High ozone concentrations (70--80 ppb) were found from late afternoon to midnight at sites at ca. 5000 m above sea level (m.a.s.l.) on Mt. Everest. Observational data suggest that katabatic wind from Mt. Everest was "pumping down" ozone-rich air from the upper troposphere. Numerical modelling demonstrates that cooling of glaciers and snow on the northern mountain slopes and heating of the valley surface play important roles in forming katabatic winds and accelerating vertical exchange between the upper atmosphere and surface air. These results suggest that the "pump-down" mechanism at high mountains covered with snow/glaciers is an important process in terrestrial intercontinental transport of ozone and atmosphere--land exchanges of masses and energy.