Total carbon particle emissions

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). 

Few comprehensive classification schemes for CCP exist. The American Society for Testing and Materials (ASTM 1994) classifies two catgories of fly ash (Class F and Class C) based upon chemical and physical properties of the fly ash (the total amount of Si + A1 + Fe, sulphate, loss on ignition). This classification system was developed for the use of fly ash as an admixture in concrete. More recently, new classification schemes have been developed that place emphasis on textural descriptions, the form of carbon (or char ), and the surface properties of fly ash (Hower Mastalerz 2001). These new classification schemes for fly ash may be the result of growing concern over mercury emissions from coal-fired boilers. Studies have shown that mercury adsorption onto the surface of fly ash particles is a function of both the total carbon content and the gas temperature at the point of fly ash collection (Hower et al. 2000). 

Composition and size distribution of the emitted particles depend on the contribution of the individual emission sources related with road traffic—in particular combustion and non-tail-pipe emissions. Tailpipe emissions are vehicle exhaust emissions which are produced during fuel combustion (including additives) and released through the vehicle tailpipe (Rogge et al. 1993 Cadle et al. 1999). The particles derived from tail-pipe emissions are mainly composed of EC and OC, thus average total carbon emission rates are usually very close to the PM mass emission rates. Inorganic anions account for some percent of total tail-pipe emissions, the contribution of the elemental fraction is also in the order of few percent. 

A characteristic of old diesel engines was black soot in their exhausts caused by the combustion process itself in which very small atomized droplets of fuel burning in hot compressed air left an unbumt core of fine carbon particles onto which other species in the exhaust gas adsorbed [26-28]. The total particulate matter emissions of diesel exhaust are comprised of three main components. One component is the solid carbonaceous fraction, which is the visible soot emissions commonly associated with diesel exhaust A second component is the soluble organic fraction (SOF). The SOF can exist either as a vapor or as an aerosol depending of the temperature of the diesel exhaust These liquids arise from imbumed or partially burned diesel fuel or lubricating oil swept from the cylinder walls of the engine [29]. 

Radiation differs from conduction and convection not only in mathematical structure but in its much higher sensitivity to temperature. It is of dominating importance in furnaces because of their temperature, and in ciyogenic insulation because of the vacuum existing between particles. The temperature at which it accounts for roughly half of the total heat loss from a surface in air depends on such factors as surface emissivity and the convection coefficient. For pipes in free convection, this is room temperature for fine wires of low emissivity it is above red heat. Gases at combustion-chamber temperatures lose more than 90 percent of their energy by radiation from the carbon dioxide, water vapor, and particulate matter. 

In densely populated areas, traffic is responsible for massive exhausts of nitrous oxides, soot, polyaromatic hydrocarbons, and carbon monoxide. Traffic emissions also markedly contribute to the formation of ozone in the lower parts of the atmosphere. In large cities, fine particle exposure causes excess mortality which varies between one and five percent in the general population. Contamination of the ground water reservoirs with organic solvents has caused concern in many countries due to the persistent nature of the pollution. A total exposure assessment that takes into consideration all exposures via all routes is a relatively new concept, the significance of which is rapidly increasing. 

Combined Gas, Soot, and Particulate Emission In a mixture of emitting species, the emission of each constituent is attenuated on its way to the system boundary by absorption by all other constituents. The transmissivity of a mixture is the product of the transmissivities of its component parts. This statement is a corollary of Beer s law. For present purposes, the transmissivity of species k is defined as xk = 1 — Et. For a mixture of combustion products consisting of carbon dioxide, water vapor, soot, and oil coke or char particles, the total emissivity eT at any wavelength can therefore be obtained from... 

Estimates of annual amounts of emissions released into the earth s atmosphere are remarkably different from each other, depending on the choice of balance models [5-24]. For the anthropogenic sources, the following substances may be listed in decreasing order of importance carbon dioxide, carbon monoxide, sulphur oxides, hydrocarbons, nitrogen oxides and liquid and solid particles. A summary of relative contributions of these substances to total emissions of main types of anthropogenic sources is given in Table 5.8. 

Real-world emission rates of in-use motor vehicles (road traffic) can be quantified by measurements in road mnnels. The results reported for particle mass emissions in PMio varied from several mg veh km to some hundred mg veh km , with reduced amounts for the fine particle fraction PM2.5. The particles released mainly consist of EC, OC, soluble ions (NHj, S04 , NOs ) and mineral components (Si, Fe, Ca, Al, Mg). Trace metal emissions (Ba, Co, Cr, Cu, Mn, Ni, Pb, Sb, Sn, Sr, Ti, V, Zn) contribute usually for less than 1 % of total emissions in all size fractions. Observed particulate vehicle emissions could be attributed to several tailpipe and non-tailpipe sources. The main part of carbon emissions may be contributed to tail-pipe exhaust fraction, whereas the non-carbon emissions are most likely non-exhaust derived components. PMjo emissions are usually dominated by resuspended matter as well as by brake wear, whereas fine particles (PM2.5) are mainly derived from combustion processes. 

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