Info

West Los Angeles ^ Downtown Los Angeles □ Pasadena □

' aC31 ' ¡C32 ' aC32 ' ¡C33 ' aC33 ' ¡C34 ' aC34

FIGURE 9.47 Distribution of 2-methyl (i iso) and 3-methyl (a anteiso) alkanes measured in (a) cigarette smoke, (b) particles from abrasion of leaves typical of the Los Angeles area, and (c) annual average concentrations measured in three locations in southern California in 1982 (adapted from Rogge et al., 1994).

In addition, the i-C33 component is relatively more important in the leaf abrasion particles. Similarly, Kavouras et al. (1998) have shown that in addition to the concentrations and ratios of the iso- and anteiso-alkanes, there are other markers associated with the alkanes in cigarette smoke. For example, the CP1 for cigarette smoke was measured to be 3.44 compared to 1.41—1.66 for particles in urban and suburban areas. (The CP1 for rural areas was 4.53, reflecting the contribution from plant waxes.)

Figure 9.47c shows the annual average concentrations for these compounds in particles from three locations in southern California, from which the contribution of cigarette smoke to the ambient particulate matter is evident. The signature of cigarette smoke has also been observed in outdoor air particles in Crete, Greece (Kavouras et al., 1998). Indeed, based on such data, Rogge et al. (1994) estimate that cigarette smoke was responsible for about 1% of the outdoor fine particle concentrations in the Los Angeles area!

(2) Secondary organic aerosol formation Recall from the discussion of the kinetics, mechanisms, and products of the gas-phase oxidation of organics (Chapter 6) that a wide variety of multifunctional organics can be formed by reactions of even relatively simple organics commonly found in urban air. Some of these have sufficiently low vapor pressures that they will exist primarily in the condensed phase, i.e., in the form of particles. In particular, the oxidation of the larger and cyclic alkenes, aromatic hydrocarbons, and the larger alkanes and cycloalkanes is expected to lead to condensed-phase multifunctional organic products (e.g., see Grosjean and Seinfeld, 1989; Grosjean, f992) and this is indeed what is observed. For example, difunc-tionally substituted alkane derivatives of the type X-(CH2)„-X with n 1-5 have been observed in a number of studies in the Los Angeles area. The substituent X can be -COOH, -CHO, -CH2OH, -CH2ONO, -COONO, or -C00N02. Table 9.18 shows some of the difunctional species identified in submicron aerosols using high-resolution mass spectrometry (MS) of ambient particle samples introduced into the mass spectrometer by slow heating from 20 to 400°C; these compounds were present primarily in the submicron fraction of the particles, suggesting they were secondary in nature, that is, were formed from chemical reactions in the atmosphere (Schuetzle et al., 1975; Cronn et al., 1977). Similarly, the C3-C9 dicar-boxylic acids measured in southern California appear to be predominantly secondary (Rogge et al., f993d, 1996).

An idea of the complexity of the compounds found in air can be seen from the work of Yokouchi and

TABLE 9.18 Some Difunctionally Substituted Alkane Derivatives Found in Submicron Ambient Particles in Urban Air"

Compound

tl

hooc(ch2)„cooh

0 0

Post a comment