Elemental Carbon Fractions Research Articles

Size segregated light absorption coefficient of the atmospheric aerosol

The light absorption coefficient of atmospheric aerosols in the visible can be determined by depositing the particles on a filter and measuring its “transmission” in a special optical arrangement. With an impactor with rotating impaction plates producing a homogeneous deposit, it is possible to extend this technique to size segregated aerosol samples. A simultaneous determination of the mass size distribution is possible. Test measurements with black carbon aerosol have shown the feasibility of this method. Samples of the atmospheric aerosol have been taken in and near Vienna, in Naples and near Bologna. The light absorption of the aerosol is always highest for particle diameters between 0.1 and 0.2 μm. Only in the humid environment of the Po valley it had a slightly larger peak size, whereas the size of the nonabsorbing particles increased considerably. The light absorption of the atmospheric aerosol is always higher in an urban environment. 'The mass absorption coefficient of the aerosol at all four locations was very similar, and completely different from values which could be. expected using effective refractive indices which are frequently used in models. Using the data measured in this work two alternate models for the effective refractive index and black carbon content of the aerosol are suggested: (a) a size-dependent refractive index, where the imaginary part varies from −0.25 for particles smaller than 30 nm to − 0.003 for particles larger than 2 μm; this could especially be applied if an internal mixing of the aerosol is to be expected, or (2) a size-dependent fraction of elemental carbon in the case of external mixing with 43% of carbon particles for sizes below 30 nm decreasing to 10% for sizes up to 0.4 μm.

The influence of aerosol particle composition on cloud droplet formation

A difference in partitioning between cloud droplets and interstitial air for two chemical species (elemental carbon and sulphur) with different expected behaviour in nucleation scavenging was observed in clouds at Mt. Kleiner Feldberg (825 m asl), near Frankfurt, Germany. The fraction of sulphur incorporated in cloud droplets was always higher than the fraction of elemental carbon. This difference in partitioning has also been observed in fog but under different pollution conditions in the Po Valley, Italy. Both these studies were based on bulk samples. In the present study at Kleiner Feldberg, impactor samples of the particles in the interstitial air and the cloud droplet residuals were taken and a single particle analysis was done on the samples. It was found that, for a given particle size, the majority of particles forming cloud droplets were soluble and that insoluble particles preferentially remained in the interstitial air.

Volatility of elemental carbon

A volatility technique whereby aerosol particles are heated to the relatively high temperature of 860 °C is used to infer the presence of elemental carbon in polluted air masses in the vicinity of the west coast of Ireland. The volume of elemental carbon for submicrometre sized particles contained in the aerosol is estimated from the fall off in number concentration at a critical onset temperature of about 730–735 °C, as also obtained for laboratory carbon ink aerosol. The technique permits determination of the elemental carbon volume percentage of the total fine aerosol volume, and an estimation of the abundance of elemental carbon contained within the black carbon fraction of the atmospheric aerosol. Supplementary black carbon mass concentration measurements were obtained using a thermal method and an aethalometer absorption method. The work suggests that elemental carbon can be identified using the volatility technique and that it can yield size‐segregated information on the fraction of elemental carbon in atmospheric aerosol.

Characteristics of airborne particles inside southern California museums

The concentrations and chemical composition of suspended particulate matter were measured in both the fine and total size modes inside and outside five southern California museums over summer and winter periods. The seasonally averaged indoor/outdoor ratios for particulate matter mass concentrations ranged from 0.16 to 0.96 for fine particles and from 0.06 to 0.53 for coarse particles, with the lower values observed for buildings with sophisticated ventilation systems which include filters for particulate matter removal. Museums with deliberate particle filtration systems showed indoor fine particle concentrations generally averaging less than 10 μg m −3. One museum with no environmental control system showed indoor fine particle concentrations averaging nearly 60 μg m −3 in winter and coarse particle concentrations in the 30–40 μg m −3 range. Analyses of indoor vs outdoor concentrations of major chemical species indicated that indoor sources of organic matter may exist at all sites, but that none of the other measured species appear to have major indoor sources at the museums studied. Significant fractions of the dark-colored fine elemental (black) carbon and soil dust particles present in outdoor air are able to penetrate to the indoor atmosphere of the museums studied, and may constitute a soiling hazard to works of art displayed in museums.

Phase partitioning for different aerosol species in fog

Simultaneous measurements of several non-volatile species in unscavenged aerosol particles and in fog droplets have revealed differences in partitioning for different chemical species. The average scavenged fraction of sulphate was 18% and the corresponding fraction of elemental carbon was only 6%. This suggests that the aerosol was externally mixed, and that the chemical mixture of the aerosol as a function of size is important in the context of nucleation scavenging. The measurements obtained could not distinguish between the two primary hypotheses for explaining the observed differences, (a) that the particles had the same size distribution and their chemical composition was the controlling factor, and (b) that the elemental carbon was associated with smaller particles than the sulphate, so that the difference in scavenging efficiency was controlled by the size distribution of the particles. DOI: 10.1034/j.1600-0889.1992.t01-2-00008.x

Chemical source profiles for particulate motor vehicle exhaust under cold and high altitude operating conditions

The chemical compositions of fine particles in motor vehicle exhaust were measured on dynamometer and in situ exhaust samples during the winter in Denver, CO (elevation ∼ 1600 m above sea level). Forty-one inorganic and other species were quantified for tests involving different vehicle types, different fuels, and different operating cycles. It was found that addition of ethanol or MTBE (methyl tertiary butyl ether) to leaded and unleaded gasoline (in order to lower CO emissions) has no major effect on the chemical composition of particulate emissions from motor vehicles. On the Federal Test Procedure (FTP) driving schedule but at temperatures of 0 to 5 °C to simulate Denver winter conditions, compositions of emissions were similar among the cold-transient, cold-stabilized, and hot-transient cycles in the case of the leaded-fuel vehicles and also in the case of the diesel vehicles. Cold starts do cause a major change in the composition of emissions from unleaded catalyst-equipped vehicles by increasing the elemental carbon. Two-stroke diesel buses emit a much higher fraction of organic carbon and a much lower fraction of elemental carbon than do cars or four-stroke diesel trucks.

Source apportionment of carbonaceous aerosol in New York City by multiple linear regression.

A multiple linear regression model was applied to aerosol chemical data from New York City to determine the sources of carbonaceous aerosol. The model used elemental tracers for auto exhaust aerosol (Pb), residual oil combustion (V), resuspended dust (Mn or Fe), and incineration (Cu or Zn). Although relative uncertainties in the source apportionment were greater than 20%, auto exhaust was found to be the main source of organic carbon with lesser contributions from other sources. A substantial fraction of elemental carbon could not be associated with the sources used in the model and was possibly associated with the combustion of diesel and distillate oils. The regression coefficients, which are related to source composition, compared well with actual measured source compositions. Because of the uncertainties it was concluded that source apportionment, especially as it relates to the development of control strategies, should utilize the results of several receptor and source models where possible. 12 references.

Characteristics and consequences of soot in the atmosphere

Soot, as defined in this paper, consists of the primary carbonaceous particulate emissions from combustion sources. In the simplest terms, it can be divided into an organic carbon fraction that consists of a large number of organic compounds, and an elemental carbon fraction that has a graphite-like structure with many structural defects. It is because of these defects that elemental carbon absorbs light, reduces visibility, and serves as a catalyst for certain chemical reactions in the atmosphere. Presently, two of the most important sources of soot are diesel engines and woodburning, but virtually every process that burns carbonaceous fuel emits soot. As a result of the ubiquitous emission sources, measurable concentrations of soot occur in remote as well as urban areas. As expected, urban and suburban areas experience the highest concentrations. However, significant amounts of soot are found in remote areas such as the Arctic because of the long residence time of the soot particles in the atmosphere. In addition, the soot appears to be present in some areas in sufficient amounts to be a significant contributor to visibility reduction.

Highway motor vehicles as sources of atmospheric particles: Projected Trends 1977 to 2000

Highway motor vehicle emissions contribute to the total atmospheric particulate matter burden. The possible health and welfare effects of these emissions depend upon their composition and concentration in the atmosphere, the exposure of man and materials, and in some instances the length of time of the exposure. The characteristics of long-term national and mesoscale (citywide) exposures and short-term localized (congested freeway, city street canyon) exposures to mobile source particles were examined for 1977 and 1988, and estimated for 2000. Because of interest in the possible impact of passenger car dieselization on atmospheric particle concentrations, three degrees of diesel penetration (5%, 10% and 20% of light-duty sales by 2000) were examined with and without an assumed scenario of particulate matter emissions regulation. Generally, urban concentrations of mobile source particles ranged from about 2 to 10 μg/m 3 in 1977; lower concentrations occurred in suburban areas and higher concentrations occurred in city central core areas. However, concentrations of nearly 80 μg/m 3 could be experienced on congested freeways with low velocity, near parallel winds. Due primarily to decreases in the number of vehicles using leaded gasoline, the mobile source particulate matter burden is projected to be less in 1988 and 2000 than in 1977; the degree to which the burden will lessen depends upon the level of dieselization and the degree of regulation. The compositional characteristics of the particles will also change. The outyear fractions of lead will decrease and the fraction of elemental and organic matter carbon will increase. Heavyduty diesel motor vehicles will become the single most important source of mobile source particles. Knowledge of vehicle usage patterns will then become important for classical dispersion model estimation of emissions impact, since truck kilometer traveled will likely not be uniformly distributed across cities.

Possible production by lightning of aerosols and trace gases in Titan's atmosphere

Although lightning has not yet been observed in Titan's atmosphere, the presence of condensable vapors and the deposition of a significant amount of solar energy at the surface suggest the possibility of lightning activity. Based on an understanding of the relationship of lightning activity to the amount of convective energy available on Titan, a lightning energy dissipation rate of 4 × 10 −6, W/m 2 can be expected. This value is much lower than that for Earth or Jupiter, and is a result of both the reduced solar flux at Titan and the absorption of sunlight by the aerosols that lie above the convective layer. For this dissipation rate, the amount of HCN and C 2N 2 produced by lightning should be greater than that by solar UV, but could be less than that produced by electron precipitation and galactic cosmic rays. Equilibrium calculations indicate that large mole fractions of elemental solid phase carbon will also be produced. Using a simplified model of aerosol formation, coagulation, and settling, it is estimated that a lightning-produced aerosol could have a typical optical depth of 10 −2, with values as high as 0.1. The accumulation of soot over geological time might reach a meter or more in depth.

Determination of organic and elemental carbon in atmospheric aerosol samples by thermal evolution

A simple apparatus is described for determination of volatile organic and elemental carbon fractions in filter-collected atmospheric aerosol samples. The two-step technique involves rapid heating and thermoevolution of organic carbon at 400/sup 0/C in helium carrier gas, followed by removal of elemental carbon at 700/sup 0/C in 10% O/sub 2//He. Evolved carbon is converted to CO/sub 2/ on copper oxide catalyst, purified, and analyzed by nondispersive infrared (NDIR) spectrometry. Flash heating of ambient aerosol samples minimizes organic-to-elemental carbon conversion, allowing determination of organic and elemental carbon fractions with relative standard deviations of +/-8% and +/-12%, respectively, for total carbon loadings of 6-50 ..mu..g of C/cm/sup 2/ filter area. Blank filter variability, sample heating duration, and the effects of sample heating rates and pyrolysis temperature are evaluated. Ambient aerosol carbon data from both urban and remote sampling sites are presented and discussed.

The 13C/ 12C ratio in black pulmonary pigment: A mass spectrometric study

Ratios of the two stable isotopes of carbon, 13C and 12C, were measured in black pulmonary pigment and in several endogenous tissues removed during 20 autopsies on Long Island, New York. The mass spectrometer used for carbon isotope ratio analyses has a precision of ±1 13C atom per million carbon atoms. The 13C/ 12C ratio was found to be distinctly lower in black pulmonary pigment than in endogenous tissues, the mean difference amounting to 65 13C atoms per million carbon atoms. The results demonstrate that the elemental carbon fraction of black pulmonary pigment is exogenous and constitutes roughly 30 per cent of the weight of the pigmented material. It was also observed that 13C/ 12C ratios in endogenous tissues from individual autopsy cases were not quite identical, tending to be slightly greater in corpus callosum than in liver or peripheral lung.