## 3 Results and Discussion  
### VOC Combustion Products of Sandalwood Incense Coils  
The main gaseous combustion by-products identified via GC/MS analysis were alkane, aromatic, chlorinated hydrocarbon compounds, and several oxygenated compounds (methanol, acetone and vinyl acetate) (Table 1). Alkane (propane and 1,3-butadiene), aromatic compounds (_i.e._, BTEXs), chloromethane, methanol and acetone are the same compounds identified by [PERSON] from burning Taiwanese incense sticks [1] and by [PERSON] _et al_. from burning incense in Thai temples [5]. Although the gaseous compounds from burning incense sticks resemble the combustion products from burning incense coils, the health hazards associated with burning incense sticks in temples do not take priority over incense coils, as people typically spend more time in the smoke from incense coils in their homes than in the smoke from sticks in temples.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Chemicals** & **Concentration (ppbv) \({}^{\text{a,b}}\)** & **Concentration (\(\text{\text{\text{\text{\text{\text{\text{\text{mg}}}}}}}}/\text{m}^{3}\)) \({}^{\text{c}}\)** \\ \hline
**Alkane Compounds** & & \\ \hline Propane & 131.84 (41.20) & 258.8 \\
1,3-Butadiene & 460.16 (57.52) & 1108.2 \\ trans-2-Butene & 42.88 (5.40) & 107.1 \\ cis-2-Butene & 40.78 (4.50) & 101.9 \\ \hline
**Aromatic Compounds** & & \\ \hline Benzene & 1.12 (0.20) & 3.9 \\ Toluene & 21.12 (2.60) & 86.6 \\ Ethylbenzene & 31.76 (3.22) & 150.1 \\ _m/p_-Xylene & 4.48 (0.41) & 21.2 \\ _o_-Xylene & 4.50 (0.20) & 21.3 \\ Styrene & 4.08 (0.51) & 18.9 \\ \hline
**Chlorinated Compounds** & & \\ \hline Chloromethane & 188.24 (23.53) & 423.2 \\ Dichloromethane & 33.12 (5.20) & 125.2 \\ \hline
**Other Oxygenated Compounds** & & \\ \hline Methanol & 54.24 (4.60) & 77.4 \\ Acetone & 76.56 (9.57) & 198.0 \\ Vinyl acetate & 28.64 (1.20) & 109.8 \\ \hline \hline \end{tabular} Notes: \({}^{\text{a}}\) The concentrations are displayed in mean values and standard deviations of triple duplicates in parenthesis; \({}^{\text{b}}\) The method detection limits for all compounds are 0.0078 ppb; \({}^{\text{c}}\) Conversed based on the mean ppb concentrations at 27 \({}^{\text{c}}\)C.  
\end{table}
Table 1: Main gaseous by-products of burning incense coil.  
Among all by-products, benzene (1.12 ppbv) is carcinogenic for leukemia; 1,3-butadiene (460.16 ppbv) and dichloromethane (33.12 ppbv) are also suspected to be carcinogens [16]. However, the 8-h TWA permissible exposure limits by the USA Occupational Safety and Health Administration (OSHA PEL) is 1 ppm for benzene, and 25 ppm for dichloromethane, which are at least 700-fold higher than the concentrations identified in this work. Notably, the 8-h TWA OSHA PEL is 1 ppm for 1,3-butadiene, relatively close to the identified concentration of 0.46 ppm. Additionally, human organs exposed to 1,3-butadiene include the eyes, respiratory system, central nervous system and reproductive system. The main effects of other alkanes and oxygenated compounds (propane, methanol and acetone) are irritation of the human respiratory tract, headache, drowsiness and dermatitis. Toluene, ethylbenzene and xylenes are minor by-products of combustion of incense coils.