Electrolyte effects on aqueous atmospheric oxidation of sulphur dioxide by ozone

Abstract

The kinetics of sulphur(IV) oxidation by ozone in an aqueous solution were studied in various supporting electrolytes (NaClO4, NaCl, NH4ClO4, Na2SO4), using the stopped flow method. The rate data in perchlorate medium (chosen as reference electrolyte) are empirically correlated by the following expression: r = −d[O3]/dt = k [O3] [S(IV)] [H+]−1/2. For each supporting electrolyte studied, the rate constant varies linearly with the ionic strength. The value of the rate constant is extrapolated to zero ionic strength (1.65 × 104 mol−0.5 L0.5 s−1). The rate constants are shown to be higher mainly when ammonium chloride and sodium sulphate are added to the solution. The effect of temperature is studied between 13 ° and 28 °C. The reaction rate is unaffected by the trace presence of metal ion (Mn2+, Fe2+, Cu2+, Fe3+, Cr3+). The rate of oxidation of dissolved SO2 by O3, in water droplets under atmospheric conditions (presence of [H2O2] = 4.31 × 10−5 mol L−1 and [O3] = 1.17 × 10−9 mol L−1), is calculated as a function of [H+] and compared to the oxidation by H2O2. At zero ionic strength the ozone reaction becomes faster than hydrogen peroxide reaction above −log [H+] = 4.70. This effect appears at higher H+ concentration when the ionic strength increases (−log [H+] = 3 in 4 mol L−1 NaCl or 2 mol L−1 Na2SO4).

The acidity of atmospheric particles and clouds

“…Meanwhile, sulfate formation is a major source of acidity in aerosols, fog droplets, and cloud droplets (Calvert et al, 1985). In the absence of buffering, S(IV)→S(VI) oxidation pathways which are more effective at higher pH, such as oxidation of SO 2− 3 by O 3 (Maahs, 1983;Lagrange et al, 1994) or NO 2 (Lee and Schwartz, 1983;Clifton et al, 1988), will become quenched with increasing sulfate production ( Fig. 9, Supplement Sect.…”

“…Smaller particles, typically made up of sulfate, nitrate, ammonium, and organic species, tend to be more acidic . Given that the composition of the CCN varies with size, then the fog/cloud solute composition will vary with drop size as observed in a variety of clouds and fogs (Noone et al, 1988;Ogren et al, 1989;Munger, 1989;Bator and Collett Jr., 1997;Laj et al, 1998;van Pinxteren et al, 2016;Moore et al, 2004;Guo et al, 2012a;Herckes et al, 2013).…”

Effects of aqueous organosulfur chemistry on particulate methanesulfonate to non–sea salt sulfate ratios in the marine atmosphere

“…Potentially important atmospheric aqueous phase oxidants include O 3 , H 2 O 2 , HO 2 , OH, SO 4 − , Cl, Cl 2 − and NO 3 . Studies have found that O 3 and H 2 O 2 are the oxidants that are primarily responsible for aqueous phase SO 2 oxidation [ Botha et al , 1994; Erickson et al , 1977; Hoffmann , 1986; Kreidenweis et al , 2003, and references therein; Lagrange et al , 1994; Nahir and Dawson , 1987]. Two studies of the O 3 + DMS reaction [ Gershenzon et al , 2001; Lee and Zhou , 1994] demonstrated that the simultaneous uptake of DMS and O 3 and the subsequent surface reaction might play an important role in DMS oxidation.…”

Uptake of gas‐phase SO2 in aqueous sulfuric acid: Oxidation by H2O2, O3, and HONO

“…The rate expression is thus of the form rka, rko, and rkc refer to the fraction of S(IV) in the form SO2aq, HSO•-, and SO•-, respectively. The numerical values for the respective rate coefficients are shown inTable 2.On the other hand,Penkett et al [1979] andLagrange et al [1994], who conducted measurements in the pH range 1 to 5.5, found that the reaction rate depended on the inverse square root of the hydrogen ion concentration. Botha et al…”