The characterization of carbonaceous particulate matter is of interest since it constitutes significant percentages of aerosol mass; it may alter the hygroscopicity of aerosols; and it contributes to both light scattering and absorption, with consequent visibility and climate effects. Although natural sources of organic aerosol are significant, anthropogenic activities have clearly affected the cycling of organic species. Much of the research has focused upon urban areas, where organic emissions are large and have dramatic effects upon air quality and particulate mass concentrations. Rogge et al. [1993] discuss the use of high-resolution gas chromatography (HRGC) and gas chromatography/mass spectrometry (GC/MS) to quantify single compounds in organic aerosol samples taken over an annual cycle at urban sites in southern California. Molecular marker techniques can be used to identify contributions of sources such as wood smoke and biogenic emissions ( Mazurek et al. [1991]).
The degree of secondary organic aerosol formation in the Los Angeles basic was assessed from comparisons of measurements with transport model predictions ( Hildemann et al. [1993]). That study determined that the fraction of elutable organic aerosol that may be secondary in origin was between about 18 and 27%. The study of Turpin and Huntzicker [1991] attributed a much higher fraction to secondary formation during air pollution episodes. Assessment of natural vs. anthropogenic and of primary and secondary organic contributions to aerosol in urban and non-urban regions is likely to be an important research area in the future.