Elemental carbon, aerosols

Clarke, A. D., Weiss, R. E., and Charlson, R. J. (1984) Elemental carbon aerosols in the urban, rural and remote-marine troposphere and in the stratosphere. Interferences from light absorption data and consequences regarding radiative transfer, Sci. Total Environ., 36, 97-102. 

McMurry, P. H., and Zhang, X. Q. (1989) Size distributions of ambient organic and elemental carbon. Aerosol Sci. TechnoL, 10, 430-437. 

Whatever the process of external combustion, it has been shown that the amount of harmfid emission can be minimized by carefid control of the fuel mixtures and the burning conditions (e.g. the combustion temperature). Flames near the sooting limit (i.e. those from fuel-rich mixtures whose conditions just define the onset of the release elemental carbon aerosol) exhibit a large number of intermediate species, such as H2 and CO, rather than H2O and CO2. Furthermore, depending on the fuel, incomplete combustion will lead to the likely production of a variety of hydrocarbons or aromatic compounds. 

Organic compounds are a major constituent of the FPM at all sites. The major sources of OC are combustion and atmospheric reactions involving gaseous VOCs. As is the case with VOCs, there are hundreds of different OC compounds in the atmosphere. A minor but ubiquitous aerosol constituent is elemental carbon. EC is the nonorganic, black constituent of soot. Combustion and pyrolysis are the only processes that produce EC, and diesel engines and wood burning are the most significant sources. 

More complex substances, however, showed higher degrees of pyrolytic conversion. In aerosol samples collected from the combustion of distillate and residiaal oil, 31 and 25% respectively of the organic carbon underwent pyrolytic conversion to elemental carbon. Lesser amounts of conversion were observed for leaded and unleaded auto exhaust samples, and no conversion occurred in a diesel truck exhaust sample. Biological samples also showed large degrees of conversion e.g., 45% of the carbon associated with wood fiber was pyrolytically converted to elemental carbon. 

The carbon analyzer has been used to analyze filters from 42 urban sites and 22 non-urban sites in the United States. These filters were obtained from the National Air Surveillance Network (NASN) filter bank for 1975. Carbon concentrations and mass fractions for Detroit, Michigan, are shown in Figures 5 and 6. Both the organic and elemental carbon concentrations are highly variable, and no seasonal trends are apparent. For this site elemental carbon constituted 38% of total aerosol carbon. Typical values for other sites ranged between 35 and 55%. 

Johnson, R.L. Huntzlcker, J.J. "Analysis of volatilizable and elemental carbon in ambient aerosols", in "Proceedings Carbonaceous Particles in the Atmosphere", T. Novakov, Ed., Lawrence Berkeley Laboratory, Berkeley, California, June 1979, 10-13. 

Delumyea, R.G. Chu, L.-C. Macias, E.S. "Determination of elemental carbon component of soot in ambient aerosol samples", Atmos. Environ., 1980, 14, 647-652. 

To verify this hypothesis, low volume samplers have been operated in parallel with the air pollution control district s Km samplers. The samples collected were analyzed optically for elemental carbon and by the Gamma Ray Analysis of Light Elements (GRALE) technique for total carbon. These data were used to assess the concentration of elemental and total carbon aerosols present during the winter months in Los Angeles. It was established that the Km samplers can be calibrated to read elemental carbon concentrations. This calibration can be used to reconstruct historical elemental carbon levels at seven sites in Los Angeles. 

Filter substrates were chosen that were suited for subsequent determinations of aerosol mass, total carbon, elemental carbon, trace metals and aerosol light absorption coefficient The three filter assemblies contained, a 47 mm Pallflex Tissuquartz filter (2500 QAO), a 47 mm Nuclepore polycarbonate filter (0.40 ym pore size) and a 13 mm Pallflex Tissuquartz filter (2500 QAO). 

Graphitic carbon particles are thought to be the most abundant light-absorbing aerosol species in the atmosphere (2,). Comparison of elemental carbon concentrations from the present study to measurements of b. is presented in Figure 5. A regression line drawn through those data has the equation ... 

An upper limit to the absorption efficiency of the elemental carbon particles sampled can be obtained if it is assumed that all aerosol light absorption is due to elemental carbon. In that case the specific absorption from the slope of the line in Figure 5 is about 11.9 0.9 m g. That value is higher than would be... 

If the blackness of the particulate matter collected on a filter is due to the graphitic carbon content of the sample, then the Km unit should convert to ambient elemental carbon concentrations. The form of that translation is apparent from the definition of the Km unit. Elemental carbon concentration measurements made by laboratory reflactometers calibrated against heated butane soot standards show that elemental carbon concentrations are linearly related to the log of the reflectance ratio R /R. Aerosol loadings stated in Km units should be directly proportional to elemental carbon concentrations sampled. 

Aerosol carbon concentrations have been measured at two sites in the Los Angeles basin. Samples were analyzed for total carbon content and for elemental carbon content by the Gamma Ray Analysis of Light Elements technique and by several optical methods. Elemental carbon was shown to constitute a substantial fraction of total carbonaceous aerosol mass in the wintertime in Los Angeles. 

The relative contribution of primary and secondary carbon to urban aerosol is discussed in this paper. Some data from the ACKEX study in Los Angeles have been reexamined using new values for the carbon and lead emissions. Data on total carbon, elemental carbon and lead in fine particle samples collected in St. Louis are presented. Lead and elemental carbon have been shown to be useful tracers of primary carbonaceous aerosol. It is concluded that secondary carbon is most likely to be a significant portion of the urban carbonaceous aerosol in the summer and in the middle of the day. Secondary carbon can best be measured with short time resolution sampling (At 6h). 

Particulate carbon in the atmosphere exists predominantly in three forms elemental carbon (soot) with attached hydrocarbons organic compounds and carbonates. Carbonaceous urban fine particles are composed mainly of elemental and organic carbon. These particles can be emitted into the air directly in the particulate state or condense rapidly after Introduction into the atmosphere from an emission source (primary aerosol). Alternatively, they can be formed in the atmosphere by chemical reactions involving gaseous pollutant precursors (secondary aerosol). The rates of formation of secondary carbonaceous aerosol and the details of the formation mechanisms are not well understood. However, an even more fundamental controversy exists regarding... 

Rosen, Hansen, Dod and Novakov found a high correlation between optical absorptivity and the particulate carbon loading in 24-h samples from several California cities ( 5). Elemental carbon, a primary pollutant which is directly related to the absorptivity, was found to be a large fraction of the carbonaceous aerosol. They were able to place a low limit on the amount of secondary organic aerosol produced in correlation with ozone. 

In this paper we present results which reconcile the widely different results just discussed ranging from a carbon aerosol dominated by secondary organic material on the one hand to a carbon aerosol composed largely of primary carbon compounds on the other. We have employed an approach which uses lead or elemental carbon as a tracer for primary emissions and combines several analysis techniques to reexamine the published ACHEX data. We also present a new data set from St. Louis which is analyzed in a similar manner to contrast the aerosol in a midwestern city with that on the California coast. 

Fine Aerosol Mass Balance. The temporal variations of fine particle mass, total carbon, elemental carbon, nitrogen, sulfur and for a typical summer period (August 4-10, 1979) and... 

Finally, the use of aerosol lead and elemental carbon have been shown to be useful tracers for primary carbonaceous aerosol. If these data were combined with information on the detailed speciation of the organic carbon particles, a rather complete understanding of the carbonaceous aerosol would be possible. 

Finally, while elemental carbon is a common constituent of urban aerosols due to its combustion source, it is also found in particles in remote areas due to long-range transport (e.g., see O Dowd et al., 1993a and Saxena et al., 1995). 

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