Stratospheric aerosol: The contribution from the troposphere

Aerosol samples collected during stratospheric flights over the midcontinental United States were analyzed by neutron activation for Na, Cl, K, Mn, Br, and Si. The flights were made in autumn and in spring along the 39°N parallel between 109° and 87°W at altitudes of 11.0, 13.4, 15.8, 18.2, and 20 km. The long sampling paths served to integrate variations in aerosol mixing ratio and composition and so give a good representation of mean aerosol composition. The elemental composition for the stratospheric aerosol is compared with that of the tropospheric aerosol, and the relative contribution of marine and continental components of the tropospheric contribution to the stratospheric aerosol is estimated. An approximately twofold excess of Cl and 200-fold excess of Br above what is consistent with the marine component of the tropospheric contribution is noted.