AIR-QUALITY MODEL EVALUATION DATA FOR ORGANICS .4. C-2-C-36 NONAROMATIC HYDROCARBONS

The concentrations of 143 non-aromatic hydrocarbons are quantified in 36 samples (32 urban and 4 background) collected during a severe Los A ngeles area photochemical smog episode. Gas phase, semivolatile, and p article phase organic compounds are viewed simultaneously across the c arbon number range from C-2 to C-36. Compound classes studied include the n-alkanes, branched alkanes, n-alkenes, branched alkenes, diolefin s, alkynes, saturated cyclic hydrocarbons, unsaturated cyclic hydrocar bons, biogenic hydrocarbons, petroleum biomarkers, and the unresolved complex mixture contained within the semivolatile and particle phase o rganics samples. The abundance of the n-alkanes falls almost exponenti ally with increasing n-alkane carbon number, and the distribution of t he n-alkanes between the gas and particle phases follows vapor/particl e 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 tile hy droxyl radical. Petroleum biomarker concentrations that act as tracers for particulate organics emitted from vehicle exhaust have declined s ubstantially between 1982 and 1993, reflecting the increased penetrati on of catalyst-equipped cars into the vehicle fleet. The most pronounc ed change in vapor phase non-aromatic hydrocarbons concentrations betw een 1987 and 1993 is a reduction in the concentration of the lightest blending components of gasoline (e.g., butanes), reflecting new regula tions that limit the Reid vapor pressure of gasoline.