Interpretation of High-Resolution Gas Chromatography and High-Resolution Gas Chromatography / Mass Spectrometry Data Acquired from Atmospheric Organic Aerosol Samples

Abstract

Major chemical features of the solvent-soluble organic aerosol carbon fraction (i.e., carbon range C_8–C_(36)) are quantified and identified by high-resolution gas chromatography (HRGC) and high-resolution gas chromatography / mass spectrometry (HRGC / MS). Through these methods, bulk characteristics of the atmospheric aerosol are denned and reveal information relating to seasonal variations and specific source contributions to the atmospheric organics complex mixture. Fine aerosol samples from West Los Angeles, CA show lowest monthly average ambient concentrations of the total extractable organic carbon fraction during summer (e.g., 2.03 μg/m^3) and highest levels during winter (e.g., 5.18 μg/m^3), when sampled at 6-day intervals over the 1982 annual cycle. Absolute concentrations of the complex solvent-soluble organic acid fraction also indicate a similar pattern where a summer minimum and winter maximum are observed. Molecular marker characterizations are performed for the suite of n-alkanes (C_(20)–C_(36)) and for n-alkanoic acids (C_8–C_(30)). Carbon preference index (CPI) values and carbon number maxima (C_(MAX)) are generated for both homologue series. Petroleum residues constitute the major contribution to the organic aerosol, as indicated throughout the entire annual cycle by the low CPI values (1.02–1.83) and by the predominant C_(MAX) (C_(25)) of the n-alkanes. A minor presence of vascular plant wax is also demonstrated by the n-alkane data, where the highest contributions of vascular plant waxes to the fine particulate carbonaceous aerosol fraction occur during late summer and early fall. Biogenic residues contribute the major resolved organic acids present based on the n-alkanoic acid homologue data.