Atmospheric aging of internally mixed sea salt and organic particles: surprising reactivity of NaCl with weak organic acids
Poster PDF
Authors
Alexander Laskin — Purdue University
Ryan Moffet — Sonoma Technology Inc.
Mary Gilles — Lawrence Berkeley National Laboratory
Jerome D Fast — Pacific Northwest National Laboratory
Rahul Zaveri — Pacific Northwest National Laboratory
Category
Aerosol Properties
Description
Composition of internally mixed sea salt—organic particles collected on board the G-1 research aircraft during the Carbonaceous Aerosol and Radiative Effects Study (CARES)—was performed using complementary electron microscopy and X-ray spectro-microscopy techniques. Substantial chloride depletion in individual sea salt particles is reported that could not be accounted by the presumed reactivity of sea salt with atmospheric inorganic nitric and sulfuric acids. We present field evidence that sea salt components in deliquesced atmospheric particles may effectively react with dissolved organic acids, releasing HCl gas to the atmosphere and leaving particles enriched in the corresponding organic salts. Formation of the organic salts products is not thermodynamically favored in the aqueous phase. However, the surprising shift of the reaction equilibrium in the aerosolized particles is driven by high volatility of the HCl product and its efficient evaporation from particles. Similar observations were also corroborated in a set of laboratory experiments where NaCl particles mixed with organic acids were found depleted in chloride. Formation of organic salts in the aged particles of marine origin will modify their hygroscopic and optical properties and impact their subsequent atmospheric reactions, hydration behavior, and propensity to act as cloud condensation and ice nuclei.
