Composition of Tropospheric Aerosols as a Function of Altitude

Abstract

A series of aerosol samples was collected using a three-stage impactor at altitudes to 10 km from locations near Scottsbluff, Neb., Death Valley, Calif., and over the Pacific Ocean about 250 km west of Santa Barbara, Calif. A few samples were obtained from other locations viz., the central Pacific, Venezuela, and Chicago, Ill. Chemical analyses were made by means of x-ray techniques. At the locations for which concentrations near the ground were measured, most average mass concentrations of the elements Cl, S, K, Ca and Ti decreased rapidly from the ground to about half or less the ground concentration at 1 km and then maintained more or less constant values up to 10 km. Low Cl concentrations (except near the ocean surface) suggest a small sea salt contribution at the higher altitudes. The soil component of the aerosol believed to Be indicated by uniform average mass ratios of Ti/SI, K/Si and Ca/Si was quite constant with respect to altitude and location. Ratios of these latter elements were found to be distributed virtually log normally. The distribution of the ratios Cl/Si and S/Si was not consistently log normal, presumably because of contributions from pollution sources of these elements. Averaged concentrations at all altitudes for the locations sampled ranged from 0.18?1.52 µg m?3 for Cl, 0.03?0.31 µg m?3 for S, 0.03?0.60 µg m?3 for K, 0.01?1.27 µg m?3 for Na, 0.04?0.76 µg m?3 for Si, 0.02?2.22 µg m?3 for Ca, and 0.004?0.13 µg m?3 for Ti. Mass median diameters ?0.3 ?m were indicated for most of the determined elements at the altitudes sampled.