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HYDROCARBONS IN SMOKE AEROSOLS FROM CONTROLLED BURNING OF Mangifera foetida LITTER FALLSAND Panicum repens
The Malaysian Journal of Analytical Sciences, Vol 11, No 1 (2007): 29-3529
HYDROCARBONS IN SMOKE AEROSOLS FROM CONTROLLED BURNING OF Mangifera foetida LITTER FALLSAND Panicum repens
Tay Joo Hui1, Tan Hock Seng1, Norhayati Mohd Tahir*1and Mhd Radzi Abas2
1Environmental Research Group (ERG), Department of Chemical Sciences, Faculty of Science and TechnologyKolej Universiti Sains dan Teknologi Malaysia, Mengabang Telipot, 21030 Kuala Terengganu
2 Chemistry Department, University Malaya, 50603 Kuala Lumpur*Corresponding author email: hayati@kustem.edu.my
Keywords: smoke aerosols, biomass, controlled burning, hydrocarbons, polycyclic aromatic hydrocarbons.
Abstract
A study has been carried out to characterize hydrocarbons emitted from the burning of two typical garden wastes, bachang(Mangifera foetida) litter falls and grass (panicum repens). The biomass samples were burned and their respective smokeparticulate emitted was sampled using high volume sampler fitted with pre-cleaned glass fibre filters under smouldering andflaming conditions. Hydrocarbons were extracted using dichloromethane-methanol mixture as solvent and the extractsfractionated on silica-alumina column. Detection and quantification of aliphatic hydrocarbons and PAHs compounds werecarried out using GC-MS. For comparison, hydrocarbons in fresh unburnt bachang litter falls and grass were also analyzedfor aliphatic and PAHs content. Result indicated that the major components in the aliphatic fraction for all samples were nalkanecompounds which exhibited a saw-tooth pattern that is characteristic of a biogenic origin. The major components inthis aliphatic fraction for smoke particulate matters were n-alkanes in the range of C12-C36, with an odd to even carbonpredominance with CPI values ranging from 2.89-4.32 and Cmax generally at C31; total identified n-alkanes for these samplesranged from 221-939 µgg-1. On the other hand, hydrocarbons present in the fresh unburnt bachang litter falls and grassranged from C12-C36 with C27 and C33 species dominating and CPI value of 4.5 and 23.1, respectively; total identified nalkaneswere significantly higher (1530-33000 µgg-1) than those found in smoke aerosols In general, CPI > 1 indicates nalkanescontribution from epicuticular waxes thus it could be concluded that, even though the overall signature of the sourceof n-alkanes is maintained, burning seems to alter the distribution of aliphatic hydrocarbon emitted accompanied with adecrease in the CPI values and shifting in Cmax. In addition, results also indicated that burning resulted in the formation ofmany PAHs compounds in all smoke aerosols samples with total PAHs concentration ranging from 187-296 µgg-1. Freshunburnt bachang litter falls and grass on the other hand did not exhibit any PAHs compound, which clearly indicated thatPAHs were generally generated from combustion process.
Abstrak
Satu kajian telah dijalankan bagi mencirikan sebatian hidrokarbon yang dibebaskan daripada pembakaran sampel sisa lamaniaitu daun bachang (Mangifera foetida) dan rumput (Panicum repens). Sampel-sampel biojisim ini telah dibakar dalamkeadaan membara dan menyala dan zarah asap yang terhasil disampel menggunakan alat pensampelan berisipadu tinggiyang dimuat dengan penapis gentian kaca. Hidrokarbon diekstrak menggunakan campuran diklorometana-methanol (3:1)sebagai pelarut dan hasil ekstrak yang diperolehi dipisahkan dengan menggunakan turus silika-alumina. Penentuan dankuantifikasi sebatian hidrokarbon alifatik dan PAHs dijalankan dengan menggunakan GC-MS. Sebagai perbandingan,hidrokarbon daripada daun bachang dan rumput segar yang tidak dibakar juga dikaji bagi menentukan perbezaan di antaraprofil hidrokarbonnya. Keputusan menunjukkan komponen organik utama dalam pecahan alifatik untuk semua sampeladalah bersebatian n-alkana. Taburan n-alkana ini memberi bentuk gerigi yang mencirikan sumber biogenik. Komponenutama dalam pecahan alifatik adalah daripada sebatian n-alkana dalam julat of C12-C36, dengan kehadiran lebih banyakkarbon nombor ganjil berbanding karbon nombor genap. ‘Carbon preference index’ (CPI) adalah dalam julat 2.89-4.32 danCmax pada C31; jumlah n-alkana yang dikenalpasti adalah dalam julat 221-939 µgg-1. Sebaliknya, hidrokarbon alifatik yangdiperolehi daripada daun bachang dan rumput segar yang tidak dibakar adalah terdiri daripada C12-C36, dengan C27 dan C33sebagai spesis paling dominan dan nilai CPI masing-masing sebanyak 4.5 dan 23.1; jumlah n-alkana yang dikenalpastiadalah lebih tinggi (1530-33000 µgg-1) berbanding dalam zarah asap. Amnya, CPI > 1 menunjukkan sumbangan n-alkanadaripada lilin epikutikular. Kesimpulannya, walaupun keseluruhan penanda n-alkana tidak berubah, pembakaran didapatimengubah taburan hidrokarbon alifatik yang terhasil dengan penurunan nilai CPI. Keputusan juga menunjukkan pembakaranmembentuk lebih banyak sebatian PAHs dalam ketiga-tiga sampel asap dengan kepekatan dalam julat diantara 187-296 µgg-1. Daun bachang dan rumput segar yang tidak dibakar pula tidak mempunyai sebatian PAHs dan ini jelas menujukkan PAHshanya terhasil dari proses pembakaran.
Tay Joo Hui et al.: HYDROCARBONS IN SMOKE AEROSOLS FROM CONTROLLED BURNING OF30
Introduction
Biomass burning is an important primary source of soot and organic particulate matter, which influenceatmospheric chemical, optical and radiative properties through direct and indirect mechanisms [1-4]. It occurson a large scale in industrialised, developing and remote areas caused by both anthropogenic and naturalinitiation (wild fires). In Malaysia, until the year of 2000, agricultural sector had accounted for 11 percent of thegross domestic product (GDP), in which six percent of Malaysia land is under cultivation for field crops and 18percent is used for plantation agriculture [5]. The practice of burning for clearing vegetated areas and alsoagricultural wastes has significantly increased the input of organic aerosols to the atmosphere. For instance, thehaze episodes that occurred in Malaysia in September-October, 1991, August-October, 1994 and September-October, 1997 have been attributed to suspended smoke particulate matter from biomass burning in southernSumatra and Kalimantan, Indonesia. Abas et al. [6] have reported a study on atmospheric particulate duringthese haze episodes and their result indicated high concentration of levoglucosan and palmatic acid which werebiomarker compounds associated with biomass burning. In addition, Fang et al. [7] studied the solventextractableorganic compounds in the Indonesia biomass burning aerosols and the main PAHs detected wereranged from 3-6 rings with total PAHs concentration ranged from 7-46 ngm-3. These result were similar to studydone by Abas et al. [8] reported the main PAHs compound detected were 4-6 rings PAH with total PAHsconcentration of 48 ngm-3. The knowledge on the chemical composition of these aerosols is important for theunderstanding of the role of agricultural biomass waste burning emissions to the chemical processes in theatmosphere. In general, each individual plant species emits ‘chemical fingerprint’ of natural (unaltered) andthermally altered (pyrolysis) organic constituents upon burning which is source specific and unique incomposition, thus, they can be utilised as specific indicators for identifying fuel source inputs, transportmechanisms and receptor fate in samples of atmospheric fine particulate matter [2,9]. This paper presents resultof a study carried out to characterize the hydrocarbons, viz. aliphatic and polycyclic aromatic hydrocarbons(PAHs), in the aerosols emitted from the burning of two agriculture biomass waste species which was species ofgrass (Panicum repens) and litterfall of bachang tree (Mangifera foetida).
Experimental Methods
Sampling
The fresh leaves of grass were taken at a site located a few kilometers away from roadside at Kg. WakafTembusu, Gong Badak, Kuala Terengganu. This site is also located a couple of kilometers away from KUSTEMcampus. Litter falls samples of bachang tree were taken from a resident house located at Tasek Gelugor,Seberang Prai. The grass samples were separated into three portions (fresh unburnt, fresh burnt and dried burnt)while leaves samples were separated into two portions (fresh unburnt and dried burnt). The fresh unburntportion were dipped into 200 mL of dichloromethane (DCM) for 30 seconds for quantification of fresh wax;another portion was burnt fresh and the other portion was kept in an aluminium lined box and were allowed todry for a period of two weeks. The fresh and dried leaves samples were burnt completely to ember underflaming and smouldering condition. The smoke emitted during these period were collected using a high-volumeair sampler (HVS) fitted with a pre -cleaned glass fibre filter, placed approx. 1m diagonally above and to the sideof the flames in the smoke plume.
Extraction and Fractionation
Hydrocarbon compounds were extracted from the glass filter using ultrasonic agitation with DCM/Methanol(3:1 v/v) as solvent. Before extraction, two internal standards consist of n-teracosane (n-C24) for aliphaticfraction (fraction 1) and predeuterated perylene-d12 for aromatic fraction (fraction 2) were spiked into the filterpaper for recovery assessment. The extracts were concentrated to about 1 mL using rotary evaporator. Theconcentrated extracts were then fractionated into subfractions on 5% deactivated silica (230-400 mesh) and 2%deactivated alumina (70-230 mesh) columns. 20 ml of n-hexane was the used to elute the n-alkanes and PAHscompounds were eluted using a combination of 30ml of 10% DCM in hexane followed by 20ml of 50% DCM inhexane.GC/MS analysisIdentification and quantification of aliphatic hydrocarbons and the 16 priority PAHs compounds were carriedout using Shimadzu-QP2010 GC-MS. The compounds detail for aliphatic hydrocarbons were the n-alkanesranging from n-dodecane (C12) to n-hexatriacontane (C36), whilst the 16 priority PAHs compounds were asfollows: naphthalene (NAP), acenaphtylene (ACY), acenaphtene (ACE), fluorene (FLU), phenanthrene(PHEN), anthracene (ANT), fluoranthene (FTH), pyrene (PYR), benzo(a)anthracene (BaA), chrysene (CHR),benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), dibenz(a,h)anthracene (DA),The Malaysian Journal of Analytical Sciences, Vol 11, No 1 (2007): 29-3531
benzo(g,h,i)perylene (BgP) and indeno(1,2,3-cd)pyrene (IP). The sum of these 16 priority PAHs compounds isknown as total identified PAHs (TIP). The GC-MS operating conditions were as follows: fused silica column(30m x 0.32 mm i.d; 0.25 µm filmed thickness); injection temperature was set at 290? C using splitless mode.The column temperature was programmed as follow: - hold at 50? C for 1 min; 50-140 at 5? Cmin-1; 140-300? Cat 4? Cmin-1 and maintained at 300? C for 15 min. Helium was used as the carrier gas with flow rate at 2.0mLmin-1. GCMS interface was set at 300? C. Verification of peaks was carried out based on key fragment ions,retention times compared to those of external aliphatic hydrocarbons and PAHs standards, and/or mass spectra.Recovery blanksThe recovery of the multi-step procedure for the internal standard ranged from 43.6-80.4% (mean = 68.7%, stdev =14.3) for aliphatic fraction and 80.6-101% (mean = 87.4, stdev = 10.7) for aromatic fraction.
Appropriate correctionswere made to the measured concentrations.
Procedural blanks as well as solvent blanks were analysed and quantifiedto ensure that there were no significant background interferences; no PAHs and aliphatic compounds of interest weredetected in these blanks.
Results and Discussion
The major organic components identified and quantified in the aliphatic and PAH fractions are shown in Figures1 and 2.
These results are preliminary because only one burning test was conducted for each sample included inthis study. It must be conceded that distributions and abundances of the bachang litter falls and grass smokeaerosols constituents are strongly dependent on combustion conditions (e.g. smouldering versus flaming,duration) and although attempt has been made in this study to sample aerosols during both flaming andsmouldering conditions, uncertainty remains with respect to the duration of each combustion phase. Thus, thevalues reported in this study should not be used as absolute value but as a relative chemical fingerprints for eachvegetation sample.Aliphatic alkanes (n-alkanes)The distribution of individual compounds present in the aliphatic fraction of the smoke aerosols samplescollected from burning of bachang litter falls and grass are shown in Figure 1. In addition, distribution ofindividual aliphatic compounds present in fresh unburnt grass sample is also shown in Figure 1 for comparison.It can be observed that all samples exhibit the presence of straight chain n-alkanes in the range of C12-C36. Then-alkanes exhibit a strong odd-to-even carbon number predominance with the dominant n-alkanes being C29, C31and C33 [10-13]. This is also evident in our study where the n-alkanes identified ranged from C12-C36, having theodd-carbon n-alkanes exceeding their even-carbon neighbours, thus exhibiting a saw-tooth pattern which ischaracteristics of biogenic n-alkanes. Fresh unburnt bachang litter falls exhibit total n-alkanes concentration of1532 µgg-1 with Cmax at C29 whilst dry burnt bachang litter falls smoke samples exhibit total n-alkanesconcentration of 221 µgg-1; with Cmax at C27. In addition, fresh unburnt grass samples exhibit total n-alkanesconcentration of 33015 µgg-1; with Cmax at C33 whilst dry burnt grass and fresh burnt grass smoke exhibiting nalkanesconcentration of 939 µgg-1 and 708 µgg-1, respectively with both samples exhibit Cmax at C31. It appearsthat burning samples resulted in emitting of lower n-alkanes concentrations, with a slight shift in Cmax anddifferences in n-alkanes distribution. The Carbon Preference Index (CPI) calculated for carbon in the chainlength between C18-36 gave values ranging from 0.77 to 27.3 with CPI average of 7.42 and showing an odd overeven C number predominance (Table 1).
Tay Joo Hui et al.: HYDROCARBONS IN SMOKE AEROSOLS FROM CONTROLLED BURNING OF32
Figure 1: Distribution of individual aliphatic hydrocarbons in smoke and fresh unburnt samples.
Table 1: Concentration of aliphatic hydrocarbon compounds in smoke and fresh unburnt samples.
Fresh burntGrass(Panicumrepens)
smokeaDry burntGrass (Panicumrepens)
smokebDry burntBachang(Mangiferafoetida) leaves
smokeFreshunburntGrass (Panicumrepens)
Fresh unburntBachang(Mangiferafoetida)
leavesTIRAH,
µgg-1 708 939 221 33015 1532
CPI(C18-C36) 0.77 2.14 2.84 27.3 4.04
CPI(C24-C34) 3.99 2.89 4.32 23.1 4.15
Cmax C31 C31 C29 C33 C27
a with 52.9+1.23% of moisture content
b with 33.0+0.84% of moisture content
CPI (C24-C34) = 0.5[?C25 – C33 / ?C26 – C34 + ?C25 – C33 / ? C24 – C32]CPI (C18-C36) = 0.5[?C19 – C35 / ?C20 – C36 + ?C19 – C35 / ? C18 – C34]
Vascular plants synthesise epicuticular waxes containing odd C number n-alkanes usually in the C25 to C33 range
with C29 or C31 as dominant homologues, which often contribute up to 90% of all paraffins found in plant waxes
0
50
100
150
200
250
300
350
400
concentration (µgg -1 )
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
Fresh Bachang litter falls, unburnt0
2000
4000
6000
8000
10000
12000
14000
16000
concentration (µgg -1 )
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
Fresh Grass, unburnt
0
10
20
30
40
50
60
concentration (µgg -1 )
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
Dried Bachang litter falls, burnt
0
50
100
150
200
250
300
350
400
450
concentration (µgg -1 )
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
Dried Grass, burnt
0
50
100
150
200
250
300
350
400
concentration (µgg -1 )
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
Fresh Grass, burntThe Malaysian Journal of Analytical Sciences, Vol 11, No 1 (2007): 29-35
33
[11]; thus these fingerprints has been widely accepted as a signature of epicuticular wax alkanes from leaf
surfaces or sometime referred to as terrigenous plant wax source or higher plant origin [14-15]. This is evidentin n-alkanes distribution isolated from the fresh unburnt grass and bachang litter fall samples, which show acarbon distribution in the C12 to C36 range with Cmax at C33 and C29 and a CPI value of 27.3 and 4.04,respectively. Similarly, the aliphatic distributions found in the present vegetation smokes were also consistent
with earlier reports [1,2,9] and confirm an input from epicuticular wax source. It is interesting to note that,whilst retaining the characteristics of biogenic/plant waxes signature; burning of this vegetation seems to reducen-alkanes concentration emitted accompanied by a decrease in the CPI values and in the case of the fresh
samples, also resulted in a shift of Cmax. Table 1 also shows the concentration of total identified resolvedaliphatic hydrocarbons (TIRAH) for the samples. Highest concentration of TIRAH was obtained from freshunburnt grass (33015 µg/g), followed by fresh unburnt bachang litter fall (1532 µgg-1), dry burnt grass smoke(939 µgg-1), fresh burnt grass smoke (708 µgg-1) and dry burnt bachang litter fall smoke (221 µgg-1).PAHs
Figure 2 shows the distribution of individual priority PAHs present in the aromatic fraction in the smokeaerosols of samples studied. The figure reveals that all smoke samples exhibited PAH compounds. PAHcompounds are generally formed by thermal decomposition of any organic matter containing C and H atomthrough either incomplete combustion (pyrolysis) or carbonisation process. All biomass fires are pyrolysisprocesses; PAHs are formed from either the process of high temperature thermal alteration of natural productprecursors in the source organic matter or process of recombination of molecular fragment in the smoke. Resultsalso showed that phenanthrene is the most dominant component in dry burnt bachang litter fall smoke and dryburnt grass smoke, whilst benzo[g,h,i]perylene was found to be the most dominant component in fresh burntgrass smoke sample. Highest concentration of phenanthrene was found in the dry burnt bachang smoke with65.8 µgg-1 and followed by dry burnt grass smoke with 59.4 µgg-1. Fresh burnt grass smoke on the other handgave benzo[g,h,i]perylene as highest PAH component with value of 54.4 µgg-1. Another interesting featureobserved is that the low molecular weight (3-4 rings) PAH compounds (e.g. phenanthrene, fluoranthene, pyrene)are more dominant than higher molecular weight (5-6 rings) PAHs (e.g. benz[a]anthracene andbenzo[g,h,i]perylene). In addition, another interesting feature observed from the result obtained in the dry andfresh burnt grass samples where sample’s moisture content tend to reduce the PAHs content emitted in thesmoke particles.
0
10
20
30
40
50
60
70
Nap
Acy
Ace
Fle
Ph
An
Fla
Py
B[a]A
Chr
B[b]F
B[k]F
B[e]P
B[a]P
Ind
D[ah]A
B[ghi]P
Concentration, µgg-1
Dry Bachang leaves smoke Dry Grass smoke Fresh Grass smokeAbbreviations:
Nap (naphthalene), Acy (acenaphthylene), Ace (acenaphthene), Fle (fluorene),
Ph (phenanthrene), An(anthracene), Fla (fluoranthene), Py (pyrene), B[a]A (benz[a]anthracene), Chr (chrysene), B[b]F (benzo[b]fluoranthene),B[k]F (benzo[k]fluoranthene), B[a]P (benzo[a]pyrene), B[e]P (benzo[e]pyrene), Ind (indeno[1,2,3-cd]pyrene), D[ah]A(dibenz[a,h]anthracene), B[ghi]P (benzo[g,h,i]perylene).
Figure 2: Distribution of individual PAHs in smoke samples.
Tay Joo Hui et al.: HYDROCARBONS IN SMOKE AEROSOLS FROM CONTROLLED BURNING OF34
These PAHs profiles emitted from the comparison between the dry and fresh burnt grass smoke revealed thatsample’s moisture content has an influence on the PAHs content emitted in the smoke particle; the TIP emittedfrom the fresh burnt grass aerosols was significantly lower (187 µgg-1) than the dry burnt grass samples (277µgg-1) (Table 2). The amount of TIP emitted from dry burnt bachang litter fall (Table 2) was found to be similarto that of dry burnt grass sample (296 µgg-1). No PAHs was detected from the fresh unburnt grass and bachangwax which provide further evidence that PAHs are generally generated from the thermal decomposition oforganic matter.
Table 2. Concentration of the total identified PAHs (TIP) in smoke and fresh unburnt samples.
Fresh burntGrass (Panicumrepens)
smokea
Dry burntGrass (Panicumrepens)
smokeb
Dry burntBachang(Mangiferafoetida)
litterfalls smokeFreshunburntGrass (Panicumrepens)
Fresh unburntBachang(Mangiferafoetida)
litterfalls
Total PAHs(µgg-1)187 277 296 N.D. N.D.
N.D. = not detected
a.with 52.9+1.23% of moisture content
b with 33.0+0.84% of moisture content
Conclusion
Results obtained in this study showed that fresh unburnt bachang litter fall and grass samples exhibit carbondistribution in the C12 to C36 range with Cmax at C29 and C33; with CPI value of 4.15 and 27.3 respectively. nalkanedistribution from the smoke samples showed carbon distribution ranging from C12 to C36 with odd carbonpredominance and Cmax at C29 or C31 and CPI values >1 indicating that combustion process retained theepicuticular waxes and terrigenous plant input signature. It was also found that although burning of the biomasssamples retains the molecular signature of epicuticular waxes, the process seems to result in an increase of therange of aliphatic hydrocarbon emitted accompanied by a decrease in the CPI values and in the case of the freshburnt smoke samples and also resulted in a shift of Cmax. Most of the dominant PAH compounds found in thesmoke samples were of medium weight molecular compounds with lesser amount of light and higher molecularweight PAHs.
Acknowledgements
Financial supports from the Department of Chemical Sciences, KUSTEM through a grant for final year project
student (TJH) is kindly acknowledged. The use of GC-MS from INOS is also acknowledged.
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