Environ. Sci. Technol. 1990, 2 4 , 741-744
e
volumetric soil water content average pore water velocity, cm/h D apparent diffusion coefficient, cm2/h first-order degradation rate constant, h-' P linear equilibrium distribution coefficient, mL/g KD retardation factor (1 + &D/d) R X distance, cm t time, h duration of input pulse, h to Registry No. Simazine, 122-34-9.
(14) van Genuchten, M. Th.; Davidson, J. M.; Wierenga, P. J. Soil Sci. SOC.Am. R o c . 1974, 38, 29. (15) Rao, P. S. C.; Davidson, J. M.; Jessup, R. E.; Selim, H. M. Soil Sci. SOC.Am. J. 1979, 43, 22. (16) Selim, H. M.; Davidson, J. M.; Mansell, R. S. Proceedings,
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M. Th.; Wierenga, P. J.; Davidson, J. M.; Nielsen, D. R. Water Resour. Res. 1983, 19, 691. (19) Nkedi-Kizza,P.; Biggar, J. W.; Selim, H. M.; van Genuchten, M. Th.; Wierenga, P. J.; Davidson, J. M.; Nielsen, D. R. Water Resour. Res. 1984,20, 1123. (20) Spurlock,F. C. M.S. Thesis, University of California,Davis,
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Summer Computer Simulation Conference;American Institute of Chemical Engineers: Washington, DC, 1976; p 444. (17) van Genuchten, M. Th.; Wierenga, P. J. Soil Sci. SOC.Am. J . 1976, 40, 473. (18) Nkedi-Kizza,P.; Biggar, J. W.; Selim,H. M.; van Genuchten,
735. (2) Chiou, C. T.; Malcolm, R. L.; Brinton, T. I.; Kile, D. E. Environ. Sci. Technol. 1986, 20, 502. (3) Hassett, J. P.; Anderson, M. A. Environ. Sci. Technol. 1979, 13, 1526. (4) Hassett, J. P.; Anderson, M. A. Water Res. 1982,16,681. (5) Ballard, T. M. Soil Sci. SOC.Am. Proc. 1971, 35, 145. (6) Khan, S. H. Environ. Sci. Technol. 1974, 8, 236. (7) Bowman, B. T. Soil Sci. SOC.Am. J. 1978, 42, 441. (8) Hayes, M. B. H.; Stacey, M.; Thompson, J. M. In Isotopes
1988. (21) Lyman, W. J. In Handbook of Chemical Property Esti-
mation Methods; Lyman, W. J., Reehl, W. F., Rosenblatt, D. H., Eds.; McGraw-Hill; New York, 1982; Chapter 4. (22) Rao, P. S. C.; Davidson, J. M. In Environmental Zmpact of Nonpoint Source Pollution; Overcash, M. R., Davidson,
J. M., Eds.; Ann Arbor Science: Ann Arbor, MI, 1982; pp
and Radiation in Soil Organic-MatterStudies. Proceedings o f a Symposium. IAEA, FAO, and ISSS: Vienna, 1968;
23-67. (23) Hassett, J. J.; W. L. Banwart. In Reactions and Movement
pp 75-94. (9) Wijayaratne, R. D.; Means, J. C. Environ. Sci. Technol.
of Organic Chemicals in Soils; Sawhney,B. L., Brown, K., Eds.; SSSA Special Publication 22; American Society of Agronomy and Soil Science Society of America: Madison, WI, 1989; Chapter 2. (24) Pignatello, J. J. In Reactions and Movement of Organic Chemicals in Soils; Sawhney,B. L., Brown, K., Eds.; SSSA Special Publication 22; American Society of Agronomy and Soil Science Society of America: Madison, WI, 1989; Chapter 3. (25) Karickhoff, S. W. J. Hydraul. Eng. 1984, 110, 707.
1984, 18, 121.
(10) Madhun, Y. A.; Young, J. L.; Freed, V. H. Environ. Qual. 1986, 15, 64. (11) Schnitzer, M. In Methods of Soil Analysis, 2nd ed.; Page,
A. L., Miller, R. H., Keeney, D. R., Eds.; American Society of Agronomy and Soil Science Society of America: Madison, WI, 1982; p 590. (12) Chen, Y.; Senesi, N.; Schnitzer, M. Soil Sci. SOC.Am. J . 1977. 41. 352. (13) Parker, 'J. C.; van Genuchten, M. Th. Determining
Transport Parameters From Laboratory and Field Tracer Experiments; Virginia Agricultural Experiment Station Bulletin 84-3, 1984.
Received for review March 24,1989. Revised manuscript received November 6, 1989. Accepted January 22,1990.
Characterization of Carbonaceous Aerosols in the Nagoya Urban Area. 1. Elemental and Organic Carbon Concentrations and the Origin of Organic Aerosols Satoshi Kadowaki Aichi Environmental Research Center, 7-6, Nagare, Tsuji-machi, Kita-ku, Nagoya 462, Japan
Concentrations of elemental carbon (EC) and organic carbon (OC) were determined in air samples collected in the Nagoya urban area by high-volume samplers for a 24-h duration. EC and OC comprised about 12 and 15% of the total suspended particulate mass, respectively. It was found that organic aerosols and EC are major components of Nagoya urban aerosols. The concentration ratio of total carbon (TC)to EC showed little seasonal de ndence. The TC to EC ratio did not change under the ide photochemical activity conditions indicated by the o ant level, while a good correlation was obtained between the concentration of OC and that of carbon monoxide, an indicator of primary combustion products. These results suggest, with respect to the origin of organic aerosols in the Nagoya urban area, that primary organic aerosols are the principal contributor to organic aerosols throughout the year, and that secondary organic aerosols hardly contribute to the total organic aerosol mass.
%
Introduction
It has become apparent in recent years that ambient 0013-936X/90/0924-0741$02.50/0
aerosols, especially in urban areas, contain a significant fraction of carbonaceous material, which is mainly comprised of organic compounds and elemental carbon (EC). The latter is sometimes referred to as black carbon. Carbonaceous aerosols in urban areas are directly emitted from stationary and mobile sources, and moreover, several studies suggest that most of the organic aerosols are secondary aerosols formed in the atmosphere by photochemical reactions of gaseous hydrocarbon precursors (1-4). EC has optical and chemically catalytic properties, so that it plays important roles in the visibility reduction (5, 6 ) ,climate modification (7,8),and formation processes of secondary aerosols in the atmosphere (9, IO). On the other hand, organic aerosols are important in health effects because of the carcinogenic activity of the extracts in laboratory animals (11). The ratio of primary to secondary organic aerosols is also important in the development of strategies for control of aerosol carbon air quality. Despite these important characteristics, measurements of ambient concentrations of carbonaceous aerosols are sparse in comparison with other species such as sulfate and
0 1990 American Chemical Society
Environ. Sci. Technol., Vol. 24, No. 5, 1990 741
Table I. Average Concentrations (pg/mS)of Total Suspended Particulate (TSP), Total Carbon (TC), Elemental Carbon (EC), and Organic Carbon (OC) in the Nagoya Urban Area, 1984-1986
oc
season
no. of samples
mean"
TSP SDb
range
mean"
TC SDb
range
meana
EC SDb
range
mean"
SDb
range
spring summer autumn winter
13 15 15 12
114 87.2 119 102
31.4 16.6 37.4 53.4
70.5-160 63.6-131 68.5-187 30.9-195
25.9 22.4 39.9 28.8
4.43 4.07 15.2 15.7
16.9-32.6 22.4-31.0 17.3-64.0 12.5-64.8
10.7 9.77 17.9 13.7
2.07 2.08 7.50 8.56
6.1-13.0 7.2-13.6 6.6-30.9 5.3-34.4
15.2 12.6 22.0 15.1
3.14 2.21 7.81 7.68
10.8-20.7 9.8-17.5 10.7-34.1 7.2-30.4
Arithmetic mean. Standard deviation.
nitrate. Recent advances, however, in analytical measurement techniques have permitted routine determination of EC and organic carbon (OC) concentrations in ambient aerosol samples. Application of new techniques for carbon analysis is making up for the lack of data on ambient carbonaceous aerosols, though a few problems remain in the techniques (12). The present paper is the first of a series to characterize carbonaceous aerosols in the Nagoya urban area. In this study, concentration measurements were made for EC, OC, and gaseous pollutants of oxidant and carbon monoxide from 1984 to 1986. From the results, the ratios of EC and OC to total suspended particulate (TSP) and the contribution of secondary organics to organic aerosols in the Nagoya urban area were discussed.
Experimental Section Aerosol samples were collected on quartz fiber filters (8 X 10 in. Palfflex 2500 QAST) in standard high-volume samplers (Model 120, Kimoto Electronics Corp.) a t the Aichi Environmental Research Center. The site, located 15 km north of the coastal heavy industry area and - 5 km north of the central business district, receives both primary and secondary aerosols (13)and high oxidant air mass during photochemical smog episodes (14). Aerosol sampling was carried out between February 1984 and November 1986. The sampling period was typically for a 24-h duration from 8 a.m. to 8 a.m. Before aerosol sampling, filters were preheated a t 600 "C for 3 h in air to reduce the carbon blank. Carbon analyses of the filter samples were generally conducted within 1week of sample collection. Until analyzed for carbon, filter samples were stored in a freezer in order to prevent loss of OC. Concentrations of EC and OC on sample filters were measured by the method previously described (15). Two strips (3 X 70 mm) were cut out from the filter by a punch. One strip was analyzed directly for total carbon (TC) with a CHN analyzer (Model MT-3, Yanagimoto Corp.). A second strip was placed in a quartz tube, which was constantly supplied with helium and heated a t 900 OC, for 2 min to remove as much of the OC as possible and to minimize charring. The residual carbon on the second strip was then analyzed by the CHN analyzer to determine EC. OC content was calculated as the difference between TC and EC. The coefficient of variation for carbon by the CHN analyzer was better than 2%. The detection limits of TC, EC, and OC were about 1.5, 0.5, and 1.0 pg/m3, respectively, for a sample volume of 2000 m3, based on the average filter blank plus 2 times the mean standard deviation of the filter blanks. Carbonate carbon in samples was not considered in this procedure because the content of carbonate carbon in urban aerosols is very small as compared with those of EC and OC (16, 17). Oxidant and CO were monitored with a neutral-buffered KI solution spectroscopic analyzer (Model GXH-71M-l(S),
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Environ. Sci. Technol., Vol. 24, No. 5, 1990
Table 11. Average Concentration Ratios of Carbonaceous Aerosols to TSP and Composition of Carbonaceous Aerosols in the Nagoya Urban Area, 1984-1986"
TC/TSP EC/TSP OC/TSP
OC/TC
season
(%I
(%I
(%)
TC/EC
(%)
spring summer autumn winter annual av
22.7 25.7 33.5 28.2 27.5
9.4 11.2 15.0 13.4 12.2
13.3 14.4 18.5 14.8 15.3
2.4 2.3 2.2 2.1 2.3
59 56 55 52 56
"TSP. TC. EC. and OC are described in Table I.
Denki Kagaku Keiki Co. Ltd.) and a NDIR CO analyzer (APMA-2000, Horiba Ltd.), respectively. A UV absorption ozone analyzer (Model EG-2001, Ebara Jitsugyo Corp.) was also used to check oxidant concentrations measured by the oxidant analyzer.
Results and Discussion Seasonal concentration data for TSP, TC, EC, and OC during the field measurements are summarized in Table I. The seasonal average concentrations ranged from about 90 to 120 pg/m3 for TSP and from about 20 to 40 pg/m3 for TC. The ranges of those for EC and OC were 10-18 and 13-22 pg/m3, respectively. Both the concentrations of EC and OC had a tendency to increase in autumn months. The highest seasonal average concentration of EC, 17.9 pg/m3, was observed in the autumn and was roughly 2 times higher than the minimum of 9.77 pg/m3, which occurred in the summer. Identical behavior was observed for OC. The maximum and minimum OC concentrations were 22.0 and 12.6 pg/m3, respectively. These seasonal variations of OC and EC in the Nagoya urban area were consistent with those in other urban areas in Japan (18). The finding that OC concentration did not increase during the summer high photochemical activity season is of great interest from the viewpoint of the contribution of secondary organic aerosols to OC concentration. Table I1 shows the concentration ratios of carbonaceous aerosols to TSP and the carbonaceous aerosol ratios of TC/EC and OC/TC. The annual average of the TC to TSP ratio was 27.5%, which showed that carbonaceous aerosols account for approximately 30% of TSP mass loadings and they are one of the most abundant components of Nagoya urban aerosols along with soil particles (19) and sulfate and nitrate (20). The annual average ratios of EC/TSP and OC/TSP were 12.2 and 15.3%, respectively. The seasonal variations of these ratios, which were maximum in the autumn, were similar to those of the concentrations shown in Table I. It is, hence, concluded that nonphotochemical smog, frequently observed in the Nagoya urban area from the autumn to the beginning of the winter, is mainly composed of carbonaceous aerosols. With regard to atmospheric EC, it is generally accepted that EC is not formed in the atmosphere by reactions
LO
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II
I
c 30-
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c
0
2 1.0
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10-
I
C
0
0
-
0
I
I
I
I
I
I
I
I
10 20 30 Concentration of elemental carbon i!4/m31
Flgure 1. Scatter diagram of elemental carbon and organic carbon concentrations for 24-h samples collected in the Nagoya urban area, 1984-1986. V,spring; 0,summer; A,autumn; 0,winter. The solid line is a least-squares fit of the data.
involving gaseous precursors. It is produced only in combustion processes and is a primary pollutant. In contrast to EC, OC (i.e., organic aerosol) is not only directly emitted from sources, but also can be produced by atmospheric reactions from gaseous precursors. Primary organic aerosols should be emitted from sources at a nearly constant rate for EC. For example, Cass et al. (16) estimated the ratio of TC/EC in primary aerosol emissions to be -3.2 averaged over all sources in Los Angeles, and the overall ratio of EC/TC estimated by Wolff et al. (21) was 0.37 (2.7 as the ratio of TC/EC) for primary emissions in Denver. Therefore, the concentration ratios of carbonaceous aerosols, e.g., TC/EC, are useful as an indicator of secondary organic aerosol production. Several investigators reported from the results of selective solvent extraction of organics ( 1 , 4 ) , thermograms of aerosols ( 2 ) ,and the concentration ratio of OC/EC (3) that photochemical gas-to-particle conversion plays an important role in the secondary organic aerosol production, and that the greater part of organic aerosols is secondary during photochemical smog season. However, Rosen et al. (22),Wolff et al. (23),and Gundel and Novakov (24) have indicated that there is no relationship between photochemical activity indicated by ozone level and secondary organic aerosol production. Gray et al. (25, 26) also have suggested that secondary organic aerosols are not the overwhelming contributor to organic aerosols in Los Angeles on the basis of the field data in which the concentration ratio of TC/EC in Los Angeles showed little seasonal dependence and averaged 2.6 over an annual cycle. In Table 11, the seasonal averages of the composition of carbonaceous aerosols in the Nagoya urban area are listed in two forms as TC/EC and OC/TC. The seasonal averages of TC/EC ranged from 2.1 to 2.4, and the annual average was 2.3. If a large fraction of organic aerosols in the Nagoya urban area is contributed by photochemically produced secondary organic aerosols, a seasonal peak in the TC to EC ratio should be observed during the summer photochemical season, reflecting enhanced secondary organic aerosol production. There was, however, no significant seasonal variation in the ratio of TC to EC. Figure 1 is a scatter plot for the concentration of EC against that of OC in 24-h samples. The least-squares fit of the data ( n = 55) yields a correlation coefficient, r, of 0.904. This excellent EC-OC correlation also supports that
I
I
1
50 100 150 Daily maximum oxidant concentration Ippbl
Figure 2. Relationship between the daily maximum oxidant concentration and the concentration ratio of total carbon to elemental carbon in the Nagoya urban area, 1984-1986. Symbols are as described in Figure 1.
y = l L 7x +1 29 r.0.905 1 n-531
I
0’
I
I
I
I
1.0 2.0 I Avemge carbon monoxide concentration bpmi
Flgure 3. Relationship between the average 24-h carbon monoxMe concentration and the organic carbon concentration in 24-h samples collected in the Nagoya urban area, 1984-1986. Symbols are as described in Figure 1. The solid line is a least-squares fit of the data.
the composition of carbonaceous aerosols in the Nagoya urban area is almost constant independently of season. In order to further clarify the contribution of photochemical processes to secondary organic aerosol production, the relationship between the concentration ratio of TC/EC and the daily maximum oxidant concentration, which is viewed as an indicator of the photochemical activity, is shown in Figure 2. As seen in Figure 2, the ratio of TC to EC was approximately constant under the wide photochemical activity conditions ranging in daily maximum oxidant concentration from about 10 to 150 ppb. The results in Table I1 and Figures 1 and 2 indicate that gasto-particle conversion by photochemical reactions hardly contributes to the total organic aerosols in the Nagoya urban area, though secondary organic aerosols may be present. In contrast with oxidant concentration, CO concentration can be used as an indicator of the primary combustion products. Figure 3 shows the relationship between the concentration of OC and the 24-h average concentration of CO simultaneously monitored. Good correlation was found between the concentration of OC and that of CO, with a high correlation coefficient of 0.905 (n = 53). It is, therefore, appropriate to consider that primary organic aerosols are the principal contributor to organic Environ. Sci. Technol., Val. 24, No. 5, 1990 743
aerosols in the Nagoya urban area throughout the year, and that secondary organic aerosols scarcely contribute to the total organic aerosol mass, whether secondary organic aerosols are produced by photochemical processes or not.
S u m m a r y and Conclusions Concentrations of EC and OC were determined for 24-h high-volume filter samples collected in the Nagoya urban area from 1984 to 1986. Carbonaceous aerosols accounted for approximately 30% of TSP mass loadings. It was found that organic aerosols and EC are major components of Nagoya urban aerosols. The concentration ratio of TC/EC showed little seasonal dependence. The TC to EC ratio did not change under the wide photochemical activity conditions indicated by daily maximum oxidant concentration, while the concentration of OC correlated closely with that of CO, an indicator of primary combustion products. These results suggest that organic aerosols in the Nagoya urban area are primary in origin, and that secondary organic aerosols hardly contribute to the organic aerosols. However, in order to conclude exactly the origin of organic aerosols in the Nagoya urban area, other approach is required in addition to measurements of particulate carbon concentration. Acknowledgments I thank Dr. N. Naruse, Director of Aichi Environmental Research Center, for his continual support and interest. I also appreciate the help of M. Ando in data collection by computer. Registry No. C, 7440-44-0.
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Received for reuiew March 17,1989. Revised manuscript received September 7, 1989. Accepted December 29, 1989.
