Chemical Signatures of the Los Angeles Aerosol (d_p < 3.5 μm)

Abstract

The frequency distributions of the chemical components of the Los Angeles aerosol measured over a 1-year period are approximately lognormal. For nonreactive aerosol components, the geometric standard deviation (GSD) is nearly constant at 1.85 ± 0.14, even for components from different source types. The GSD of CO is lower than those of the nonreactive aerosol species, which, in turn, tend to be lower than those of the reactive aerosol species. A possible explanation is offered based on the equation for mean square fluctuating compositions in a turbulent fluid. An apparent bimodal frequency distribution for sulfates probably corresponds to the two differing reaction pathways by which gas-to-particle conversion occurs. The composition of the aerosol corresponding to the most probable total aerosol mass concentration is reported. This composition differs from the simple average chemical composition, and may be more appropriate for certain applications.