Diesel particulate matter (PM) was collected at different tailpipe positions where the sampling temperature was different. The PM samples were pretreated in air at high temperature until 40% mass loss. Then, the partially oxidized PM samples were aged in air for 40 days, and the physicochemical properties of partially oxidized PM before and after aging in air were tested. The results showed that the oxidation activity of partially oxidized PM was appreciably restored by aging in air. The morphology, diameter distribution of primary particles, and nanostructures of partially oxidized PM changed slightly after aging in air. The amorphous carbon adsorbing on PM surface were faintly observed through high-resolution transmission electron microscope images. The adsorption of oxygen-containing functional groups (carbonyl and hydroxy) and organic compounds were evidenced through Fourier transform infrared spectroscopy and Raman parameters A(D3)/A(G). The crystallite size calculated using Raman parameter decreased slightly after aging in air.