter of 2010, respectively (Křůmal et al. 2015).

Conclusions
The obtained results showed the following:  Author' contributions Katarzyna Janoszka performed the experiments and co-wrote the paper; Marianna Czaplicka analysed the data and cowrote the paper; Krzysztof Klejnowski collected the samples.
Funding information This research was funded by the Institute of Environmental Engineering of the Polish Academy of Sciences basic (statutory) research project no. 1a-119/2019: "Temporal and spatial variabilities in atmospheric aerosol chemical compositions as a tool for evaluating the effects of implementing air protection programmes in Poland".

Compliance with ethical standards
Conflict of interest The authors declare that they have no conflicts of interest.
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