Respeciation of Organic Gas Emissions and the Detection of Excess Unburned Gasoline in the Atmosphere

The development of a set of organic gas composition profiles for key source categories is described. This information is used to recompute the organic gas emission inventory for the Los Angeles area. Comparisons are made between the revised emission inventory and ambient concentration measurements in southern California. Respeciation of the organic gas emissions results in large changes in the basinwide emissions estimates for many individual organic species, including l,3-butadiene, ethylene glycol, methanol, and cyclohexane. Significant changes are observed in the reactivity of the chemical composition profiles for individual source categories, especially for surface-coating activities and associated thinning solvent use. Receptor-modeling methods are used to identify the relative importance of major sources that contribute to atmospheric organic gas concentrations in southern California. The receptor modeling results indicate a key discrepancy between the emission inventory and ambient data: there is much more unburned gasoline in the atmosphere than is indicated in the emission inventory. These excess unburned gasoline emissions may be coming from a combination of sources including tailpipe emissions, hot-soak evaporative emissions, and fuel spillage