High concentration of surface ozone observed along the Khumbu Valley Nepal April 2007

Increasing air pollution in Southeast Asia has the potential for dramatic impacts on the population and climate in relatively pristine regions such as the Himalaya. Recent measurements near Mount Everest indicate the presence of elevated levels of ozone at elevations from 5000m to 9000m that are the result of both the long‐range transport of tropospheric pollutants from Southeast Asia as well as the descent of ozone‐rich stratospheric air. Here we report on the first surface ozone concentration transect in the Mount Everest region. The data collected at elevations from 2900m to 5200m indicate an increase in concentration with height as well as 8‐hour average exposures in excess of 140ppb. Satellite data and meteorological diagnostics suggest a stratospheric source for the high levels observed. The majority of values observed exceed guidelines for human exposure and therefore are of a magnitude to suggest that they are of physiological relevance.