For a better understanding of the air mass exchange processes between the surface and free atmosphere in the Himalayas, a Himalayan exchange between the surface and troposphere 2007 (HEST2007) campaign was carried out in the Rongbuk Valley, on the northern slope of Mt. Qomolangma, in June 2007. The wind, temperature and radiation conditions were measured during the campaign. Using these observation data, together with the NCEP/NCAR reanalysis data, the air mass exchange between the inside of the valley and the outside of the valley is quantitatively estimated, based on a closed-valley method. The air mass is strongly injected into the Rongbuk Valley in the afternoon, which dominates the diurnal cycle, by a strong downward along-valley wind, with a maximum downward transfer rate of 9.4 cm s?1. The total air volume flux injected into the valley was 2.6×1011 m3 d?1 in 24 hours in June 2007, which is 15 times the total volume of the valley. The air mass transfer into the valley also exhibited a clear daily variation during the HEST2007 campaign, which can be affected by the synoptic situations through the adjustment of local radiation conditions.