Aliphatic and PAHs emission from open burning of selected tropical woods.

A study has been carried out to characterize hydrocarbons emitted from the burning of two wood samples that is kulim (Scorodocarpus spp.) and seraya (Shorea spp.). The woods were burned and respective smoke aerosols emitted were sampled using high volume filtration on a pre-cleaned glass fibre filters under smouldering and flaming conditions. Hydrocarbons were extracted using dichloromethane as solvent and the extracts fractionated on silica -alumina column. Detection and quantification of aliphatic hydrocarbons and PAHs compounds were carried out using GC-MS. Results indicated that the major aliphatic hydrocarbons characterized from the smoke particles were straight n-alkanes in the range of C18-C36. Both samples exhibited an odd to even carbon predominance with carbon preference index (CPI) larger than 1. In general, CPI > 1 indicates n-alkanes contribution from epicuticular waxes and thus it can be concluded that this particular signature of terrestrial plant wax is retained despite the burning process. The total identified n-alkanes for kulim wood was 734 µgg -1 with Cmax at C27 and CPI of 1.10 while seraya wood yielded 113 µgg -1 total identified n-alkanes with Cmax of C31 and CPI of 1.35. Results also indicated that burning resulted in the formation of significant amount of PAHs compounds in both the wood samples; total PAHs compounds emitted from kulim and seraya wood was 5870 µgg -1 and 5810 µgg -1 , respectively. The major PAHs compound exhibited in both wood samples were four rings PAHs (e.g. fluoranthene and pyrene) with lesser amount of two to three (e.g. acenaphthylene) and five to six rings PAHs (e.g. benzo(a)pyrene and benzo(g,h,i) perylene). In conclusion, burning of wood generated aliphatic and PAHs compounds but their distribution was influenced by the tree species. Abstrak Satu kajian telah dijalankan bagi mencirikan sebatian hidrokarbon yang dibebaskan daripada pembakaran dua sampel kayu iaitu kulim (Scorodocarpus spp.) dan seraya (Shorea spp.). Sampel-sampel kayu ini telah dibakar dan zarah asap yang terhasil disampel menggunakan alat pesampelan berisipadu tinggi yang dimuatkan dengan penapis gentian kaca. Hidrokarbon diekstrak menggunakan diklorometana sebagai pelarut dan hasil ekstrak yang diperolehi dipisahkan dengan menggunakan turus silika-alumina. Penentuan dan kuantifikasi sebatian hidrokarbon alifatik dan PAHs dijalankan dengan menggunakan GC-MS. Keputusan menunjukkan komponen organik utama yang dicirikan dari zarah asap adalah daripada sebatian alifatik rantai lurus dalam julat of C 18-C36. Kedua -dua sampel menunjukkan lebih banyak karbon bernombor ganjil berbanding karbon genap dan ‘carbon preference index’ (CPI) besar daripada 1. Amnya, CPI > 1 menunjukkan sumbangan n-alkana daripada lilin epikutikular dan boleh disimpulkan bahawa penanda khusus untuk lilin tumbuhan daratan masih kekal walaupun sampel kayu ini telah melalui proses pembakaran. Jumlah n-alkana yang dikenalpasti untuk kayu kulim adalah 734 µgg -1 dengan Cmax pada C27 dan nilai CPI adalah sebanyak 1.10, manakala kayu seraya memberi jumlah n-alkana dikenalpasti sebanyak 113 µgg -1 dengan Cmax pada C31 dan nilai CPI sebanyak 1.35. Keputusan juga menunjukkan banyak sebatian PAHs terbentuk hasil dari pembakaran kekedua sampel kayu tersebut; jumlah sebatian PAHs daripada kayu kulim dan seraya masing-masing adalah sebanyak 5870 µgg -1 dan 5810 µgg -1 . Sebatian PAHs utama yang hadir dalam kedua-dua sampel kayu adalah PAHs 4 gelang (spt. fluorantana dan pirina) diikuti dengan jumlah yang sedikit bagi dua ke tiga gelang (spt. acenaphtilina) dan lima ke enam gelang (spt. benzo(a)pirina dan benzo(g,h,i) perilina). Kesimpulannya, pembakaran kayu menghasilkan sebatian alifatik dan PAHs tetapi taburannya dipengaruhi oleh spesis pokok.