In situ scanning tunneling microscopy (STM) is utilized to image the structures formed by neat dimethyl sulfoxide (DMSO) on Au surfaces at room temperature. The STM reveals that DMSO forms ordered arrays of chains on Au(111) lattices, but is substantively disordered on the other low Miller index faces of Au. The chain structures, which are insensitive to added water, non-oxidizing electrolytes, and DMSO preparation, are interpreted in terms of a head-to-tail association of DMSO with itself and the interchain repulsions also observed are interpreted in terms of dipolar misfit between the chains. Addition of nitric acid to the neat DMSO liquid results in the rapid formation of an entirely different structure resulting from the creation of the hydroxy sulfonium nitrate. While the neat DMSO structure evinces a low and nearly charge independent interfacial capacity, the capacity with added nitric acid is an order of magnitude higher and exhibits considerable structure over the potential range studied. The results from neat DMSO in ambient are compared with previous results obtained in the ultrahigh vacuum environment.