" From Hahn (1980) and Ketseridis et al. (1976). h See Chapter 10.

States during dust storms, as much as 1000 /ig m 3, with arsenic levels as high as 0.4 /¿g m 3 (Reid et al., 1994).

Similarly, the plume from the burning of oil wells in Kuwait had an unusual composition, containing both soot and significant salt concentrations due to brine mixed in with the oil see, for example, the special section in the Journal of Geophysical Research, Vol. 97 (D13), September 20, 1992 .

Plumes from biomass burning can also have unique signatures. For example, organics, ammonium, potassium, sodium, nitrate, nitrite, sulfate, chloride, phosphate, elemental carbon, and the anions of organic acids (formate, acetate, oxalate, etc.) have all been measured in particles in the plumes from burning vegetation (e.g., see Cofer et al., 1988; Andreae et al., 1988; and Artaxo et al., 1994).

In short, while there are many common elements and size distributions in tropospheric particles found in many areas around the world, it is important to recognize that in some circumstances, the particle composition and size distributions may be unique.

2. Organics

While inorganics, particularly sulfates and nitrates, tend to be ubiquitous components of tropospheric particles, in many cases a large portion of the mass lies in organic compounds. The composition of the organics is complex, even in remote areas with negligible contributions from combustion processes. We first discuss typical organics found in remote areas, and then those characteristic of polluted urban areas. For a discussion of the history of this field and a collection of papers on this topic, see the Proceedings of the Fifth International Conference on Carbonaceous Particles in the Atmosphere J. Geophys. Res., 101, 19373-19627 (1996).

a. Biogenically Derived Organics in Aerosol Particles

Table 9.17 shows some of the organics identified in nonurban aerosols. A wide variety of organics are found, including alkanes, alkenes, aromatics, fatty acids, alcohols, and organic bases.

n-Alkanes in the C,5-C35 range are common components of nonurban aerosols. As seen in Fig. 9.43, there is a preference for compounds with odd numbers of carbon atoms. This is expressed in terms of the carbon preference index (CPI) (Cooper and Bray, 1963), which for alkanes is the sum of the odd carbon number alkanes over the sum of the even carbon number alkanes. It is often applied to restricted carbon number ranges to separate out different sources.

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