Abstract: In order to study the particle size distribution in the middle and upper part of the atmospheric boundary layer and the relationships with air mass transport pathways, the particle size distributions in a diameter range of 14.6-660 nm were measured using a scanning mobility particle sizer (SMPS-3080) at Mountain Wudang in June 2018. The size distributions and diurnal variations of number concentrations were analyzed. PSCF and CWT were used to explore the exogenous transport pathways and potential sources of number concentrations at Mountain Wudang. The results showed that: (1) The particle concentrations ranked in the order of Aitken mode (2500 cm^-3, 48.79%) > accumulation mode (2265 cm^-3, 44.21%) > nucleation mode (359 cm^-3, 7.01%). (2) On new particle formation (NPF) days, the number concentration of nucleation mode began to rise at 10:00 and remain a relatively high level of about 2000 cm^-3 from 11:00 to 17:00. The daily variation trend of ρ(SO₂) and ρ(O₃) on NPF days was similar to the nucleation mode, indicating that the sulfuric acid formed by photochemical reactions of SO₂ and organic matter produced by VOCs and O₃ participated in the formation and growth progress of new particles. The wind speed and temperature were higher on NPF days than those on non-NPF days, while the relative humidity was lower on NPF days. (3) The aerosol observed under the influence of the eastern and local air masses was dominated by accumulation mode with number concentration of 2311 and 2596 cm^-3. The number concentrations in nucleation mode and Aitken mode were the highest under the effect of the northwest air mass and their concentrations were 806 and 3078 cm^-3, respectively. (4) The potential source analysis indicated the major source areas were Shiyan City and Xiangyang City and the value was above 840 cm^-3. The study showed that the particles of Mountain Wudang were mainly dominated by the Aitken mode, and the diurnal variation of the particle number concentration was mainly affected by the development of atmospheric boundary layer and the mountain-valley breeze. Higher concentrations of SO₂ and O₃, high temperature, low humidity and higher wind speed were conducive to the formation of new particles, and the regional transmission from surrounding cities had a great impact on Mountain Wudang.