AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Rapid Chlorine Depletion in Nascent Sea Spray Aerosol by Condensed-Phase Aging Mechanisms
Noopur Sharma, SWARUP CHINA, Kuo-Pin Tseng, Daniel Knopf, Josephine Aller, Pacific Northwest National Laboratory
Abstract Number: 661 Working Group: Remote and Regional Atmospheric Aerosol
Abstract Sea spray aerosol (SSA) are produced at the sea surface by wave breaking and suspended into the marine boundary layer as a result of wind activity. In the atmosphere, these particles undergo multiphase chemical reactions leading to the depletion of their chloride ions, that have profound consequences on their physio-chemical properties. The aging process plays an important role in troposphere by contributing as a source of molecular chlorine in the atmosphere. As chlorine is depleted, particles undergo phase state and morphological transformations. Acidification of SSA by HNO3 via displacement of the chlorine with nitrate ions is well established. Recently, it has been shown that organic acids, e.g. present as a coating of secondary organic aerosol, can also induce depletion of chlorine and the extent of reaction depends upon several factors like particle composition and acid strength, viscosity, mixing state, relative humidity, temperature and reaction time.
In this study, freshly generated nascent SSA samples collected during WACSII cruise from the western North Atlantic and Sargasso Sea in May 2014 onto substrates by impaction, were investigated for potential chlorine depletion and morphological changes. An array of micro-spectroscopy techniques: computer-controlled scanning electron microscopy coupled with energy dispersive X-ray microanalysis, scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure analysis, and nano-secondary ion mass spectrometry were used to obtain the physio-chemical characteristics of individual particles. Our results indicate noticeable organic coating of the salt core and particles smaller than 1µm undergo considerable depletion of chlorine, despite their very brief exposure to ambient and humidified conditions. Here, we present the characterization of the chemistry at individual particle level, to improve the understanding of the aging process in sea salt particles and its characteristic timescales relevant for gas and particle chemistry in marine boundary layer.