- Email: [email protected]
Characterization of polar organics in airborne particulate matter
CHARA~ERIZATION OF POLAR ORCANICS IN AIRBORNE PAR~C~ATE BARER Y. YOKCVVCHI and Y. AMBE The Division of Cbemistry and physics, National Institute for Enviro~eutal Japan
Studies, Yatabe, Ibaraki 305,
(First receive& 18 Qcmber 1985 and infinui&rm 24 Februury 1986)
Abstmet-The metbanal-extractable bighiy polar organics in atmospbcric aerosol were characterized using GC-MS. Dicarboxylic acids having 2-16 carbon numbers were detected with a total concentration of 172 ng m-‘. Azelaicacid (C,) was the most abundantd&id and it possibly originated from the ozonolysis of unsaturated carboxylic acids such as oleic acid and linoleic acid, which mainly originate from terrestrial plants. A compound, wbicb was tentatively idtntified as tctrabydrofuroic acid, contributed to about loo/, of the highly polar organics. Other ~l~un~io~~ compounds found in the samples included some ketocarboxylic acids and aromatic acids such as pbtbalic acids, anisic acid and vanillic acid. Key word index: Dicarboxylic acids, polar organics, aerosols, axelaic acid.
Many anthropogenic gaseous organic pohutants are transformed in the atmosphere by photochemical reactions, Some of these reaction products result in the formation of particles (Finlaysoo and Pit&, Jr., 1976), ahhough many of the transfo~ation m~hanisms have not been fully understood. Po~yfunction~ reaction products such as dicarboxylic acids (Schuetzle ef al., 1975) are highty polar and are very effective in the production of lint-uttering aerosols, because of their extremely reduced vapor pressure (O’Brien er al., 1975). On the other hand, gaseous and particulate organics from natural sources such as plants and soil are also introduced into the atmosphere. They also oxidize in the atmosphere and are changed to different compounds with higher polarity. A comprehensive understanding of these secondary aerosols in the atmosphere might ahow us to ascertain the photochemical reaction products in the atmosphere and to understand the mechanisms of the atmospheric reactions of primary emitted substances. Although there are a considerable number of studies on monocarboxylic acids in the atmosphere (Kawamura er at., 1985; Gagosian et nl., 1982; Simoneit and Maxurck, t982), few studies have been undertaken for dete~inin~ the chemical composition of the more polar fractions in atmospheric aerosols, except for the identification of some aliphatic dicarboxylic acids by Grosjean et al. (1978) and the detection of polyols by Wauters et ai, (1979). In this paper, we report a c~~ctcr~tion of highly polar organics of the airborne particles sampled in a suburban area in Japan, including quantification of dicarboxylic acids and detection of unknown compounds in the en~ronment using gas chromatograph-mass spectrometry.
Sample collection
Aerosol samples were collected in the Tsukuba area, 60 km NE of Tokyo, which is a suburban arCa surrounded by agricultural fields and forests, and subjected to occasional motor vehicle traffic. Sampling was made on 28 and 29 April 1985, in fine weather. Aerosof was sampled by filtering air through a Pallflex 8” x 10” quartz fiber filter using a Kimoto Model 12OA high-volume air sampler with a capacity of 1 m3 mitt-‘.Tbe filters were heated at 250°C in vacuoprior to sampling. For a reference, surface soil was sampled in this area and the analytical procedures on the aerosol were also applied to the soil samples. SmnpIe extraction Soxhlet extraction of the filters was undertaken in an allglass apparatus with 100 ml of high purity methylene chloride for 4 hand subsequently with 100 ml of high purity methanol for 4 h. After filtration, the extracts were evaporated to dryness by means of a rotary evaporater in a water bath maintained below 40°C. As metbanol might also extract some inorganic substances, the residue of the methanol extract was redissolved with dicbloromethane followed by filtration and drying. The residues were weighed and stored in the dark at 4°C until analysis. The acid faction of the dichloromethan~ extract was isolated from the other fractions by thin layer chromatography. The acid fraction of the dichloromethane extract and the methanol extract which was considered IO contain highly polar organics were treated with a freshly prepared ether solution ofdi~omethane to esterify free acids. GC and W-MS
procedures
Analytical gas chromatography was performed on a Wtwlttt-Packard WOA gas chromatograph equipped with a tIame ionization dttector and fitted with a grass capillary column (0.2 mm ID x 25 m) coated with methyl silicone (like Gv-1). The temperature was programmed from 30°C to 300°C at 8°C min- ’ (Mmin) followed by 4°C min- ” and then remained isothermal. The extracts were injected into the GC in splitless mode. Computt~~ GC-MS analyses were carried out on JMS DX-300 with a Hewlett-Packard 5710A
1727
Y. Yo~ouctttand Y. AWE
1728
the other diacids were quantified assuming that they have the same ~nsitivity to the FII3 as that of CiO runs. Cyclic scans of the mass spectrometer from mass 35 up diacid. The total concentration of al1the dicarboxylic to mass 600 were repeated every 2 s. The mass spectral data acids was 172 ng m-O, which corresponded to 11% of were processed using a JMS_3W/3saO MS Data Analysis the methanol extract. The distribution (concentration system. vs carbon number) of dicarboxylic acids is shown in Recouery Fig. 2, together with that ofmonocarboxylicacids. The Recoveryof diirboxyhc acids (sue&tic acid, ghttaric acid distribution of dicarboxylic acids exhibited no carbon and aaebtic acid) from quartz fiber filters were investigated. number predominance (even to odd), while monocarTen micrograms of eaeh standard diaeid was added onto a blank filter, and the entire analytical process was conducted boxylic acids had a saw-teeth distribution (even > odd), suggesting their terrestrial plant origin on this filter. Recovery efhciency of diacids from the filter ranged from 76 to 86 ye, although their extraction efficiency (Simoneit and Mazurek, 1982;Gagosian et al., 1982). from the sampled filters would be lesser because of their Axelaicacid (C,) was the most abundant dicarboxylic adsorption to other substances collected on the filters. acid, and Cta-C,s di~r~xylic acids were present at Therefore, tbe q~nti~tive values of dicarboxylii acids the lowest concentration level. The predominance of reported in this study, where their recovery was supposed to azelaic acid to other diacids has also been observed by be 80%. should be considered to be lower fiits. other researchers in the analyses of precipitation. Lunde et al. (1977)analyzed 22 samples of snow and RESULTSAND DKCUSSION rain in Norway and detected dicarboxylic acids having C,-C, I, of which only C, and Cg acids were present in The total aerosol concentration was 61 pg m-s, of which 9.9 >; was extracted with CHsCl, and 2.5% was all the samples, suggesting that Cs and C, diacids are extracted with the following extraction with MeOH. present commonly in the atmosphere. However, Grosjean et al. (1978) reported that succinic acid (C,) The analytical results for the methanol extract, which was considered to contain highly polar organics of and glutaric acid (C,) were relatively important in the interest, were carefully examined. Figure 1 shows the aerosol during a smog episode in the Los Angelesarea, gas chromato~~ of the methyl ester&d sample of and azelaic acid was a minor ~mponent of their the methanol extracts of the aerosol. The ~m~unds sample. They suggested that cyclic olefin may be an identified using GC-MS are listed in Table 1,together important class of hydrocarbon precursor leading to with their structure. the formation of dicarboxylic acids. However, it seems impossiblethat azelaic acid and higher diacids found in Aliphatic dicarboxylic acids this study are formed from cydic olefins, because their In addition to C,-C,o dicarboxylic acids prereporprecursor, large cyclic olefins having more than nine ted by Grosjean et al. (1978), oxalic acid (C,) and carbons, have not been found in the atmosphere. dicarboxylie acids having 11-16 carbons were for the Diolefins and unsaturated monocarboxylic acids may first time found as constituents of atmospheric aerosol. also be precursors of dicarboxylic acids. Although None of these dicarboxylic acids were found in the acid higher diolefins having five or more carbons have not fraction of the dichloromethane extract, while most been detected in the atmosphere, unsaturated monomonocarboxylic acids were present in the acid fraction carboxylic acids produced abundantly by plants are of the dichloromethane extract. Quantitative determi- known to be introduced into the atmosphere. Oleic nation of the dicarboxylic acids was performed using acid and linoleic acid are very ubiquitous olefinic acids GC. Diacids in the C2-Cto range were determined and both of them have a double bond at the ninth using calibration curves of authentic standards, and carbon from their carboxyl group. Therefore, the
gas c~ro~sog~ph. The GC conditions in the GC-MS analyses were identical to those in the above GC analytical
ii
20
30 -
40
50
Tirse(min)
Fig. 1. Gas chromatogramof the methylstedmethanolextractof the aerosolssampledat Tsukubadistrictsin Japan
C~~ctcr~tion Table I. Compounds
found in the highly polar fraction (methanol-extractable) atmospheric aerosols
of the
No.* 4
Formula
Compound
1729
of polat organics in airborne particul3te matter
VOOH
Oxalic acidt
I
COOH 3-Hydroxy
2
YOOH
isovaieric acidt
CHI CH+-OH CHJ 3
COOH
Maloic acids
dH1 dOOH 2-Furoic acidt
~Oxo-~ntanoic
\O/ c)r acid? CH
Tetrahydro
Succinic
4
COOH
2-furoic acid*
acid$
52
,
,-C-(CH ),COOH 0
t‘r
COOH
yoox f?-h COOH
Methyl succinic acid$
700” CH,TH FH2 COOH
Benzoic acidf
COON
Clutaric acid$
CyOO”
IO
m-f,),
doow
t-Methyl
~lut~ri~ acid?
FOOH
II
CH,_CH (CH,), Salicylic acidi
cioow COOH
12
Adipic acid$
yo0l-l
13
(YHA COOH 3-Methyl adipic acids
COOH &H, CH,-LH &HZ), 6OOH
14
Y. YOKOUCHIand Y. AMBE
1730 Table 1. (Confd.)
Compound
No.* 8
Formula
Pimelic acid*
Anisic acid+//
Wydroxy
benzoic acidt
17
YOOH
0 0
Phlhalic acidt,:
a 0
OH COON
18
COON
Phthalic anhydridet.5
18
Suberic acid*
COOH
19
4+Oxo-pimelic acidt
COOH
20
h-M*
dOOH
p-Hydroxy benzoic acidt
COOH
21
Te~~phfhalic acidt
YOOH
22
COOH
Characterization of polar organic3 in airborne particulate matter
1731
Table 1. (Contd.) Compound Isophthalic acidt
COOH
b
Vanillic acidt ,)I
No: 4
Formula
0
23
COOH
FOOH
24
OCH,
Azelaic acid$
3P-Dimethoxy benzoic acidt.11
Sebacic acidt
COOH (CHz), COOH COOH I
25
FOOH
21
26
(FH,), COOH Myristic acidt Undecanedioic acid*
C,,H,,COOH FOOH
28 29
(fH& COOH Pentadecanoic acidt Dodecanedioic acid*
C,,H,,COOH FOOH
30 31
(FH& COOH
Biphenyl dicarboxylic acid* HOOC @@CoDH
32
Fkrnitic acidt
C,,H,,COOH
33
Tridecanedioic acid l
YOOH
34
(FH,), , COOH Heptadecanoic acidt
C,,Cs,COOH
35
Tetradacanedioic acid l
$OOH
36
(YH,),, COOH
Y.
1732
Yo~oucmand Y. AMBE
Table 1. (Contd.) Compound
Formula
No: 8 37
Linoleic acidt
C1,H,,COOH
Oltic acid?
C,7H&XOH
38
Stearic acidt
C, ,H,,COOH
39
Pentadecanedioic acid*
YOOH
40
(FH2f13
COOH Nonadecanoic acid? Hexadecanedioic acid*
C,sH,,COOH
41
YOOH
42
(CH2h4
COOH Dehydroabje~ic acidt
Eicosanoic acidt
C,gH,,COOH
44
Heneicosanoic acid+
C20H,,COOH
45
Docosanoic acidt
C,,H,3COOH
46
Tricosanoic acid?
C2,H,,COOH
47
Tetracosanoic acidt
C&,,COOH
48
* Identification was only based on the rationalization of mass spectra. t The mass spectra corresponded fully with published reference spectra. ~~denti~~tions were performed using authentic standards. $Numbers show GC peaks of the methyl esterified compounds in Fig+ 1. 11.5See text.
attack of 0s on these olefinic acids would cause Criegce split at the ninth carbon and could produce azelaicacids by the reaction outlined in Fig. 3.This was supported by the data on mon~~xylic acids in the aerosol and soil. In spite of the similar distributions of aliphatic carboxylic acids in the aerosol and soil, oleic acid and linoleic acid were much reduced in the aerosol sample. This fact implied that these olcfinic acids had been changed or removed in the atmosphere. It is unknown whether these olefinic acids undergo ozonolysis in the gas phase or on particulates. In suburban areas, higher diacids, which are not considered to be produced pbotochemicaIIy from known pollutant gases,might be produced from the reaction of olefinic acids originated from terrestrial plants.
The presence of both phthalic acid and phthalic anhydride was determined from the W-MS analysis of the methanol extract sample prior to ~teri~~tion. Terephthalicacid and isophthalicacid were also found in the aerosol. Anisicacid identified in this study might be originally p-hydroxy benzoic acid, as hydroxy groups might also be methylated by the treatment of the sample with diazomethane. For the same reason, vanillic acid and 3,4-dimethoxy benzoic acid might result from 3.4~ihydroxy benzoic acid. Hefermyctic carboxylic acids
An unknown compound, which corresponds to the peak number 6 in Fig. 1,and amounts to iO.?/,of all the
1733
Characterization of polar organics in airborne particulate matter
.3
Hrosols
hl~rboxylic
acids
1000
800
0
Dicarboxylic acidr
0
2
4
8
8
10
12
14
Carbon
18
18
20
22
24
28
28
30
‘0
number
Fig. 2. Distributions of dicarboxylic acids and monocarboxylic acids of the aerosols. T23 : linear and aliphatic acids, = : branched-chain dicarboxylic acids, biT1: olcic acid, m: linoleic acid.
Ii 0,‘~0”
_
H-$-R H-C-@H$?COoH
+
03
-
‘o+-tc~cocm H
9 RCH
1
9
1 (oleic
acid
9 ~C-(C~~.COOH
R- =++&cw3 linoleic
acid
-
&CH-
t
v *OtZQR 4 HOOGR
R - Ct+@i * CH(CH&-C% i
+ *OO~HfCHr),COOH
1 IiOOC-fCH&COOH azelaic acid
/ Fig. 3. Formation of azelaic acid
from the ozonolysis of oleic acid and linoleic acid.
peak area in the chromatogram, was tentatively identified to be tetrahydro 2-furoic acid from the interpretation of its mass fragmentation pattern (Fig. 4). The mechanism of formation and the precursor of tetrahydro 2-furoic acid is of great interest, since it was the most abundant substance in the methanol extract of the aerosol. The presence of tetrahydrofuroic acid has not been reported before this study. One possible reason for this is that the technique of esterification, usually utilized for GC analyses of acidic compounds, might enhance evaporation of small molecules like tetrahydrofuroic acid. Mechanisms of producing tet~hydrofuroic acid are unknown, and a natural-origin compound might be a source of this acid iike azelaic acids.
Furoic acid was also found in the aerosol for the first time. One of the precursors of this acid might be furfural which is a component of diesel emission and plant vapor (Graedei, 1978). These furan-type compounds may also originate from the oxidation of isoprene (Gu et af., 1985). Keto-carboxylic acids 4-Oxo-pentanoic acid and Coxo-pimelic acid were detected in the aerosol sample. These keto-carboxyiic acids might also be produced photochemically from hydrocarbon precursors. Several other compounds were also identified to be keto-carboxylic acids from their mass spectra, although the substituted site of the carbonyl group was not specified.
1734
50
100
150
Fig. 4. Mass spectrum of the methyl ester of the most predominant acid in the highly polar fraction of the aerosols, corresponding to peak No. 6 in Fig. 1. In this study, major components of the highly polar organ& in the atmospheric aerosols were identified. They were dicarboxylic acids (C1-C16), heterocyclic acids, keto-carhoxylic acids and multifunctional aromatic acids, which were considered to he atmospheric reaction products of precursors. ft was noteworthy that olefinic atrboxytic acids, oleic acid and linole& acid may result in the formation of ditzuhoxylic acid (azclaic acid, C,) in the atmosphere. There still remain many other polar compounds which were not identi-
Gagosian R. B., Zafiriou 0. C., Peltzer E. T. and Alford J. B. (1982)Lipids in aerosols from the tropical north Pacific temporalvariability.J. geopfiys.Res. 87, 11,133-l 1,144. Graedcl T. E. (1978)C/ten&l Compoundsin the Atmosphere, p. 175.Academic press,New York. GrosjeanD, vanCauwenbcrghc IL, S&mid3.P., Kclley P. E. and Pitts, Jr. J. N. (!978) Identification of C,-C,, aliphatic dicarboxylicacids in airborne particulate m&r. &tvir. Sci.
fid
Kawamura K., Ng L-L and Kaplan I. R. (1985) Determination of organic acids (C,-C,e) in the atmosphere, motor exhausts and engine oils. Envir. Sci. Techno!. 19, 1082-1086. Lunde G., Getbcr J., Gjos N. and Lande M.-B. S. (1977) Organic micropollutants in precipitation in Norway. Atmospheric Enuiroamenr 11, 1007-1014. O’Brien R. J., Holmes J. R. and Bockian A. H. (1975) Formation of photochemical aerosol from hydrocarbons. En&r. Sci. Technot.9, 568-576. Schuetxle D., Cronn D. and Crittenden A. L. (1975) Molecular composition of secondary aerosol and its possible origin. Enutr. Sci. Technol. 9, 838-845. Simoneit 8. R. T. and Maxurck hi. A. (1982)Organic matter of the troposphere-II. Natural background of biogcnic lipid matter in aerosols over the rural western United States. Armspheric Environment 16, 2139-2159. Wauters E., Vatqaever F. Sandra P. and Verxelc M. (1979) Polar organic fraction of air particulate matter. J. CkromntogT.170, 133-l 38.
in this study. The identification
of these com-
pounds and their*precursorscould yield some important information about the environmental fate of manmade and natural-origin compounds in the atmosphere.
Ackrtowledgements-We
wish to thank Dr H. Shiraishi and Mr H. Mukai for their useful discussions. We also thank Mr H. Ito for his help in GC-MS analyses.
REFERENCES
Finlayson B. J. and Pitts, Jr. J. N. (1976)Photochemistry of the polluted troposphere. Science 192, 11l-l 19.
Technol. 12,313-317.
Gu C-f, Rynard C. M., Hendry D. G. and Mill T. (1985) Hydroxyl radical oxidation of isoprene. Enuir. Sci. Techno/. 19, 151-155.
Studies, Yatabe, Ibaraki 305,
(First receive& 18 Qcmber 1985 and infinui&rm 24 Februury 1986)
Abstmet-The metbanal-extractable bighiy polar organics in atmospbcric aerosol were characterized using GC-MS. Dicarboxylic acids having 2-16 carbon numbers were detected with a total concentration of 172 ng m-‘. Azelaicacid (C,) was the most abundantd&id and it possibly originated from the ozonolysis of unsaturated carboxylic acids such as oleic acid and linoleic acid, which mainly originate from terrestrial plants. A compound, wbicb was tentatively idtntified as tctrabydrofuroic acid, contributed to about loo/, of the highly polar organics. Other ~l~un~io~~ compounds found in the samples included some ketocarboxylic acids and aromatic acids such as pbtbalic acids, anisic acid and vanillic acid. Key word index: Dicarboxylic acids, polar organics, aerosols, axelaic acid.
Many anthropogenic gaseous organic pohutants are transformed in the atmosphere by photochemical reactions, Some of these reaction products result in the formation of particles (Finlaysoo and Pit&, Jr., 1976), ahhough many of the transfo~ation m~hanisms have not been fully understood. Po~yfunction~ reaction products such as dicarboxylic acids (Schuetzle ef al., 1975) are highty polar and are very effective in the production of lint-uttering aerosols, because of their extremely reduced vapor pressure (O’Brien er al., 1975). On the other hand, gaseous and particulate organics from natural sources such as plants and soil are also introduced into the atmosphere. They also oxidize in the atmosphere and are changed to different compounds with higher polarity. A comprehensive understanding of these secondary aerosols in the atmosphere might ahow us to ascertain the photochemical reaction products in the atmosphere and to understand the mechanisms of the atmospheric reactions of primary emitted substances. Although there are a considerable number of studies on monocarboxylic acids in the atmosphere (Kawamura er at., 1985; Gagosian et nl., 1982; Simoneit and Maxurck, t982), few studies have been undertaken for dete~inin~ the chemical composition of the more polar fractions in atmospheric aerosols, except for the identification of some aliphatic dicarboxylic acids by Grosjean et al. (1978) and the detection of polyols by Wauters et ai, (1979). In this paper, we report a c~~ctcr~tion of highly polar organics of the airborne particles sampled in a suburban area in Japan, including quantification of dicarboxylic acids and detection of unknown compounds in the en~ronment using gas chromatograph-mass spectrometry.
Sample collection
Aerosol samples were collected in the Tsukuba area, 60 km NE of Tokyo, which is a suburban arCa surrounded by agricultural fields and forests, and subjected to occasional motor vehicle traffic. Sampling was made on 28 and 29 April 1985, in fine weather. Aerosof was sampled by filtering air through a Pallflex 8” x 10” quartz fiber filter using a Kimoto Model 12OA high-volume air sampler with a capacity of 1 m3 mitt-‘.Tbe filters were heated at 250°C in vacuoprior to sampling. For a reference, surface soil was sampled in this area and the analytical procedures on the aerosol were also applied to the soil samples. SmnpIe extraction Soxhlet extraction of the filters was undertaken in an allglass apparatus with 100 ml of high purity methylene chloride for 4 hand subsequently with 100 ml of high purity methanol for 4 h. After filtration, the extracts were evaporated to dryness by means of a rotary evaporater in a water bath maintained below 40°C. As metbanol might also extract some inorganic substances, the residue of the methanol extract was redissolved with dicbloromethane followed by filtration and drying. The residues were weighed and stored in the dark at 4°C until analysis. The acid faction of the dichloromethan~ extract was isolated from the other fractions by thin layer chromatography. The acid fraction of the dichloromethane extract and the methanol extract which was considered IO contain highly polar organics were treated with a freshly prepared ether solution ofdi~omethane to esterify free acids. GC and W-MS
procedures
Analytical gas chromatography was performed on a Wtwlttt-Packard WOA gas chromatograph equipped with a tIame ionization dttector and fitted with a grass capillary column (0.2 mm ID x 25 m) coated with methyl silicone (like Gv-1). The temperature was programmed from 30°C to 300°C at 8°C min- ’ (Mmin) followed by 4°C min- ” and then remained isothermal. The extracts were injected into the GC in splitless mode. Computt~~ GC-MS analyses were carried out on JMS DX-300 with a Hewlett-Packard 5710A
1727
Y. Yo~ouctttand Y. AWE
1728
the other diacids were quantified assuming that they have the same ~nsitivity to the FII3 as that of CiO runs. Cyclic scans of the mass spectrometer from mass 35 up diacid. The total concentration of al1the dicarboxylic to mass 600 were repeated every 2 s. The mass spectral data acids was 172 ng m-O, which corresponded to 11% of were processed using a JMS_3W/3saO MS Data Analysis the methanol extract. The distribution (concentration system. vs carbon number) of dicarboxylic acids is shown in Recouery Fig. 2, together with that ofmonocarboxylicacids. The Recoveryof diirboxyhc acids (sue&tic acid, ghttaric acid distribution of dicarboxylic acids exhibited no carbon and aaebtic acid) from quartz fiber filters were investigated. number predominance (even to odd), while monocarTen micrograms of eaeh standard diaeid was added onto a blank filter, and the entire analytical process was conducted boxylic acids had a saw-teeth distribution (even > odd), suggesting their terrestrial plant origin on this filter. Recovery efhciency of diacids from the filter ranged from 76 to 86 ye, although their extraction efficiency (Simoneit and Mazurek, 1982;Gagosian et al., 1982). from the sampled filters would be lesser because of their Axelaicacid (C,) was the most abundant dicarboxylic adsorption to other substances collected on the filters. acid, and Cta-C,s di~r~xylic acids were present at Therefore, tbe q~nti~tive values of dicarboxylii acids the lowest concentration level. The predominance of reported in this study, where their recovery was supposed to azelaic acid to other diacids has also been observed by be 80%. should be considered to be lower fiits. other researchers in the analyses of precipitation. Lunde et al. (1977)analyzed 22 samples of snow and RESULTSAND DKCUSSION rain in Norway and detected dicarboxylic acids having C,-C, I, of which only C, and Cg acids were present in The total aerosol concentration was 61 pg m-s, of which 9.9 >; was extracted with CHsCl, and 2.5% was all the samples, suggesting that Cs and C, diacids are extracted with the following extraction with MeOH. present commonly in the atmosphere. However, Grosjean et al. (1978) reported that succinic acid (C,) The analytical results for the methanol extract, which was considered to contain highly polar organics of and glutaric acid (C,) were relatively important in the interest, were carefully examined. Figure 1 shows the aerosol during a smog episode in the Los Angelesarea, gas chromato~~ of the methyl ester&d sample of and azelaic acid was a minor ~mponent of their the methanol extracts of the aerosol. The ~m~unds sample. They suggested that cyclic olefin may be an identified using GC-MS are listed in Table 1,together important class of hydrocarbon precursor leading to with their structure. the formation of dicarboxylic acids. However, it seems impossiblethat azelaic acid and higher diacids found in Aliphatic dicarboxylic acids this study are formed from cydic olefins, because their In addition to C,-C,o dicarboxylic acids prereporprecursor, large cyclic olefins having more than nine ted by Grosjean et al. (1978), oxalic acid (C,) and carbons, have not been found in the atmosphere. dicarboxylie acids having 11-16 carbons were for the Diolefins and unsaturated monocarboxylic acids may first time found as constituents of atmospheric aerosol. also be precursors of dicarboxylic acids. Although None of these dicarboxylic acids were found in the acid higher diolefins having five or more carbons have not fraction of the dichloromethane extract, while most been detected in the atmosphere, unsaturated monomonocarboxylic acids were present in the acid fraction carboxylic acids produced abundantly by plants are of the dichloromethane extract. Quantitative determi- known to be introduced into the atmosphere. Oleic nation of the dicarboxylic acids was performed using acid and linoleic acid are very ubiquitous olefinic acids GC. Diacids in the C2-Cto range were determined and both of them have a double bond at the ninth using calibration curves of authentic standards, and carbon from their carboxyl group. Therefore, the
gas c~ro~sog~ph. The GC conditions in the GC-MS analyses were identical to those in the above GC analytical
ii
20
30 -
40
50
Tirse(min)
Fig. 1. Gas chromatogramof the methylstedmethanolextractof the aerosolssampledat Tsukubadistrictsin Japan
C~~ctcr~tion Table I. Compounds
found in the highly polar fraction (methanol-extractable) atmospheric aerosols
of the
No.* 4
Formula
Compound
1729
of polat organics in airborne particul3te matter
VOOH
Oxalic acidt
I
COOH 3-Hydroxy
2
YOOH
isovaieric acidt
CHI CH+-OH CHJ 3
COOH
Maloic acids
dH1 dOOH 2-Furoic acidt
~Oxo-~ntanoic
\O/ c)r acid? CH
Tetrahydro
Succinic
4
COOH
2-furoic acid*
acid$
52
,
,-C-(CH ),COOH 0
t‘r
COOH
yoox f?-h COOH
Methyl succinic acid$
700” CH,TH FH2 COOH
Benzoic acidf
COON
Clutaric acid$
CyOO”
IO
m-f,),
doow
t-Methyl
~lut~ri~ acid?
FOOH
II
CH,_CH (CH,), Salicylic acidi
cioow COOH
12
Adipic acid$
yo0l-l
13
(YHA COOH 3-Methyl adipic acids
COOH &H, CH,-LH &HZ), 6OOH
14
Y. YOKOUCHIand Y. AMBE
1730 Table 1. (Confd.)
Compound
No.* 8
Formula
Pimelic acid*
Anisic acid+//
Wydroxy
benzoic acidt
17
YOOH
0 0
Phlhalic acidt,:
a 0
OH COON
18
COON
Phthalic anhydridet.5
18
Suberic acid*
COOH
19
4+Oxo-pimelic acidt
COOH
20
h-M*
dOOH
p-Hydroxy benzoic acidt
COOH
21
Te~~phfhalic acidt
YOOH
22
COOH
Characterization of polar organic3 in airborne particulate matter
1731
Table 1. (Contd.) Compound Isophthalic acidt
COOH
b
Vanillic acidt ,)I
No: 4
Formula
0
23
COOH
FOOH
24
OCH,
Azelaic acid$
3P-Dimethoxy benzoic acidt.11
Sebacic acidt
COOH (CHz), COOH COOH I
25
FOOH
21
26
(FH,), COOH Myristic acidt Undecanedioic acid*
C,,H,,COOH FOOH
28 29
(fH& COOH Pentadecanoic acidt Dodecanedioic acid*
C,,H,,COOH FOOH
30 31
(FH& COOH
Biphenyl dicarboxylic acid* HOOC @@CoDH
32
Fkrnitic acidt
C,,H,,COOH
33
Tridecanedioic acid l
YOOH
34
(FH,), , COOH Heptadecanoic acidt
C,,Cs,COOH
35
Tetradacanedioic acid l
$OOH
36
(YH,),, COOH
Y.
1732
Yo~oucmand Y. AMBE
Table 1. (Contd.) Compound
Formula
No: 8 37
Linoleic acidt
C1,H,,COOH
Oltic acid?
C,7H&XOH
38
Stearic acidt
C, ,H,,COOH
39
Pentadecanedioic acid*
YOOH
40
(FH2f13
COOH Nonadecanoic acid? Hexadecanedioic acid*
C,sH,,COOH
41
YOOH
42
(CH2h4
COOH Dehydroabje~ic acidt
Eicosanoic acidt
C,gH,,COOH
44
Heneicosanoic acid+
C20H,,COOH
45
Docosanoic acidt
C,,H,3COOH
46
Tricosanoic acid?
C2,H,,COOH
47
Tetracosanoic acidt
C&,,COOH
48
* Identification was only based on the rationalization of mass spectra. t The mass spectra corresponded fully with published reference spectra. ~~denti~~tions were performed using authentic standards. $Numbers show GC peaks of the methyl esterified compounds in Fig+ 1. 11.5See text.
attack of 0s on these olefinic acids would cause Criegce split at the ninth carbon and could produce azelaicacids by the reaction outlined in Fig. 3.This was supported by the data on mon~~xylic acids in the aerosol and soil. In spite of the similar distributions of aliphatic carboxylic acids in the aerosol and soil, oleic acid and linoleic acid were much reduced in the aerosol sample. This fact implied that these olcfinic acids had been changed or removed in the atmosphere. It is unknown whether these olefinic acids undergo ozonolysis in the gas phase or on particulates. In suburban areas, higher diacids, which are not considered to be produced pbotochemicaIIy from known pollutant gases,might be produced from the reaction of olefinic acids originated from terrestrial plants.
The presence of both phthalic acid and phthalic anhydride was determined from the W-MS analysis of the methanol extract sample prior to ~teri~~tion. Terephthalicacid and isophthalicacid were also found in the aerosol. Anisicacid identified in this study might be originally p-hydroxy benzoic acid, as hydroxy groups might also be methylated by the treatment of the sample with diazomethane. For the same reason, vanillic acid and 3,4-dimethoxy benzoic acid might result from 3.4~ihydroxy benzoic acid. Hefermyctic carboxylic acids
An unknown compound, which corresponds to the peak number 6 in Fig. 1,and amounts to iO.?/,of all the
1733
Characterization of polar organics in airborne particulate matter
.3
Hrosols
hl~rboxylic
acids
1000
800
0
Dicarboxylic acidr
0
2
4
8
8
10
12
14
Carbon
18
18
20
22
24
28
28
30
‘0
number
Fig. 2. Distributions of dicarboxylic acids and monocarboxylic acids of the aerosols. T23 : linear and aliphatic acids, = : branched-chain dicarboxylic acids, biT1: olcic acid, m: linoleic acid.
Ii 0,‘~0”
_
H-$-R H-C-@H$?COoH
+
03
-
‘o+-tc~cocm H
9 RCH
1
9
1 (oleic
acid
9 ~C-(C~~.COOH
R- =++&cw3 linoleic
acid
-
&CH-
t
v *OtZQR 4 HOOGR
R - Ct+@i * CH(CH&-C% i
+ *OO~HfCHr),COOH
1 IiOOC-fCH&COOH azelaic acid
/ Fig. 3. Formation of azelaic acid
from the ozonolysis of oleic acid and linoleic acid.
peak area in the chromatogram, was tentatively identified to be tetrahydro 2-furoic acid from the interpretation of its mass fragmentation pattern (Fig. 4). The mechanism of formation and the precursor of tetrahydro 2-furoic acid is of great interest, since it was the most abundant substance in the methanol extract of the aerosol. The presence of tetrahydrofuroic acid has not been reported before this study. One possible reason for this is that the technique of esterification, usually utilized for GC analyses of acidic compounds, might enhance evaporation of small molecules like tetrahydrofuroic acid. Mechanisms of producing tet~hydrofuroic acid are unknown, and a natural-origin compound might be a source of this acid iike azelaic acids.
Furoic acid was also found in the aerosol for the first time. One of the precursors of this acid might be furfural which is a component of diesel emission and plant vapor (Graedei, 1978). These furan-type compounds may also originate from the oxidation of isoprene (Gu et af., 1985). Keto-carboxylic acids 4-Oxo-pentanoic acid and Coxo-pimelic acid were detected in the aerosol sample. These keto-carboxyiic acids might also be produced photochemically from hydrocarbon precursors. Several other compounds were also identified to be keto-carboxylic acids from their mass spectra, although the substituted site of the carbonyl group was not specified.
1734
50
100
150
Fig. 4. Mass spectrum of the methyl ester of the most predominant acid in the highly polar fraction of the aerosols, corresponding to peak No. 6 in Fig. 1. In this study, major components of the highly polar organ& in the atmospheric aerosols were identified. They were dicarboxylic acids (C1-C16), heterocyclic acids, keto-carhoxylic acids and multifunctional aromatic acids, which were considered to he atmospheric reaction products of precursors. ft was noteworthy that olefinic atrboxytic acids, oleic acid and linole& acid may result in the formation of ditzuhoxylic acid (azclaic acid, C,) in the atmosphere. There still remain many other polar compounds which were not identi-
Gagosian R. B., Zafiriou 0. C., Peltzer E. T. and Alford J. B. (1982)Lipids in aerosols from the tropical north Pacific temporalvariability.J. geopfiys.Res. 87, 11,133-l 1,144. Graedcl T. E. (1978)C/ten&l Compoundsin the Atmosphere, p. 175.Academic press,New York. GrosjeanD, vanCauwenbcrghc IL, S&mid3.P., Kclley P. E. and Pitts, Jr. J. N. (!978) Identification of C,-C,, aliphatic dicarboxylicacids in airborne particulate m&r. &tvir. Sci.
fid
Kawamura K., Ng L-L and Kaplan I. R. (1985) Determination of organic acids (C,-C,e) in the atmosphere, motor exhausts and engine oils. Envir. Sci. Techno!. 19, 1082-1086. Lunde G., Getbcr J., Gjos N. and Lande M.-B. S. (1977) Organic micropollutants in precipitation in Norway. Atmospheric Enuiroamenr 11, 1007-1014. O’Brien R. J., Holmes J. R. and Bockian A. H. (1975) Formation of photochemical aerosol from hydrocarbons. En&r. Sci. Technot.9, 568-576. Schuetxle D., Cronn D. and Crittenden A. L. (1975) Molecular composition of secondary aerosol and its possible origin. Enutr. Sci. Technol. 9, 838-845. Simoneit 8. R. T. and Maxurck hi. A. (1982)Organic matter of the troposphere-II. Natural background of biogcnic lipid matter in aerosols over the rural western United States. Armspheric Environment 16, 2139-2159. Wauters E., Vatqaever F. Sandra P. and Verxelc M. (1979) Polar organic fraction of air particulate matter. J. CkromntogT.170, 133-l 38.
in this study. The identification
of these com-
pounds and their*precursorscould yield some important information about the environmental fate of manmade and natural-origin compounds in the atmosphere.
Ackrtowledgements-We
wish to thank Dr H. Shiraishi and Mr H. Mukai for their useful discussions. We also thank Mr H. Ito for his help in GC-MS analyses.
REFERENCES
Finlayson B. J. and Pitts, Jr. J. N. (1976)Photochemistry of the polluted troposphere. Science 192, 11l-l 19.
Technol. 12,313-317.
Gu C-f, Rynard C. M., Hendry D. G. and Mill T. (1985) Hydroxyl radical oxidation of isoprene. Enuir. Sci. Techno/. 19, 151-155.