## 3 Results and Discussion
### Chemical Composition
#### 3.2.3 PM\({}_{2.5}\) Associated PAHs  
Ten PAHs including fluoranthene, benzo(a)anthracene, chrysene, benzo(b,k)fluoranthene, benzo(e)pyrene, benzo(a)pyrene, perylene, indeno(1,2,3-cd)pyrene, benzo(ghi)perylene, and dibenz(ah)anthracene were quantified for all time periods. The sum of all 10 quantified PAHs is hereinafter abbreviated as PAH\({}_{\text{total}}\). Table 3 presents average PAH concentrations as well as the standard deviations, median values, and ranges for each congener associated to PM\({}_{2.5}\) samples at Graz DB. Concentrations of benzo(a)pyrene (BaP), the primary representative of PAHs and a known carcinogen (class 1 by the International Agency for Research on Cancer (IARC) [37]), ranged between 0.51 and 8.4 ng/m\({}^{3}\) (2.2 ng/m\({}^{3}\)). The highest concentrations of BaP was measured during 2 January-3 January 2017, a time period still showing influence of local activities at New Year's Eve, where PAH\({}_{\text{total}}\) concentrations reached 102 ng/m\({}^{3}\). PAH\({}_{\text{total}}\) concentrations varied from 4.6 to 56 ng/m\({}^{3}\) (17 ng/m\({}^{3}\)) over the study period and are comparable to recent results reported for other European cities [38; 39]. With proceeding time, a decreasing trend of PAH\({}_{\text{total}}\) concentrations was observed and highest concentrations could be observed for benzo(b,k)fluoranthene (B(b,k)F) followed by benzo(a)anthracene (BaA) and BaP. The toxicity of PAHs is known to differ dependent on molecular weight, and many of the heaviest PAHs are categorized by IARC as already known (class 1), probable (class 2A) or possible (group 2B) human carcinogens [37]. Therefore, we grouped the quantified PAHs in middle molecular weight PAHs (MMW, containing 4-ring congeners) and high molecular weight PAHs (HMW, containing 5- and 6-ring congeners). PAH profiles are given in Figure 8. Due to their high volatility, low molecular weight PAHs containing 2- and 3-ring congeners are not included in this work. During all time periods HMW PAHs were identified as the major components with PAH concentrations ranging from 2.9 to 42 ng/m\({}^{3}\) corresponding to 60-79% of the PAH\({}_{\text{total}}\) concentrations. The ratio of PAH\({}_{\text{total}}\) to PM\({}_{2.5}\) ranged between 0.19 and 0.88 ng/ug and the corresponding ratios of BaP/PM\({}_{2.5}\) varied between 0.02 and 0.13 ng/ug during the whole sampling period. With increasing time not only the observed PAH patterns changed, also the PAH\({}_{\text{total}}\)/PM\({}_{2.5}\) ratios decreased (Figure 8). Generally increasing temperatures result in lower PAH emissions, due to reduced residential heating activities and higher degradation of PAHs. This is already \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Abb** & **PAH** & **Mean (ng/m\({}^{3}\))** & **Standard Deviation (ng/m\({}^{3}\))** & **Median (ng/m\({}^{3}\))** & **Range (ng/m\({}^{3}\))** \\ \hline Fla & Fluoranthene & 0.56 & 0.95 & 0.38 & 0.12–2.9 \\ BaA & Benzo(a)anthracene & 2.4 & 2.9 & 1.7 & 0.45–8.4 \\ Chr & Chrysene & 2.1 & 2.2 & 1.9 & 0.57–6.7 \\ B(b,k)F & Benzo(b,k)Fluoranthene & 2.7 & 2.7 & 2.6 & 0.81–8.6 \\ BeP & Benzo(e)pyrene & 1.9 & 2.0 & 1.8 & 0.53–6.6 \\ BaP & Benzo(a)pyrene & 2.2 & 2.4 & 2.0 & 0.51–8.4 \\ Per & Perylene & 0.26 & 0.3 & 0.20 & 0.08–1.0 \\ InP & Indeno(1,2,3-cd)pyrene & 2.0 & 2.1 & 2.0 & 0.20–7.1 \\ BghiP & Benzo(ghi)perylene & 2.6 & 2.4 & 2.5 & 0.69–8.6 \\ DBA & Dibenzo(a,h)anthracene & 0.31 \({}^{*}\) & 0.6 \({}^{*}\) & 1.1 \({}^{*}\) & 0.28–2.0 \({}^{*}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: PM\({}_{2.5}\) associated polycyclic aromatic hydrocarbons (PAHs) (ng/m\({}^{3}\)) at the urban sampling station Graz DB, 2 January–31 March 2017. Overview of 14 sample pools, except for DBA\({}^{\star}\) where only 7 sample pools showed quantifiable concentrations. visible towards the end of the study period, which agrees with previously reported differences between summer and winter (38,39). A clear difference in PAHtotal/PM2.5 ratio was observed when a filter pool belonging to scenario 1 was analyzed.