Composition of aerosols and cloud water at a remote mountain site (2.8 kms) in Pakistan

Abstract

Major ion and trace metal concentrations were determined in aerosols and cloud water at a site in the Himalayan Mountains of Northern Pakistan. In spite of the fact that the site is well removed from significant urban/industrial pollution sources the SO²⁻₄ concentrations in some of the samples were as high as those observed in North America. Concentrations of Se, Tl, Pb, Cl, Cd, Sb, Zn, and As in aerosols were highly enriched relative to average crustal abundances indicating significant anthropogenic contributions. Cloud water concentrations of major ions and trace elements are reported for 18 samples from six different clouds. The pH varied between 5.3 and 6.8 in spite of the fact that the SO²⁻₄ concentration approached 300 μmol in some samples, values often observed in the northeastern US. Selenium was used as a tracer to determine in-cloud production of SO²⁻₄ in these clouds and in three of the six clouds 40–60% of the observed SO²⁻₄ came from in-cloud production.