Ozone oxidation of sulfur in sea‐salt aerosol particles during the Azores Marine Aerosol and Gas Exchange experiment

Abstract

Sea‐salt aerosol particles in the lowest tens of meters above the ocean are, typically, more than three‐fourths water on a volume basis. Calculations herein indicate that aqueous‐phase conversion of sulfur dioxide dissolved in the water associated with sea‐salt particles (sea‐salt aerosol water) supported the production of 2–8 nmol m−3 of nonsea‐salt sulfate (nssSO4=) during the Marine Aerosol and Gas Exchange (MAGE) experiment intensives. This production is based on ozone oxidation of dissolved SO2 in sea‐salt aerosol water and accounts for sulfur gas and ozone mass transfer limitations as a function of sea‐salt particle size. Measurements showed that 1–15 nmol m−3 of nssSO4= was actually present in the sea‐salt particle mode except for four enhanced concentration cases due to continental sulfur input. The range in predicted, as well as observed, nssSO4= was primarily due to variability in sea‐salt aerosol water volume. The nssSO4= produced by ozone oxidation of sulfur dioxide, being in the sea‐salt particle mode with observed volume geometric median diameter of 3.5–5 μm, is dry deposited at a fairly rapid rate. The remainder, being large‐particle cloud condensation nuclei, may contribute little to cloud albedo over the global oceans. The two papers following this one, Kim et al. (this issue) on aerosol size distribution and water content and Parfai et al. (this issue) on compositional variations of sea‐salt‐mode aerosol particles observed by electron microscopy, complement and support results presented here. All three present results of the MAGE experiment and precede a forthcoming special issue of the Journal of Geophysical Research‐Atmospheres on MAGE (B. Huebert, guest editor).

The uptake of SO2 on synthetic sea salt and some of its components

“…This is consistent with a slow reaction of S(IV) in the water layer. Sea salt is known to contain buffering species such as carbonates which can react with dissolved S(IV) [Sievering et al, , 1992[Sievering et al, , 1995 …”

“…Sulfur dioxide (SO2) in the marine boundary layer is oxidized in deliquesced sea salt aerosol with dissolved oxidants such as ozone and H202 to form S(VI) species Sievering et al, 1991Sievering et al, , 1992Sievering et al, , 1995 [Vogt et. al., 1996].…”

Multiphase chemistry of NO3 in the remote troposphere

“…Ozone efficiently oxidizes SO2 in neutral or basic sea-salt aerosols [Sievering et al, 1995]. It has also been suggested that S(IV) is oxidized via a catalytic cycle [Mozurkewich, 1995;Sander et al, 1995].…”

A new approach to studying aqueous reactions using diffuse reflectance infrared Fourier transform spectrometry: application to the uptake and oxidation of SO2 on OH-processed model sea salt aerosol

“…Dissolved S(IV) is oxidized in the aqueous phase and on the surfaces of particles by a number of oxidants, such as H 2 O 2 , O 3 , HOCl, HOBr and O 2 catalyzed by metals and perhaps by chloride ions. [50][51][52][53][54][55]57,60,71,[81][82][83][84][85][86][87][88][89][90][91][92][93][94][95] SO 2 can also be oxidized in the gas phase, mainly by OH, 96 to produce sulfuric acid which is then taken up by cloud droplets and particles; however, this is generally a minor pathway compared to aqueous oxidation. 16 In this work, we demonstrate the application of DRIFTS to studying the uptake and oxidation of gaseous SO 2 at 50% relative humidity (RH) on NaCl-MgCl 2 Á 6H 2 O salt mixtures that have been previously reacted with OH formed by the photolysis of O 3 in the presence of water vapor.…”