The use of polycyclic aromatic hydrocarbons molecular diagnostic ratios as a source identification tool-case study

Levoglucosan (LG) and Polycyclic Aromatic Hydrocarbons (PAHs) are organic substances emitted from variety of anthropogenic sources, mainly as a result of incomplete combustion or pyrolysis of organic material. The seasonality of PAHs emissions is a well demonstrated fact, observed in most monitoring studies, where PAHs air concentrations in winter are much higher than their respective in the summer, due to seasonally variable emission sources. Various techniques have been proposed as ideal source identification (or apportionment) tools, and much debate exists in scientific literature about the effectiveness of the proposed methodologies. The most common methodology is the use of molecular diagnostic ratios (MDRs). Based on the annual measurement campaign in rural site located on South Poland, were levoglucose and PAHs were analyzed, the MDRs were determined. The results showed that the combustion processes of solid fuels, including biomass, are mainly responsible for air quality.


Introduction
Polycyclic aromatic hydrocarbons are a large group of organic compounds which have cyclic structure and similar physicochemical properties. Although more than 100 different PAHs are known, in environmental samples 16 of them are most commonly determineddue to their toxicological properties. PAHs belong to the group of the most commonly occurring, stable organic pollutants. PAHs are emitted from natural sources, e.g.: volcanic eruptions, as well as anthropogenic sources, such as thermal transformation of solid and gaseous fuels, waste etc. [1][2][3][4]. The concentration of PAHs in the air depends on: the distance from the source of emission, the height of the emission source, meteorological conditions and the season of the year.
Various techniques have been proposed as ideal source identification (or apportionment) tools, and much debate exists in scientific literature about the effectiveness of the proposed methodologies. The most common methodology is the use of molecular diagnostic ratios (MDRs) [5,6]. The main ratios used in order to give insight about the responsible sources are given in Table 1.
The aim of the publication is to identify potential sources of PAHs emissions in rural areas, using the example of measurement campaign in health resort.

Analytical methods
Concentration of PAHs was determined by GC/MS methods. The samples were collected to the month average sample and placed in a reaction vial. Internal standard, deuterated mixture of 7 PAHs, were added. Samples were extracted in ultrasonic field with 3 portions of dichloromethane. Then, the extracts were concentrated and analyzed by using GC-2010 Shimadzu gas chromatograph (Shimadzu, USA) coupled with mass spectrometry detector equipped with a 30m, 0.25-mm i.d. HP-5MS capillary column. Calibration was performed in the range from 0.015 to 3.0 µg/mL. Precision expressed as a relative standard deviation were calculated to be from 1.3 to 12.8%.

Results
The seasonality of PAHs emissions is a well demonstrated fact, observed in most monitoring studies, where PAHs air concentrations in winter are much higher than in the summer, due to seasonally variable emission sources like space heating or cold engine start of vehicles etc. During the measurement campaign, the total PAHs concentration varied from 3.4 ng/m 3 (June 2016) to 275 ng/m 3 (January 2017). The results of the study showed a significant variation in the concentration of PAHs depending on the season. In the heating season, the total PAHs concentration was on average 100.8 ng/m 3 , while in the non-heating season only 5.9 ng/m 3 . Such a significant difference in the total PAH concentration in the air indicates a significant impact of local emission sources on air quality. Detailed profile of PAHs is presented in The obtained results indicated a much higher carcinogenic potential of dust in the heating period, compared to non-heating. The BaPE changes during the annual measurement campaign is shown in Figure 1. . It is known that the ratio ANT/(ANT+PHE) has been suggested as an indicator of petrogenic against pyrogenic sources. This ratio has been criticized in the past [5,6]. Because of the fact anthracene is more reactive than phenanthrene, and therefore their environmental fate is much different. The ratio ANT/(ANT+PHE) is therefore anticipated to change significantly from a given source. Due to the fact that the campaign was carried out in the area of the health resort, were are no large PAHs emitters in the immediate vicinity, the dependence has not been determined. The BaA/(BaA+CHR) ratio is supposedly able to discriminate between the same sources as ANT/(ANT+PHE). A value below 0.20 suggests petrogenic emissions, while a value> 0.35 cation combustion (pyrogenic emissions). During the measurement campaign, the BaA/(BaA+CHR) ratio ranged from 0.28 in August 2017 up to 0.56 in January 2018 ( Table  2). The obtained results indicate a significant impact of combustion emissions on air quality. Monthly change of BaA/(BaA+CHR) during the campaign is shown in Figure 2. FLT/(FLT+PYR) can also according to the MDRs methodology differentiate between petro-and pyrogenic sources (<0.40 and >0.40, respectively), but can also give insight on whether the pyrogenic emissions are due to fuel combustion (0.4-0.5), or due to combustion of other materials (>0.50). In the presented studies, the ratio was above 0.50 in the entire measurement campaign. The lowest value -0.51 was in October 2016, the highest -0.59 was observed in July and August 2017 ( Table 2). The value of this ratio indicates that the PAHs emission is mainly the result of biomass burning, independent of the season.