The combined distribution, represented by the me, masks the contributions

of the individual modes, shown by dashed lines and does not show the nature of

The more or less straight-line portion of the distribution between 0.1 and 10 μm

can be represented by an inverse power law distribution (the Junge distribution)

the surface or mass distributions.

For the data shown in Figure 14.2a,

AN

A log(d,)

= 24.0d-3.08

for d in um. Equation 14.1 is empirical; there is no fundamental or theoretical rea-

son that the atmospheric aerosol should have this distribution function.

Mode

Nuclei

Accumulation

Coarse Particle

Data from Whitby (1978).

Figure 14.2b presents the urban aerosol size distribution as cumulative number

and volume distributions on a log-probability graph. (See Section 4.5.) The distri

butions show significant departures from a lognormal distribution, and the contri-

butions of the individual modes are hidden. Figures 14.2c and 14.2d respectively

show particle number and volume per unit log interval on an arithmetic scale ver-

TABLE 14.3 Modal parameters for average urban aerosol.ª

CMD

CN

(µm)

(cm-³)

0.014

0.054

0.86

GSD

1.80

2.16

2.21

106,000

32,000

5.4

(14.1)

Cvol

(µm³/cm³)

0.63

38.4

30.8 sites for the cataly

thropogenic chlorofluorocarbons (r

to atomic chlorine (CI), which reacts with ozone (O3) to form oxygen (O₂) and chlo

rous acid (HOCI). In the polar spring, the sun photodissociates these compounds

keeps repeating with the continued destruction of ozone. Volcanic eruptions enhance

this process by increasing the stratospheric aerosol, which migrates to the poles and

provides additional surface for the catalytic activation of chlorine. See Seinfeld and

Pandis (1998).

PROBLEMS

14.1 For the modal data given in Table 14.3, what is the particle number per unit

mass for each mode? Assume standard particle density.

Nyeki,

distrib

5211-

Puesche

383-

Schwar

Ant

SMIC,

MI

Sienfe

Whit

(1

Fig: 1