Balloon observations of organic and inorganic chlorine in the stratosphere: The role of HClO_4 production on sulfate aerosol

摘要

Simultaneous observations of stratospheric organic and inorganic chlorine were made in September 1993 out of Fort Sumner, New Mexico, using the JPL balloon-borne MkIV interferometer. Between 15 and 20 km, a significant fraction (20–60%) of the inorganic chlorine could not be accounted for by the sum of measured HCl, ClONO_2, and HOCl. Laboratory measurements of the reaction of ClO radicals on sulfuric acid solutions have indicated that, along with HCl, small amounts of perchloric acid, HClO_4, were formed. Very little is known about the fate of HClO_4 in the stratosphere and we use a photochemical box model to determine the impact of this new species on the partitioning of inorganic chlorine in the stratosphere. Assuming that HClO_4 is photochemically stable, it is shown that in the enhanced aerosol loading conditions resulting from Mt. Pinatubo's eruption, HClO_4 could represent a significant reservoir of chlorine in the lower stratosphere, sequestering up to 0.2 ppbv (or 50%) of the total inorganic chlorine at 16 km. The occurrence of this new species could bring to closure the inorganic chlorine budget deficiency made apparent by recent ER-2 aircraft in situ measurements of HCl.