Organic Tracers in Ambient Aerosols and Rain

Abstract

Partitioning of organic matter (i.e., solvent-extractable) was examined between ambient aerosols and rainwater particulate and dissolved phases. A rainfall event during April 10–11, 1982, was sampled in combination with 24-hour high-volume aerosol samples (before, during, and after the storm) at West Los Angeles and Pasadena, CA. Solvent-extractable organic matter (> C₁₅) was analyzed for total neutral and acidic components. These extract fractions were quantified by high-resolution gas chromatography and then screened for hydrocarbons, ketones, carboxylic acids as esters, alcohols, and polynuclear aromatic hydrocarbons (PAH) by high-resolution gas chromatography / mass spectrometry. Comparisons of the total mass loadings and chemical speciation were made between the total ambient aerosols and the filtered rainwater (with particles of diameters < 0.22 μm) and the rainwater particles isolated in situ (particle diameter > 0.22 μm). Both rain particles and ambient aerosols had significant levels of plant wax components, consisting of n-alkanes and n-alkanols ranging from C₂₁ to C₃₃ and from C₂₂ to C₃₀, respectively. The rain particles contained enhanced quantities of the oxygenated species that consisted of major amounts of n-alkanals (C₂₄–C₂₈) and free n-alkanoic acids (primarily C₁₆ and C₁₈). All samples had petroleum residues as indicated by the unresolved complex mixture (UCM) of hydrocarbons, n-alkanes with no carbon number predominance from C₁₆ to C₂₄ and minor molecular markers such as the 17α(H)-hopanes. In addition, PAH and diterpenoid residues from resins were present at low levels in both types of samples. Significant amounts of aromatic acids (e.g., benzoic, alkylbenzenedicarboxylic, phenyl-acetic, naphthoic, etc.) could be identified mainly in the rain particles but also in the ambient aerosols. Triphenyl phosphate and diphenylethylhexyl phosphate, both common plasticizers, were present in the aerosols as major resolved components, whereas various resolved phthalate plasticizers were common in all aerosol and rainwater samples. The sources of most of these marker compounds can be assigned and the partitioning of the major solvent extractable species could be evaluated with these data.