It was estimated that the eruption of the Mount Pinatubo volcano resulted in the injection of 20 million metric tons of \(S O_{2}\) into the atmosphere. Most of this \(S O_{2}\) underwent oxidation to \(S O_{3},\) which reacts with atmospheric water to form an aerosol. (a) Write chemical equations for the processes leading to formation of the aerosol. (b) The aerosols caused a \(0.5-0.6^{\circ} \mathrm{C}\) drop in surface temperature in the northern hemisphere. What is the mechanism by which this occurs? (c) The sulfate aerosols, as they are called, also cause loss of ozone from the stratosphere. How might this occur?

First, we'll start with the oxidation of \(SO_2\) to \(SO_3\). The chemical equation for this process is as follows: \( 2 \: SO_2 + O_2 \rightarrow 2 \: SO_3 \) Next, we have the reaction between \(SO_3\) and atmospheric water (H\(_2\)O) to form the aerosol, which is essentially sulfuric acid (H\(_2\)SO\(_4\)). The chemical equation for this process is: \( SO_3 + H_2O \rightarrow H_2SO_4 \) These two reactions are responsible for the formation of sulfate aerosols from the volcanic eruption.

The sulfate aerosols formed from the volcanic eruption are responsible for the \(0.5-0.6^{\circ}C\) drop in surface temperature in the northern hemisphere. This occurs due to the reflective properties of these aerosols, which causes them to reflect a significant amount of sunlight back into space before it can reach and warm the Earth's surface. As a result, the overall amount of sunlight reaching the Earth's surface is reduced, leading to a cooling effect. This mechanism, called the albedo effect, is responsible for the decrease in surface temperature observed after the Mount Pinatubo eruption.

The sulfate aerosols can cause a loss of ozone (O\(_3\)) from the stratosphere due to their role in promoting the formation of stratospheric clouds. These clouds provide a surface for heterogeneous chemical reactions to occur, which can involve the conversion of stable chlorine-containing compounds into reactive forms that can participate in ozone-depleting reactions. Specifically, reactions on the surface of sulfate aerosols can convert chlorine reservoir species, such as hydrogen chloride (HCl) and chlorine nitrate (ClONO\(_2\)), into active forms like chlorine radicals (Cl) that can destroy ozone. The chemical reactions involved in this process can be summarized as follows: 1. Heterogeneous reaction on the surface of sulfate aerosols: \( HCl + ClONO_2 \rightarrow Cl_2 + HNO_3 \) 2. Photodissociation of Cl\(_2\) into Cl radicals: \( Cl_2 + hv \rightarrow 2 \: Cl \) 3. Ozone destruction by Cl radicals: \( Cl + O_3 \rightarrow ClO + O_2 \) \( ClO + O \rightarrow Cl + O_2 \) Through these reactions, sulfate aerosols can contribute to the depletion of the ozone layer in the stratosphere.