Substantial concentrations of graphitic carbon and its associated large optical absorption coefficient are observed in the Arctic. The graphitic content shows a dramatic increase from late fall to early spring, reaching levels that can be comparable to those found in urban environments

Bodhaine, B. A.

Novakov, T.

Rosen, H.

UNT Digital Library

Submitted to Atmospheric Environment SOOT IN THE ARCTIC H. Rosen, T. Novakov, and B.A. Bodhaine October 1980 TWO~WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call ;1!1 Tech. Info. Division, Ext. 6782. IIJI' LBL-11648 c_.. Pre print bor tory NT Prepared for the U.S. Department of Energy under Contract W-7405-ENG-48 --DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. 1 SOOT IN THE ARCTIC H. Rosen and T. Novakov Lawrence Berkeley Laboratory University of California Berkeley, California 94720 B.A. Bodhaine NOAA-GMCC Air Resources Laboratory Boulder, Colorado 80303 Abstract LBL-11648 Substantial concentrations of graphitic carbon and its associated large optical absorption coefficient are observed in the Arctic. The graphitic content shows a dramatic increase from late fall to early spring, reaching levels that can be comparable to those found in urban environments. 2 LBL-11648 Recent studies in the Arctic 1•2 show the presence of large aerosol concentrations which significantly affect optical transfer through the atmos-phere and lead to the phenomenon of Arctic haze, which was first reported by Mitchell. 3 In particular, the observation of substantial concentrations of particulate sulfur and vanadium at the NOAA-GMCC sampling station near Barrow, Alaska, has attracted considerable attention. 1•2 Questions have been raised as to the anthropogenic character, sources, and climatic impacts of these aerosols. In order to gain a better understanding of these issues, a study of the physical and chemical properties of the carbonaceous aerosol at Barrow was initiated in October, 1979. Recent studies of the urban aerosol indicate the presence of substantial graphitic carbon concentrations. These graphitic species- identified by a variety of modern analytical techniques (Raman spectroscopy, 4 photoacoustic spectroscopy, 5 thermal analysis, 6 etc.)- are very effective absorbers of visible radiation and are responsible for the high optical absorption coeffi-cients which have recently been observed in urban air. 7•8 The impacts of these highly absorbing particles on a regional or global scale have not been assessed so far, but they could be important, especially over regions with a high surface albedo like the polar icecaps. Furthermore, graphitic carbon can only be produced from combustion processes, and therefore it can offer a very attractive and convenient tracer for anthropogenic activity. An aerosol sampler was constructed to collect parallel 47-mm quartz fiber and Millipore filter samples at a flow rate of~ 1.5 cfm. The sampler had two chambers - a lower chamber which contained the pumps and an upper chamber for collecting the aerosol samples. The upper chamber was warmed by several thermostatically controlled heatlamps, while temperature control in the lower chamber was achieved by using a thermostatically controlled fan and 3 LBL-11648 heatlamps. The exhaust of the pumps was vented below the sampling platform. To minimize local contamination, the aerosol sampler was controlled by a wind 1 sensor which was built by the University of Rhode Island group. This allowed samples to be collected only when the wind was from the clean air sector at Barrow, between 0° North and 130° Southeast. Results obtained with and without the wind controller suggest that there is no significant influence from local sources. Approximately 50 filter pairs have been collected at sampling time intervals ranging from 2 days to 1 week. The quartz filters were used to 9 determine the total carbon content of the aerosol by a combustion method, and the Millipore substrate was used to determine the optical absorptio~ coeffi-cient of the aerosol by the LBL laser transmission method described elsewhere. 4 •5 • The absorption coefficients reported here are consistent with the optical constants of graphitic carbon and are expected to have an accuracy of better than a factor of 2. The Millipore substrate was also analyzed by the X-ray fluorescence technique to determine the concentration of elements with Z > 11. The quartz blanks had a carbon loading of< .5 JJg/cm2 , while typical filter deposits corresponded to 15 JJg/cm2. Selected filters have been analyzed by Raman spectroscopy, thermal analysis, and solvent extraction techniques. The results of these analyses are described below. Raman spectroscopy is a highly selective method of analysis which has been used to identify large concentrations of graphitic carbon in urban particulates. 4 This technique has been applied to the analysis of 5everal samples collected at Barrow. The experimental arrangement and methods are described elsewhere. 4 The results are shown in Fig. 1, where the spectrum of an Arctic sample collected in December 1979 is compared to that of urban particulates, various source emissions, and carbon black. All these spectra show the presence of two intense Raman modes located at 1350 and 1600 cm- 1 , which have been identified as being d 10 ue to phonons propagating with graphitic planes. This result shows that graphitic structures similar to carbon black and due to combustion processes 8 4 LBL-11648 are present in the Arctic aerosol. Furthermore, the large intensity in these modes indicates that, just as in urban samples, the graphitic structures repre-sent a major component of the aerosol. The filters collected at Barrow from fall through late spring have a grey or black appearance similar to that found for urban particulates. For the urban samples, this optically absorbing component has been identified as graphitic 4 carbon. Preliminary measurements on a limited number of samples show that the optically absorbing species in the Arctic has a 1/A wavelength dependence, is insoluble in a wide range of solvents, and has a high temperature stability with an oxidation threshold of approximately 500°C. These results are consistent with the properties of graphitic carbon and strongly suggest that indeed the optically absorbing species at Barrow is graphitic in nature. The seasonal variation of the optical absorptivity (or graphitic carbon con-centration) of the Barrow aerosol is shown in Fig. 2. The absorption coefficient changes by more than an order of magnitude from mid-October to early January and remains at a relatively high level throughout most of February, March, and April. It decreases substantially in May. The magnitude of the absorption coefficient during the winter and spring is comparable to that found in urban environments (Table I) (i.e., the peak values in February are only about a factor of 10 less than the average absorption coefficients in New York City and a factor of 3 less than those found in Berkeley, California, and Denver, Colorado). This absorption coefficient is large enough to produce significant optical effects. For example, an absorption coefficient of 5 x 10-6 m-l extended over a pathlength of 10 km would produce an optical thickness of .OS. This would be a large perturbation on the transfer of optical radiation through the atmosphere when the sun's irradiance is at a high level, as it is during part of these pollution episodes. In order to assess the importance of these 5 LBL-11648 effects, more detailed measurements of the seasonal variation in the optical properties (visible and infrared) and the vertical and horizontal extent of the aerosols need to be determined. The pollution episodes observed at Barrow are not a local phenomenon but appear to be areawide with similar seasonal variations occurring at widely spaced sites across the Arctic. 11 •12 This is illustrated in Fig. 3, where a comparison of the monthly variations in the blackness of the filter deposits collected at Barrow and Mould Bay, Canada, are shown. (The samples from Mould Bay were provided by Dr. L.A. Barrie and Dr. P. Hoff of the Canadian Atmospheric Environment Service.) These sampling stations are widely separated, yet the initial onset and duration of the episodes observed at these two sites are almost identical. Using the optical constants of graphitic carbon determined from our urban d . 13 k . f h stu 1es, we can rna e an est1mate o t e graphitic carbon concentration at Barrow. These results are shown in Fig. 4, where we plot the graphitic carbon concentration as a fraction of the total carbon content of the aerosol for various periods of time during the year. The results show a strong enrichment of the graphitic fraction of the carbonaceous aerosol from early to late winter. The concentration of graphitic carbon in late February is almost 40% of the carbonaceous mass. Remarkably, this percentage is higher than that found in 14 urban centers like New York City and Los Angeles. After its peak in February, the fraction of graphitic carbon seems to level off to a value which is more typical of those found in urban environments. The interpretation of these interesting features in terms of transport, atmospheric chemistry, and deposition processes is complicated and will have to await more detailed analyses and further measurements. In summary, these observations indicate that large graphitic concentrations 6 LBL-11648 can develop at remote locations. If one ignores the possible contribution of natural burning processes (e.g., forest fires), which is expected to be small during these times of year in the northern hemisphere, this component can be attributed directly to the burning of fossil fuels. The source and the climatic effects of these highly absorbing species are uncertain and will have to await more systematic measurements and careful modelling. Acknowledgment This work was supported by NOAA, Air Resources Laboratory, and by DOE, co2 and Climate Program. The authors would also like to acknowledge stimula-ting and helpful discussions with Lester Machta, NOAA, and with Michael MacCracken, Lawrence Livermore Laboratory. This work was supported by the Energy and Environment Division, Atmospheric Aerosol Research Group of the U.S. Department of Energy under Contract W-7405-ENG-48. 7 LBL-11648 References 1. K.A. Rahn and R.J. McCaffrey, "On the origin and transport of the winter Arctic aerosol," in Proceedings, Conference on Aerosols: Anthropogenic and Natural - Sources and Transport, New York Academy of Sciences, New York City, 9-12 January 1979 (in press). 2. G.E. Shaw and K. Stamnes, "Arctic haze: Perturbation of the polar radia-tion budget," in Proceedings, Conference on Aerosols: Anthropogenic and Natural - Sources and Transport, New York Academy of Sciences, New York City, 9-12 January 1979 (in press). 3. M. Mitchell, "Visual range in the polar regions with particular reference to the Alaskan Arctic," J. Atmos. Terr. Phys., Special Supplement, 195 (1956). 4. H. Rosen, A.D.A. Hansen, L. Gundel, and T. Novakov, "Identification of the optically absorbing component in urban aerosols," Appl. Opt. !:2_, 3859 (1978). 5. Z. Yasa, N.M. Amer, H. Rosen, A.D.A. Hansen, and T. Novakov, "Photoacoustic investigation of urban aerosol particles," Appl. Opt. l!• 2528 (1979). 6. R. Dod et al., "Application of thermal analysis to the characterization of nitrogenous aerosol species," LBL-10735, Ch. 8 from LBL Energy and Environment Division Annual Report, 1979 (1980). 7. R.E. Weiss, A.P. Waggoner, R. Charlson, D.L. Thorsell, J.S. Hall, and L.A. Riley, "Studies of the optical, physical, and chemical properties of light absorbing aerosols," in Proceedings, Conference on Carbonaceous Particles in the Atmosphere, Lawrence Berkeley Laboratory, Report LBL-9037 (1979), p. 257. 8. M. Sadler, R.J. Charlson, H. Rosen, and T. Novakov, "An intercomparison of the integrating plate and the laser transmission methods for determination 8 LBL-11648 of aerosol absorption coefficients," Report LBL-11176 (1980); submitted to Atmos. Environ. 9. P.K. Mueller, R.W. Mosley, and L.B. Pierce, "Carbonate and non-carbonate carbon in atmospheric particulates," Second International Clean Air Congress, Proceedings (New York, Academic Press, 1971). 10. F. Tuinstra and J.L. Koenig, "Raman spectrum of graphite," J. Chern. Phys. 53, 1126 (1970). 11. L.A. Barrie et al., paper presented at Second Symposium on Arctic Air Chemistry, Kingston, Rhode Island, 6-8 May 1980. 12. B. Ottar et al., paper presented at Second Symposium on Arctic Air Chemistry, Kingston, Rhode Island, 6-8 May 1980. 13. A.D.A. Hansen et al., "The use of an optical attenuation technique to estimate the carbonaceous component of urban aerosols," LBL-10735, Chap. 8 from LBL Energy and Environment Division Annual Report, 1979 (1980). 14. H. Rosen, A.D.A. Hansen, R.L. Dod, and T. Novakov, "Soot in urban atmospheres: Determination by an optical absorption technique," Science 208, 741 (1980). Table I. Number of Site Date samples Barrow, Alaska 12/79-4/80 33 Argonne, Illinois 1/79-3/80 438 Gaithersburg, Maryland 1/79-3/80 381 Denver, Colorado 11/78-5/79 141 Anaheim, California 8/77-1/SG 852 Fremont, California 7/77-3/80 924 Berkeley, California 6/77-4/80 998 New York, New York 11/78-4/80 439 aCalculated from optical constants in Ref. 13. Average absorption coefficient x 105 Average total (m-1) carbon (llgfm3) .4 1.2 2.8 8.1 2.1 6.1 2.4 9.8 4.9 16.6 3.4 12.0 2.1 6. 7 6.4 15.2 Average graphitic carbon as percent of total carbona 24 . 22 22 16 19 18 20 27 'D t-' co t-' I ....... ....... (J\ -""' co 10 LBL-11648 Figure Captions Figure 1. Raman spectrum of an Arctic sample compared to those of urban particulates, various source emissions, carbon black, and polycrystalline graphite. Figure 2. Seasonal variations in the optical absorption coefficient in m-l at Barrow from October 1979 to May 1980. Figure 3. A comparison between the seasonal variation in the blackness of filter deposits collected at Barrow, Alaska, and Mould Bay, Canada, in 1979 and 1980. Mould Bay samples were provided by L.A. Barrie and P. Hoff of the Canadian Atmospheric Environment Service. Figure 4. Seasonal variation of graphitic carbon as a percentage of the total carbon content of the aerosol at Barrow from October 1979 to May 1980. These values are compared to the average values obtained in New York City and Los Angeles. 11 LBL-11648 I I ' •• • • Arctic ... . haze • ' . • • . ,• ~ . . . • • ' I •e/• e:?:J~~o:~~~ . ··I'Yo~.t•• .. • ~.~. •,e •. eo~. St. Louis, /' tli ssouri . . .. · . ... .,..":"",..,..,..,.~.,•:.,.,. .... .,o.,••"ao"".,".,.,.,"•"., ............ o.." "<~o-• .. tft<>"~.,: .............. rl,."· .. .. """'"· .... .. ..... . . ; ~ ... Car : ' ... . . .1' \~ : ~./ ~ ·• "' ;, ~,.,.· '~? .............. ._ .:: .. • ~\\., :~· \ Diesel .,. a"•-1' ;, ./ oft-,. 'w-.,.:~ .. . . ~~ ·':.I~..,.,~"'::.~.:, ...... ,.. . ....:,:.....1'!:: ; ~ / .. ' . , '· . : Carbon .• \ r black ' ~ / v ·"""' . ~ ... ""-: .. Graphite I .. t ! . ' 'o' \,~ ..... ..... ..._.........,.,_....... ~N\,~.....,..4!1 1000 1200 1400 1600 1800 Frequency shift (em-') XBL 767-3091 A Figure 1 9 -8 <.0 I 0 X 7 .c 0 ...0 -- 6 c Q) u ..;: 5 '+-Q) 0 u c 4 0 -e-3 0 en ...0 <( 2 July Barrow ( 1979-1980) o ooo 0 0 0 0 Ooo 0 0 0 0 0 0 0 00 oo 0 0 00 0 0 0 00 0 0 0 & 0 0 0 0 Oo 0 0 00 Aug. Sept. Oct. Nov. Dec. June Feb. March April May June XBLSOI0-4418 Figure 2 !-' N t'""' Ct:l t'""' i !-' ....... 0\ .j:>. 00 13 LBL-11648 ~ Barrow (1979-1980) ]\I ;z ......... ......... -(/) -c :l ~ J ~ b. E -..0 b. c -(/) (/) (I) c Mould Bay (1979-1980) ~ .::s:. () c -m 10:4 /~ ~ ~ HH j July Aug. Sept. Oct. Nov. Dec. Jan. Feb. March Apr. May June XBL 8010-4420 Figure 3 -...,_ Q) 0 ,_ Q) 40 c.. 30 -0 ..c ,_ 0 0 0 ...,_ 20 .s::::. c.. 0 ,_ (!) 10 o- Biweekly overages Borrow 1979-1980 --New York "''i Los Angeles Oct Nov Dec Jon eb Mar Apr May June XBL 809-2013 Figure 4 ...... ..,.. t""' t:l:! t""' I ...... ....... 0\ ..,.. 00 

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