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This study investigated atmospheric particulate matter (PM) with an aerodynamic diameter of < 2.5 µm (PM 2.5 ) observed at the Prince of Songkla University (Phuket Campus) in southern Thailand. All samples (n = 75) were collected using MiniVol™ portable air samplers from March 2017 to February 2018. Carbonaceous aerosol compositions, i.e., organic carbon (OC) and elemental carbon (EC), water-soluble ionic species (WSIS), and polycyclic aromatic hydrocarbons (PAHs) in the PM 2.5 samples were identified and quantified. We found that the average PM 2.5 concentration was 42.26 ± 13.45 µg m -3 , while the average concentrations of OC and EC were 3.05 ± 1.70 and 0.63 ± 0.58 µg m -3 , respectively. The OC/EC ratio was in the range of 2.69-16.9 (mean: 6.05 ± 2.70), and the average concentration of 10 selected ions was 6.91 ± 3.54 µg m -3 . The average concentration of SO 4 2was the highest throughout the entire study period (2.33 ± 1.73 µg m -3 ); the average contribution of SO 4 2to the major ionic components was 34%. Surprisingly, the average concentrations of NO 3and NH 4 + were relatively low. The mean ratio of [NO 3 -]/[SO 4 2-] was 0.33 ± 0.24. Strong positive correlation was found between K + and both OC and EC (r = 0.90 and r = 0.93, respectively). It is also precious to highlight that biomass burning (BB) is the major source of OC, EC and K + , which multiple studies have confirmed that the role of K + as a biomass marker. Results showed that BB episodes might play a major role in producing the observed high levels of OC. The relatively high abundance of both B[g,h,i]P and Ind suggests that motor vehicles, petroleum/oil combustion, and industrial waste burning are the primary emission sources of PAHs in the ambient air of Phuket. Interestingly, principal component analysis (PCA) indicated that vehicular exhausts are the main source of carbonaceous aerosol compositions found in the ambient air of Phuket, whereas the contributions of biomass burning, diesel emissions, sea salt aerosols and industrial emissions were also important.

Cometabolic degradation of TCE by toluene-degrading bacteria has the potential for being a cost-effective bioremediation technology. However, the application of toluene may pose environmental problems. In this study, several plant essential oils and their components were examined as alternative inducer for TCE cometabolic degradation in a toluene-degrading bacterium, Rhodococcus sp. L4. Using the initial TCE concentration of 80 microM, lemon and lemongrass oil-grown cells were capable of 20 +/- 6% and 27 +/- 8% TCE degradation, which were lower than that of toluene-grown cells (57 +/- 5%). The ability of TCE degradation increased to 36 +/- 6% when the bacterium was induced with cumin oil. The induction of TCE-degrading enzymes was suggested to be due to the presence of citral, cumin aldehyde, cumene, and limonene in these essential oils. In particular, the efficiency of cumin aldehyde and cumene as inducers for TCE cometabolic degradation was similar to toluene. TCE transformation capacities (T (c)) for these induced cells were between 9.4 and 15.1 microg of TCE mg cells(-1), which were similar to the known toluene, phenol, propane or ammonia degraders. Since these plant essential oils are abundant and considered non-toxic to humans, they may be applied to stimulate TCE degradation in the environment.