Chemical composition of PM10 and PM1 at the high-altitude Himalayan station Nepal Climate Observatory-Pyramid (NCO-P) (5079 m a.s.l.)

. We report chemical composition data for PM 10 and PM 1 from the Nepal Climate Observatory-Pyramid (NCO-P), the world’s highest aerosol observatory, located at 5079 m a.s.l. at the foothills of Mt. Everest. Despite its high altitude, the average PM 10 mass apportioned by the chemical analyses is of the order of 6 µg m − 3 (i.e., 10 µg/scm), with almost a half of this mass accounted for by organic matter, elemental carbon (EC) and inorganic ions, the rest being mineral dust. Organic matter, in particular, accounted for by 2.0 m 3.6 µg/scm) on a yearly basis, and it is by far the major PM 10 component beside mineral oxides. Non-negligible concentrations of EC were also observed (0.36 µg/scm), confirming that light-absorbing aerosol produced from combustion sources can be efficiently transported up the altitudes of Himalayan glaciers. The concentrations of carbonaceous and ionic aerosols follow a common time trend with a maximum in the premonsoon season, a minimum during the monsoon and a slow recovery during the postmonsoon and dry seasons, which is the same phenomenology observed for other Nepalese Himalayan sites in previous studies. Such seasonal cycle can be explained by the of of the effect of of and upslope that the valley

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