Air Quality Model Evaluation Data for Organics. 4. C_2−C_(36) Non-Aromatic Hydrocarbons

Abstract

The concentrations of 143 non-aromatic hydrocarbons are quantified in 36 samples (32 urban and 4 background) collected during a severe Los Angeles area photochemical smog episode. Gas phase, semivolatile, and particle phase organic compounds are viewed simultaneously across the carbon number range from C_2 to C_(36). Compound classes studied include the n-alkanes, branched alkanes, n-alkenes, branched alkenes, diolefins, alkynes, saturated cyclic hydrocarbons, unsaturated cyclic hydrocarbons, biogenic hydrocarbons, petroleum biomarkers, and the unresolved complex mixture contained within the semivolatile and particle phase organics samples. The abundance of the n-alkanes falls almost exponentially with increasing n-alkane carbon number, and the distribution of the n-alkanes between the gas and particle phases follows vapor/particle partitioning theory. The concentrations of individual low molecular weight alkenes decline during transport across the urban area in about the order expected given their initial rates of reaction with the hydroxyl radical. Petroleum biomarker concentrations that act as tracers for particulate organics emitted from vehicle exhaust have declined substantially between 1982 and 1993, reflecting the increased penetration of catalyst-equipped cars into the vehicle fleet. The most pronounced change in vapor phase non-aromatic hydrocarbons concentrations between 1987 and 1993 is a reduction in the concentration of the lightest blending components of gasoline (e.g., butanes), reflecting new regulations that limit the Reid vapor pressure of gasoline.

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