Aerosol source strengths

Lewis, C. W., and R. B. Zweidinger, Apportionment of Residential Indoor Aerosol VOC and Aldehyde Species to Indoor and Outdoor Sources, and Their Source Strengths, Atmos. Environ., 26A, 2179-2184 (1992). 

In this study we have employed the simultaneous collection of atmospheric particles and gases followed by multielement analysis as an approach for the determination of source-receptor relationships. A number of particulate tracer elements have previously been linked to sources (e.g., V to identify oil-fired power plant emissions, Na for marine aerosols, and Pb for motor vehicle contribution). Receptor methods commonly used to assess the interregional impact of such emissions include chemical mass balances (CMBs) and factor analysis (FA), the latter often including wind trajectories. With CMBs, source-strengths are determined (1) from the relative concentrations of marker elements measured at emission sources. When enough sample analyses are available, correlation calculations from FA and knowledge of source-emission compositions may identify groups of species from a common source type and identify potential marker elements. The source composition patterns are not necessary as the elemental concentrations in each sample are normalized to the mean value of the element. Recently a hybrid receptor model was proposed by Lewis and Stevens (2) in which the dispersion, deposition, and conversion characteristics of sulfur species in power-plant emissions... 

In these discussions we will thus use the following explicit definition of a chemical measurement in the atmosphere the collection of a definable atmospheric phase as well as the determination of a specific chemical moiety with definable precision and accuracy. This definition is required since most atmospheric pollutants are not inert gaseous and aerosol species with atmospheric concentrations determined by source strength and physical dispersion processes alone. Instead they may undergo gas-phase, liquid-phase, or surface-mediated conversions (some reversible) and, in certain cases, mass transfer between phases may be kinetically limited. Analytical methods for chemical species in the atmosphere must transcend these complications from chemical transformations and microphysical processes in order to be useful adjuncts to atmospheric chemistry studies. 

This aerosol traveled a maximum sampled distance of some 450 miles and covered an area of over 34,000 square miles. The concentration of particles in this aerosol could have been increased by increasing the source strength, which was small in this case. 

The strength of various natural and anthropogenic aerosol sources is tabulated in Table 17 (SMIC, 1971). The precision of estimates is represented by the intervals given. For further details, the interested reader is referred to the original work. 

On the basis of atmospheric measurements, Chin and Davis (1995) estimated the total quantity of OCS in the atmosphere to be 5.2 Tg, of which 4.63 Tg is in the troposphere and 0.57 Tg in the stratosphere. Based on the estimated global OCS source strength of 0.86 Tg yr 1, the global atmospheric lifetime of OCS is estimated to be about 6 years. We will return to the global cycle and chemistry of OCS in Chapter 5 in connection with the stratospheric aerosol layer. 

TABLE 22.7 Source Strength, Atmospheric Burden, Extinction Efficiency, and Optical Depth for Various l pes of Aerosols... 

The column burden of sulfate aerosol, m Q2, can be estimated from the global source strength of SO2, 0sO i the average fractional conversion of SO2 to sulfate in the atmosphere, vso, the mean residence time of sulfate aerosol in the atmosphere, t q , and the area, A, of the geographical region over which the estimate is performed (e.g. the entire globe, the Northern Hemisphere, etc.), as... 

Chemical mass balances have been used to calculate the source contributions to rainwater chemistry(3,4,17). The source strength model as described by Miller et al.(28) was developed to determine the contribution of different aerosol sources to the ambient particulate aerosol from the chemical composition of the source emissions and the ambient aerosol. The percentage of the ith element in the ambient sample, p, was given by... 

As we have seen, a great deal is known about emission sources and strengths, ambient levels, and mutagenic/carcinogenic properties of the particle-phase PAHs in airborne POM. However, because of the tremendous physical and chemical complexity of the aerosol surfaces on which photolysis, photooxidations, and gas-particle interactions take place in real polluted ambient air, much less is known about the structures, yields, and absolute rates and mechanisms of formation of PAH and PAC reaction products, especially for the more polar PACs. This is one area in which there exists a major gap in our knowledge of their atmospheric chemistry and toxicology. 

Besides the major aerosol formation mechanisms discussed in the previous section other processes also produce atmospheric particles. The strength of these sources can be neglected on global scale. However, the effect of particles formed in... 

The source density (p can depend on the concentration a at the point (x, t), provided that tp is statistically independent of the wind field (see Appendix B). Such a dependence, so that ip = ip(Xy t, a), is indicated in Eq. (16). In this case Eq. (16) becomes an integral equation in a which must be solved by recursive or other means, rather than an explicit solution for a. This issue does not arise when the source density is specified independently, for instance, by the locations and strengths of point sources of air pollutants. However, it is crucial in most biogeochemical applications, becau.se the. source or sink densities for entities such as heat, water vapor, CO2, and aerosols depend on the ambient concentrations of those entities. The inclusion of this dependence in Eq. (16) is considered in Appendix B, and the practical implications are further discussed in Section 3.5. 

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