Info

Coarse particle mass (fig m"3)

FIGURE 9.25 Correlation of bip with fine and coarse particulate mass (adapted from Groblicki et al., 1981).

cient 6sp to depend on the particular particle composition. Many studies have probed this relationship, coming at it from several different directions. One common approach has been to measure the chemical composition of particles and then test for empirical relationships between light scattering and chemical composition.

In this case, a best fit of the measured bsp to the chemical composition of the particles is often found using an equation of the form

where M, is the mass concentration of the ; th chemical species and a, is the light scattering coefficient for that species per unit concentration. Such a relationship has been applied in many studies and has proven useful in identifying certain species (e.g., sulfate, nitrate, and organics) as being important in terms of light scattering (e.g., see Groblicki et al., 1981; Appel et al., 1985; Vossier and Macias, 1986; Solomon and Moyers, 1986; McMurry et al., 1996; Eatough et al., 1996; Laulainen and Trexler, 1997; and Mctnnes et al., f 998). Values of a, are usually in the range between 1 and 20, with a typical value of ~5 m2 g '. Table 9.7 gives some values of a, reported for various common aerosol constituents.

However, as discussed in detail by Sloane (1986) and White (1986), Eq. (EE) only holds if all of the species act independently. There are several reasons to believe that in many cases they do not. For example, if one species is removed from a particle, not only will its contribution (a,M;) disappear but the particle size may

TABLE 9.7 Some Reported Values of the Light Scattering Coefficients ( at ) for Common Constituents of Atmospheric Particles"

Compound

(m2 g ')

Reference

Elemental (black) carbon

Was this article helpful?

0 0

Post a comment