Co

4000 2000 1000 575 cm"1

Wavenumbers

FIGURE 9.49 Infrared spectrum of submicron (0.050-0.075 Aim) particles collected in Los Angeles (adapted from Mylonas et al., 1991).

remote region. Further rinsing with water removed most of the remaining peaks assigned to ammonium and sulfate.

Consistent with the earlier discussion of the contribution of crustal materials to larger particles, rinsing particles with diameters in the I- to 2-/tm range with water removed the peaks due to ammonium etc. but left peaks in the 1000- and 500-cm 1 regions, which are characteristic of minerals such as kaolinite and serpentine (Fig. 9.51).

Similar observations regarding the importance of polar organics in particles in rural and remote regions

Wavenumbers

FIGURE 9.50 FTIR spectra of particles from the Smoky Mountains, Tennessee, with diameters between 0.5 and 1.0 /¿m (top spectrum), after rinsing with acetone (middle spectrum) and then with water (bottom spectrum) (adapted from Blando et al., 1998).

Wavenumbers

FIGURE 9.50 FTIR spectra of particles from the Smoky Mountains, Tennessee, with diameters between 0.5 and 1.0 /¿m (top spectrum), after rinsing with acetone (middle spectrum) and then with water (bottom spectrum) (adapted from Blando et al., 1998).

4000 2000 1000 575 cm"1

Wavenumbers

FIGURE 9.49 Infrared spectrum of submicron (0.050-0.075 Aim) particles collected in Los Angeles (adapted from Mylonas et al., 1991).

have been reported by a number of researchers. For example, Mazurek et al. (1997) analyzed particles collected in the Grand Canyon area of the United States and found that the concentration of organics in fine particles was about equal to that of sulfate. Of the organics, about 25-50% could be analyzed by GC-FID, and of this, about half were highly polar compounds. Figure 9.52 shows the particle fine mass concentrations of the elutable organics at Hopi Point, divided into those that are acid (determined using derivatization to the methyl esters) and those that are neutral, as a function of elution time molecular size (Mazurek et al., 1997). Clearly, a large portion of the organics are acidic. For comparison, similar distributions are shown for the urban area in West Los Angeles, upwind at San Nicholas Island in the Pacific Ocean, and downwind at Rubidoux, near Riverside. The differences in distributions between the Grand Canyon sample and the urban samples suggest that long-range transport from this urban area was not important and that the organic portion of the particles at Grand Canyon may reflect naturally emitted biogenic hydrocarbons and their oxidation products (see Chapter 6 J).

Figure 9.52 also illustrates the effects of transport and oxidation in an urban area. Thus, the total amount of elutable organics and the acid fraction are both much smaller at the upwind San Nicholas Island site. However, as the air mass travels downwind over an urban area, both the concentration of particulate organics and the concentrations of acids increase (e.g., compare West Los Angeles to Rubidoux).

Although a clear anthropogenic signature was not evident in the particulate organics from the Grand Canyon area in Fig. 9.52, it has been reported in other studies of this region. For example, Cui et al. (1997) analyzed particles from Meadview, Arizona. They reported that lower molecular weight fatty acids ( C20) predominate over the larger acids expected from plant waxes (see Fig. 9.44) and for the C9 acids, there was no preference for the even C numbered species, indicating that they were likely due to anthropogenic sources. Phthalic acid was also observed and attributed to auto exhaust emissions.

In addition to inorganic nitrates, a variety of other forms of organic nitrogenous species also exist in particles. For example, Novakov and co-workers, using X-ray photoelectron spectroscopy (XPS), observed reduced nitrogen species tentatively identified as amines, amides, and possibly nitriles (Novakov et al., 1972; Gundel et al., 1979; Chang et al., 1982). Similarly, Gundel and co-workers (1993) report the presence of nitro compounds, organic nitrates or nitrites, amines, and amides in the polar fraction of organics in particles collected in Elizabeth, New Jersey, and Kneip et al. (1983) report A^-nitroso compounds in particles collected in New York City. These compounds, which they call Nx species, often comprise a major portion of the particulate nitrogen; for example, in particles collected in Berkeley, California, in November 1976, of the total nitrogen present, 50% was identified as the reduced Nx species. Much of this appears to be in the form of organic amides, which can be hydrolyzed to the acid co

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