Carbonaceous aerosols in the

Huntzicker, J.J. Johnson, R.L. Shah, J.J. "Carbonaceous aerosol in the vicinity of a Lurgi gasifier", presented at the Second Chemical Congress of the North American Continent, Las Vegas, Nevada, August 1980. 

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). 

Kadowaki, S., Characterization of Carbonaceous Aerosols in the Nagoya Urban Area. 2. Behavior and Origin of Particulate n-Alkanes, Environ. Sci. Technol., 28, 129-135 (1994). 

Ke L, Zheng M, Tanner RL, Schauer JJ (2007) Source contributions to carbonaceous aerosols in the Tennessee valley. Atmos Environ 41 8898-8923... 

Cachier H (1995) Combustion carbonaceous aerosols in the atmosphere implications for ice core studies. Ice Core Studies of Global Biogeochemical Cycles, NATO ASI Series, Springer, Berlin, pp 313-346... 

Sciare J, Oikonomou K, Favez O, Markaki Z, Liakakou E, Cachier H, Mihalopoulos N (2008) Long-term measurements of carbonaceous aerosols in the Eastern Mediterranean evidence of long-range transport of biomass burning. Atmos Chem Phys 8 5551-5563... 

Carbonaceous aerosols in the atmosphere are complex in nature and are found in both coarse particles (> about 2.5 pm) and fine particles (< about 2.5 pm). Sources of carbon-containing particles are varied and include resuspended soil particles, pollen, plant waxes, etc. in the coarse fraction, and soot particles, sorbed organics including PAHs, and secondary aerosols resulting from... 

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. 

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... 

The ratio of elemental (EC) to organic carbon (OC) has been measured in many studies and is commonly found to be less than one. For example, Shah et al. (1986) measured EC and OC in particles from both urban and rural areas across the United States and found the urban average concentrations to be 6.6 /xg m 3 for OC and 3.8 gg m 3 for EC, i.e., a ratio of EC OC of 0.6. Similarly, in the Los Angeles area, EC typically represents about a third of the carbonaceous component of particles (Rogge et al., 1993d). For rural areas, the concentrations were about a third of those in the urban areas, but the ratio was about the same, at 0.5, consistent with ratios of 0.4-0.5 measured in the Ohio River Valley by Huntzicker et al. (1986). Novakov et al. (1997) measured carbonaceous aerosol off the east coast of the United States at altitudes from 0.2 to 3.0 km and report that the ratio of EC OC is 0.1. 

Whitby K.T., Size distribution and physical properties of combustion aerosols. Proc. Conf. on Carbonaceous Particles in the Atmosphere, Lawrence Lab., Berkeley, California Publication of LBL 1979, LBL-9037, 35 pp. 

Shah J. J., Measurements of carbonaceous aerosol across the US Sources and role in visibility degradation, Ph. D. thesis, Oregon Graduate Center, Beaverton, Oregon (1981). 

Some work [5] has been performed on the photochemical reaction between sulfur dioxide and hydrocarbons, both paraffins and olefins. In all cases, mists were found, and these mists settled out in the reaction vessels as oils with the characteristics of sulfuric acids. Because of the small amounts of materials formed, great problems arise in elucidating particular steps. When NO and 02 are added to this system, the situation is most complex. Bulfalini [3] sums up the status in this way The aerosol formed from mixtures of the lower hydrocarbons with NO and S02 is predominantly sulfuric acid, whereas the higher olefin hydrocarbons appear to produce carbonaceous aerosols also, possibly organic acids, sulfonic or sulfuric acids, nitrate-esters, etc. ... 

When sources are studied, several things should be done to provide data needed for receptor-model applications. First, particles should be collected In at least two different size fractions corresponding to the division at about 2.5-ym dlam now used In many studies of ambient aerosols. In some cases. It may be desirable to have more size cuts. As noted above, compositions of particles from coal combustion change dramatically below about 0.5-pm dlam (44, 46). Above we Identified a minimum of about twenty elements that should be measured. Also, In order to develop adequate markers for sources that emit carbonaceous particles, measurements of organic compounds and other properties related to carbonaceous particles should be made. 

Table 3 summarizes the 1979 annual average particle extinction coefficient and the mass concentrations of the fine aerosol chemical species estimated by statistical analysis of the 61 filter samples. Organics and sulfates dominated the chemically determined fine aerosol mass at China Lake in 1979. A linear least squares fit between molar concentrations of NHt and SO gave a zero intercept, a slope of 1.87 and a correlation coefficient of 0.98. It is therefore assumed that the fine sulfate aerosol was in the form of ammonium sulfate. The mass concentration of carbonaceous and sulfate aerosols were, on the average, comparable in magnitude. 

The quality of statistically inferred species extinction balances can be enhanced with proper aerosol sampling. Due to its important role in light scattering, only the fine aerosol should be sampled. A mass balance should account for all major fine particle species. Ideally the particle scattering coefficient should be measured directly at the location where aerosol is sampled by the filters. The importance of soot and other carbonaceous aerosol contributions to light extinction in arid regions should not be overlooked. 

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. 

Ambient aerosols, particularly those with diameters less than 3pm, are a serious pollution problem. Carbonaceous material is a major component of the fine particle concentration (10 and has undergone extensive study in the past few years (, ) in large part because of the concern that these particles play an Important role in urban haze and community health. 

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 have shown that there is no simple answer to the question posed in the title of this paper. Primary carbon particles dominate the carbonaceous aerosol under certain conditions while substantial secondary carbon may be present at other times. However, the importance of secondary carbon contributions is much less obvious when 24-h samples are examined. With shorter time averaged samples (e.g. 6-h or less) the increase in secondary carbon formation can be more easily detected. Secondary carbon appears to be more important in the summer rather than winter, in the afternoon father than the early morning, and in LA rather than St. Louis. It should be noted that these conditions of increased secondary carbon aerosol formation are also more favorable conditions for photochemical reactions. Our detailed emission inventory Indicates that much more primary carbon exists in the urban aerosol than was thought previously. This is in agreement with the data. Our analysis shows that even on the very smoggy days in the ACHEX study there were times when primary carbon dominated the carbonaceous aerosol. 

The symposium was divided into four subject areas, and this volume follows that general format. The first group of chapters reviews and describes many of the recent modeling efforts. The next section is devoted to source characterization studies, while the third group includes chapters concerned with carbonaceous aerosols—both source apportionment and measurement techniques. The final section describes the results of several field studies in areas of the United States and China where wind-blown dust is a serious problem. 

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