The importance of atmospheric ozone and hydrogen peroxide in oxidising sulphur dioxide in cloud and rainwater

doi:10.1016/j.atmosenv.2007.10.065

Atmospheric Environment

Volume 41, Supplement, 2007, Pages 154-168

https://doi.org/10.1016/j.atmosenv.2007.10.065 Get rights and content

Abstract

The process by which sulphur dioxide is oxidised in atmospheric droplets has been studied in laboratory experiments designed to collect a large amount of chemical data pertinent to the atmospheric situation. Thus the oxidation of sodium sulphite solutions by oxygen, ozone and hydrogen peroxide has been studied at different pH's and temperatures. In all cases the reaction is first order with respect to sulphite ion but the order with respect to oxidant differs. For oxygen the order is zero whereas the order for ozone and hydrogen peroxide is one. Varying the hydrogen ion concentration has little effect on the oxygen reaction rate between pH 6 and 9; the ozone reaction rate is inversely proportional to the square root of the hydrogen ion concentration and the hydrogen peroxide rate is almost directly proportional to the hydrogen ion concentration. These last two observations are very important since in the case of ozone it indicates that the reaction proceeds via a free radical mechanism involving hydroxyl radicals and in the case of hydrogen peroxide it is the only oxidation process of sodium sulphite so far investigated that shows a positive response to the presence of hydrogen ions.

The experimental data was used to calculate the rate of sulphate formation in water droplets under atmospheric conditions for each of the three oxidants. If it is assumed that the ozone and hydrogen peroxide gas phase concentrations are initially 50 parts in 10⁹ and 1 part in 10⁹ by volume respectively, then the rates of sulphate formation are equal in cloud water at pH 5.8. Above this pH the ozone reaction is faster and below it the hydrogen peroxide reaction is faster due to the positive catalysis by hydrogen ions; the oxygen rate is unimportant by comparison at all pH's below 7. The rate of hydrogen peroxide reaction is such that substantial amounts of sulphate can still be formed rapidly in water droplets at pH values from 3 to 5, and thus this process will be very important in creating acidity in rainwater.

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The importance of atmospheric ozone and hydrogen peroxide in oxidising sulphur dioxide in cloud and rainwater

Abstract

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Planet. Space Sci.

Atmospheric Environment

The kinetics and mechanisms of hydroxide ion catalysed ozone decomposition in aqueous solution

Am. chem. Soc. J.

Z. phys. Chem.

Washout of tritiated water vapour by rain

Int. J. Air Wat. Pollut.

Aerosol formation from sulphur dioxide in the presence of ozone and olefinic hydrocarbons

J. Chem. Soc. Faraday Trans.

The mathematics of diffusion

Tracer experiments with ozone as oxidising agent in aqueous solution

Inorg. Chem.

The rate of oxidation of sulphite ions by oxygen

Am. chem. J.

Some fog droplet size distributions obtained with an impaction method

Q. JI. R. met. Soc.