Approximately 236,000 single particle mass spectra were collected throughout the duration of the Pittsburgh Supersite experiment using the third-generation rapid single particle mass spectrometer (RSMS-3). The instrument was operated semicontinuously for 306 days, sampling particles with aerodynamic diameters in the range of 30–1100 nm and collecting both positive and negative ion spectra, particle size, and time of detection for each particle measured. The entire data set has been fully processed and analyzed. Spectra have been clustered into 20 distinct particle classes on the basis of the distribution of their positive ion mass peaks. Negative ion spectra were classified independently within each positive ion class. Frequency of occurrence versus particle size, month of the year, and wind direction has also been calculated for the full data set, as well as within each class. Results indicate a rich array of multicomponent ultrafine particles composed primarily of carbon and ammonium nitrate. Approximately 54% of all the particles measured fell into the carbonaceous ammonium nitrate (CAN) class. These particles were observed in all size bins and from most wind directions for the entirety of this study. Ubiquitous sources throughout the area, including vehicular emissions and secondary organic aerosol formation, are considered to be responsible for a larger fraction of these particles. In terms of particle number, metal containing aerosol dominated the remainder of the particle classes identified. These particles were rich in K⁺, Na⁺, Fe⁺, and Pb⁺ and to a lesser extent, Ga⁺ and Zn⁺. They tended to be smaller in size and were highly correlated with specific wind directions, facilitating the isolation of specific sources.