Ambient organic carbon (OC) comes from the combustion of materials containing carbon, in southern Poland mainly from combustion of fossil fuels and biomass (Rogula-Kozłowska et al. 2014; Rogula-Kozłowska 2014, 2015). The amount of PM-bound OC in the air depends on these emissions and on the amounts and rate of formation of secondary organic carbon in the air (Castro et al. 1999). Ambient elemental carbon (EC) comes from incomplete combustion of materials containing carbon; in southern Poland, in spring and summer, PM-bound EC comes mainly from car exhaust emissions (Rogula-Kozłowska et al. 2014; Rogula-Kozłowska 2014, 2015). Indoor PM-bound organic and elemental carbon comes from outdoor air or indoor sources (Gupta and Bhandari 2011; Xu et al. 2015; Rogula-Kozłowska et al. 2017).
All selected beauty salons were equally affected by PM sources typical of residential areas, and Salon 1, additionally, by heavy road traffic. Salons 2 and 3 were in the same building and of the same size, they shared the hall and ventilation system, and they were two times smaller than Salons 1 and 4, which also were of the same size.
Despite similarity of the mechanisms of the inside/outside exchange of the air in Salons 1 and 4 or in Salons 2 and 3, the indoor/outdoor proportions of the PM-bound EC differed between Salons 1 and 4 and were almost the same at Salons 2 and 3; they were smallest at Salon 1 and greatest at Salon 4 (Table 1). At Salon 1, the concentrations of the road traffic emission marker, PM-bound EC (Pant and Harrison 2013; Rogula-Kozłowska 2014, 2015; Atkinson et al. 2016), both outdoors and indoors, were highest. There were no indoor PM-bound EC sources in Salon 1; its high indoor level was due to the accumulation of outdoor PM-bound EC. At Salon 4, where burning of scented candles and incense sticks (almost all the time during opening hours) was an effective indoor source of PM and PM-bound EC (Knight et al. 2001; Gupta and Bhandari 2011; Manoukian et al. 2013; Kumar et al. 2014; Zhou et al. 2015, 2016; Goel et al. 2017), the PM-bound EC originating from indoor sources prevailed over that from outdoors. This made the differences between the indoor and outdoor 8-h concentrations for both PM4-bound EC and TPM-bound EC statistically significant (Table 1). Scented candles and incense sticks were also used in Salon 3, where they were one of the causes of the correlations between the 8-h indoor concentrations of PM-bound OC and EC (Pearson correlation coefficient r ≥ 0.6); none of these four correlations occurred at any other site.
In an urban area such as Bytom, even in beauty salons where there exists an indoor PM-bound EC source, the outdoor PM-bound EC visibly contributes to the indoor one. The effect is clearer in salons where direct indoor/outdoor air exchange through the doors is possible, like at Salons 1 and 4, and especially when they are situated near an outdoor PM-bound EC source, like Salon 1.
Very high indoor PM-bound OC concentrations occurred equally in all the salons (Table 1). The vast differences between the mean indoor and outdoor concentrations of both PM4-bound OC and TPM-bound OC (Table 1) and the lacking significance of the correlation between the indoor and outdoor concentrations of OC (r < 0.6) prove strong dependency of indoor OC concentrations on indoor sources.
Biological matter or cosmetics, such as filings of nails and hard nail gels, tiny hair snippets, epidermis, would contribute to OC bound to coarse PM (i.e., particles with the aerodynamic diameter greater than 4 µm; all concentrations related to coarse PM are calculated as the difference between the respective concentrations related with TPM and PM4). For example, in Salons 1 and 4, about 40% of PM-bound OC is in coarse particles. Surprisingly, in Salon 3, which is basically a nail treatment salon, it is only 20% (Table 1). The difference may be due to the differences in the character and size between Salon 3 and Salons 1 and 4: the latter are bigger, and there are more workplaces in them, more staff and customer movement (e.g., from haircut chair to hair wash one) and more floor sweeping (because of hair cutting) that stir up and maintain the particles in the air. In small specialized salons, where there is much less of people’s movement than in bigger multi-service ones, a great part of coarse PM-bound OC stays settled and fine PM-bound OC prevails in the air.
A great part of indoor PM-bound OC in beauty salons comes from using of a variety of cosmetics; they contain hydrocarbons, alcohols, esters, phenols, acids, etc. (Cosmetic Ingredient Review 2008; Nohynek et al. 2010; Rothe et al. 2011; Williams et al. 2016). Most of them are applied as aerosols directly from spray cans and bottles or atomizers. Some (hybrid) nail polishes, acrylics, and gels require UV hardening; hair dyes and brighteners, various hair masks and conditioners are applied hot. Besides organic compounds, all used cosmetics and detergents contain also other substances, e.g., ammonia, which can react with indoor ambient organics (Cosmetic Ingredient Review 2008; Tsigonia et al. 2010; Pak et al. 2013; Madnani and Khan 2013; Arezes et al. 2014; de Gennaro et al. 2014; Aparecida da França et al. 2015; Mancini et al. 2017). Therefore, it is not surprising that PM4-bound OC made 60–80% of TPM-bound OC in average. Moreover, being inside, both coarse and fine PM particles, no matter if they come from outdoor or indoor sources, can be enriched in volatile or semi-volatile organic compounds, as it was already observed for polycyclic aromatic hydrocarbons and mercury in university teaching rooms (Majewski et al. 2016; Rogula-Kozłowska et al. 2017).
The differences between the indoor and outdoor behaviors of PM-bound carbon at the beauty salons can be clearly seen in the shares of EC and OC in total carbon TC (TC = EC + OC). The average shares of PM-bound OC in PM-bound TC were generally higher indoors than outdoors at each beauty salon (Fig. 1). The greatest differences occurred at Salons 2 and 3, the two salons smaller in size and with smaller crew than multi-service Salons 1 BS4. The less turbulent air together with significant gaseous chemical emissions from applied cosmetics (volatile organic compounds (VOC), ammonia, formaldehyde, ozone, etc.) in Salons 2 and 3 was favorable for the formation of secondary carbonaceous matter that bound later to fine PM (Ali et al. 2017). Through the Salons 2 and 3 common hall, the gaseous chemicals could easily migrate from one to another (e.g., ozone from ozone hair treatment in Salon 2 to Salon 3). The smallest differences between the indoor and outdoor means for PM4-bound OC and EC contents of TC, and the higher indoor than outdoor mean TPM-bound EC content of TC, occurred at Salon 1 (Fig. 1). This might have been the effect of rising the indoor EC to the level higher than in other salons by direct emissions of EC from the big road (Table 1), what, in turn, might have intensified the inhibition of the transformations of gaseous precursors of OC by absorbing sunlight or adsorbing volatile compounds. The indoor transformations of gaseous OC precursors seem to be more intense in the salons similar to Salons 2 and 3 than in salons such as Salons 1 and 4. The presence of a strong PM-bound carbon source near a salon (like the big road at Salon 1) is also important to indoor and outdoor secondary OC formation. The explanation of such a distribution of the PM-bound TC mass between OC and EC at the sampling sites is rather hard because, among other things, it should involve the evaluation of the amounts of secondary organic matter in the indoor air of the salons. However, the transformations of indoor VOCs can probably be one of the main factors of the formation of indoor PM-bound OC in the salons, just as it is in the atmosphere.
The two general patterns of distribution of TPM- and PM4-bound OC among the thermal fractions (arising during the PM thermal analysis) at the sites are presented in Fig. 2.
Their similarity to each other is probably due to the high mass contributions of PM4 and PM4-bound OC to TPM and TPM-bound OC, respectively (Table 1). Again, the differences between Salons 2 and 3 are very small for both TPM and PM4. Instead, at each site, the distributions of indoor and outdoor PM-bound OC are entirely different for both TPM and PM4.
The ambient secondary compounds arising from VOCs in photochemical reactions or from organic vapor condensation have relatively low molecular weights and boiling temperatures (Froines and Garabrant 1986; Cosmetic Ingredient Review 2008; Xu et al. 2015; Lachenmeier et al. 2017). During the analysis of PM for OC, they are released as OC1 at the temperature not exceeding 200 °C (Cavalli et al. 2010). Mean (in the measuring period) OC1 mass contribution to PM-bound OC was greater outdoors than indoors at all the sampling sites (Fig. 2). It does not mean that the penetration of secondary organic matter (quite adequately represented by OC1 outdoors) from the outside to the inside was not so efficient as that of primary matter—this only means that the remaining OC components were of greater importance indoors than outdoors at all sites. Inside the salons, besides secondary compounds, OC1 comprised also primary organic compounds, such as low boiling point alcohols (ethanol, lauryl alcohol), acids (salicylic), solvents (camphor), thickeners (bee wax) (Cosmetic Ingredient Review 2008; Williams et al. 2016; Lachenmeier et al. 2017). The thermal fractions OC2 and OC3 are dominant indoors at all the sites, and their contributions to OC outdoors are also significant. They contain quite complex organic compounds, and their boiling temperatures are between 300 and 650 °C. Probably, they are the basic components of the cosmetics and chemicals used in the salons, such as glycerin, paraffin oil, vaseline, various polymers and copolymers (chitosan, collagen), salts (sodium laureth sulfate), acids (pantothenic and stearic) esters and diols (cetyl palmitate), proteins (keratin) (Cosmetic Ingredient Review 2008; Nohynek et al. 2010; Rothe et al. 2011; Williams et al. 2016; Lachenmeier et al. 2017). Although OC4 contents in PM-bound OC indoors and outdoors do not differ much at any site, it is rather clear that the OC4 composition indoors depends on the salon profile. Most probably, organic matter decomposed at 650 °C consists of cellulose and its derivatives coming from cosmetic fillers and thickeners and from biological matter (fragments of skin, nails, hair).