## 3 Results and Discussion  
### PM10-Bound PAH Profiles  
The results for the annual mean PM10 in this study found no statistical difference between the roadside and industrial sites. The lowest annual mean PM10 was found at the urban background site. The mean PM10 concentrations were 56.44 \(\pm\) 27.3 \(\mu\)g m\({}^{-3}\) at the roadside site, 50.69 \(\pm\) 31.1 \(\mu\)g m\({}^{-3}\) at the industrial site and 39.80 \(\pm\) 22.2 \(\mu\)g m\({}^{-3}\) at the urban background site. The total pPAHs ranged from 1.09 to 13.10 ng m\({}^{-3}\), 1.49 to 9.39 ng m\({}^{-3}\) and 0.77 to 5.20 ng m\({}^{-3}\) at the roadside, industrial and urban background sites, respectively. The annual and seasonal concentrations of individual PAHs are provided in the Supplementary Information (Table S1). Among 15 PAHs measured, PHE was the most abundant low-molecular-weight three-ring PAHs found at all sampling sites while ACE was the least abundant of all pPAHs. Concentrations of three-ring PAHs were likely to be underestimated due to their volatility and likely to partition into the gas phase. The analysis of 16 PAHs in PM10 samples in Malaysia showed that PHE and ANT were the only three-ring PAHs detected in the particulate phase [29]. PM10-bound PAHs were mostly in the range from four- to six-ring PAHs with higher molecular weights. The most abundant pPAHs were BP, IP and BbF, while BaP ranked fourth in all sampling sites (Supplementary Information). A previous study in Bangkok observed higher PAHs annual mean; however, their rankings were similar, implying that compositions of roadside PAHs have not significantly changed in the past 10 years in [30]. Annual mean concentrations of all PAHs except IP and DBA were highest at the roadside site as a result of vehicular emissions. IP and DBA mean concentrations were highest at the industrial site, indicating source-specific emissions (Figure 2). The lowest pPAH concentrations were found at the urban background site where there were no prominent sources. Traffic emissions were the main contributors of pPAHs and the mostabundant PAHs were IP, BP, BbF and BaP, which is consistent with studies previously conducted in the BMA [30; 31]. Results from previous studies have also shown high concentrations of benzo[e]pyrene and coronene at roadside sites. BP, coronene and PHE were markers for motor vehicle emissions [32]. In this study, BP and PHE concentrations were significantly higher at the roadside than other sites affirming traffic emissions. Annual mean concentrations of 15 PAHs (standard deviation) measured at the roadside, urban background and industrial sites are illustrated in Figure 2.  
Annual mean BaP concentrations at the roadside, industrial and urban background sites were 0.47\(\pm\) 0.39 ng m\({}^{-3}\), 0.35 \(\pm\) 0.27 ng m\({}^{-3}\) and 0.24 \(\pm\) 0.19 ng m\({}^{-3}\), respectively. Although PM10 concentrations found at the roadside and industrial areas were significantly higher than the WHO-recommended guideline annual mean of 20 \(\mu\)g m\({}^{-3}\), annual mean concentrations of BaP were found below the EC limit value of 1 ng m\({}^{-3}\). Daily concentrations of BaP were generally within EC and UK limits, with a few daily excursions above guideline values (Supplementary Information). PM10 and BaP concentrations measured in different cities (Supplementary Information) were compared with BaP concentrations in this study, and it was found that the results were lower than the previous study in Bangkok [20; 30] and that levels of PM10 in this study were comparable to those measured in Malaysia with slightly higher BaP concentrations in the BMA [29]. The mean concentrations of 15 pPAHs are shown in Figure 3 under different weather conditions. Most PAH concentrations at roadside and industrial sites were highest in the winter and lowest in the summer, similar to the study in Delhi [33]. PM10 concentrations were highest in the winter at all sites, suggesting higher emissions in the winter than in other seasons.