The geochemical cycling of reactive chlorine through the marine troposphere

Abstract

Heterogeneous reactions involving sea‐salt aerosol in the marine troposphere are the major global source for volatile inorganic chlorine. We measured reactant and product species hypothesized to be associated with these chemical transformations as a function of phase, particle size, and altitude over the North Atlantic Ocean during the summer of 1988. Concentrations of HCl were typically less than 1.0 ppbv near the sea surface and decreased with altitude and with distance from the U.S. east coast. Concentrations of Cl volatilized from aerosols were generally equivalent to the corresponding concentrations of HCl and ranged from less than detection limits to 125 nmol m−3 STP. Highest absolute and percentage losses of particulate Cl were typically associated with elevated concentrations of anthropogenic combustion products. Concentrations of product nss SO42− and N03− in coarse aerosol fractions indicate that on average only 38% of measured Cl− deficits could be accounted for by the combined effects of acid‐base desorption and reactions involving nonacidic N gases. We hypothesize a mechanism for the Cl loss initiated by reaction of O3 at sea‐salt aerosol surfaces, generating Cl2 followed by rapid photochemical conversion of Cl2 to HCl via Cl atoms (Cl˙) and eventual recapture of HCl by the aerosol. Simulations with a zero‐dimension (0‐D) photochemical model suggest that oxidation by Cl˙ may be an important tropospheric sink for dimethyl sulfide and hydrocarbons. Under low‐NOx conditions, the rapid cycling of reactive Cl would provide a catalytic loss mechanism for O3, which would possibly explain the low O3 concentrations often observed above the world's oceans.

Estimating N<sub>2</sub>O<sub>5</sub> uptake coefficients using ambient measurements of NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, ClNO<sub>2</sub> and particle-phase nitrate

“…Chloride concentrations exceeding 1 M may be found in sea-salt particles, which have [Cl] close to 5 M when freshly generated (Sander and Crutzen, 1996). While the sodium content of the particles is conserved during transport, there are mechanisms by which chloride may be lost to the gas-phase including acid displacement of HCl following uptake of HNO 3 or H 2 SO 4 as well as reactive losses via uptake of N 2 O 5 and other inorganic trace gases and radicals (Keene et al, 1990(Keene et al, , 1999von Glasow et al, 2001). The presence of chloride in non-marine aerosol is related to the uptake of HCl to particles and formation of ammonium chloride, where the HCl may be either of anthropogenic or marine origin.…”

Inland Concentrations of Cl2 and ClNO2 in Southeast Texas Suggest Chlorine Chemistry Significantly Contributes to Atmospheric Reactivity

“…Numerous mechanisms have been proposed to explain the exact pathway for the heterogeneous formation of Cl2. For example, the reaction of gas phase O3 at the particle surface has been suggested [31,32]. …”

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.…”