Understanding the changes in particle physical and chemical characteristics is critical for investigating the formation mechanisms of particles. This study conducted an observation campaign at the National Background Station on the Qinghai-Tibetan Plateau. We employed a Scanning Mobility Particle Sizer (SMPS) for measuring particle number concentration (PNC), sized from 3.85 to 478.30 nm. The observation was conducted from September 17th to October 14th, 2013, aiming to analyze particle size distributions of new particle formation (NPF) events and non-NPF in an environment free from complex human-induced disturbances, allowing for a more isolated study on the processes of particle formation and growth. We found that the NPF events occurred frequently (about 80 % days of the observation period) in this high-altitude region. Further source analysis identified four factors: nucleation sources, nucleation aging sources, combustion emissions sources, and secondary formation sources. Distinct differences existed in the diurnal variations of these factors between NPF and non-NPF periods. In summary, with the absence of significant human interference, we identified the major drivers of the four sources: 1) nucleation source was primarily driven by gaseous sulfuric acid at low wind speeds
2) the levels of O