The main objectives of this Cooperative Agreement were to use a new regional elemental tracer technique to search for the signature(s) of Midwestern aerosol, to use the resulting signature(s) to determine whether mid western aerosol reaches the Northeast during summer, and to compare the transport of perfluorocarbon tracer gases with that of regional aerosol during the CAPTEX experiment. Secondary goals included testing various statistical aspects of the tracer system and evaluating stability of signatures during transport. From samples in Ohio and Pennsylvania, two Midwestern signatures were found and later used to show that aerosol is routinely transported from Midwest to Northeast in distinct pulses of 2-8 days. The tracer system was validated qualitatively during CAPTEX '83, where pulses of tracer gas from Ohio appearing in New England were always linked with pulses of Midwestern aerosol. Factor and cluster analysis were found to be only moderately useful for determining regional signatures. In eastern north America, As/Se, noncrustal V/Se, and In/Se have greater tracer power than Sb/Se, Zn/Se, and noncrustal Mn/Se. Long-term apportionments showed that most elements in the Northeast come mostly from the Northeast, that As and In have large components from Canadian smelters, and that sulfate and Se have large components from the Midwest. Results for sulfate generally agreed within 20% with models and directional studies. Regional signatures were found to be stable: during episodic transport from Midwest to Northeast, all four quantifiable elemental ratios changed by less than 25% on the average. Regional least-squares apportionments were found to be insensitive to a variety of factors such as weighting scheme, scales of signatures, random elemental perturbations, duration of samples, and local sources of V.