It was estimated that the eruption of the Mount Pinatubo volcano resulted in the injection of 20 million metric tons of SO2 into the atmosphere. Most of this SO2 underwent oxidation to SO3, which reacts with atmospheric water to form an aerosol. The aerosols caused a 0.5 to 0.6 °C drop in surface temperature in the northern hemisphere. What is the mechanism by which this occurs?

Verified step by step guidance

1. Step 1: Understand the chemical reactions involved. The sulfur dioxide (SO2) released from the volcano undergoes oxidation to form sulfur trioxide (SO3). This can be represented by the reaction: 2 SO2 + O2 → 2 SO3.
2. Step 2: Recognize the formation of aerosols. The sulfur trioxide (SO3) reacts with water (H2O) in the atmosphere to form sulfuric acid (H2SO4), which is an aerosol. This reaction can be written as: SO3 + H2O → H2SO4.
3. Step 3: Explain the role of aerosols in climate. Aerosols, such as sulfuric acid droplets, reflect sunlight back into space, reducing the amount of solar radiation that reaches the Earth's surface. This is known as the albedo effect.
4. Step 4: Connect the albedo effect to temperature change. By reflecting sunlight, aerosols decrease the energy input to the Earth's surface, leading to a cooling effect. This is why the surface temperature in the northern hemisphere dropped by 0.5 to 0.6 °C.
5. Step 5: Summarize the overall mechanism. The injection of SO2 into the atmosphere leads to the formation of reflective aerosols, which increase the Earth's albedo and result in a temporary cooling of the surface temperature.

Key Concepts

Volcanic Eruptions and Gas Emissions

Volcanic eruptions release various gases, including sulfur dioxide (SO2), into the atmosphere. SO2 can undergo chemical transformations, such as oxidation to sulfur trioxide (SO3), which is crucial for understanding the impact of volcanic activity on climate. The large quantities of SO2 emitted during eruptions can significantly influence atmospheric chemistry and climate patterns.

Aerosol Formation and Climate Effects

Aerosols are tiny particles suspended in the atmosphere that can originate from various sources, including volcanic eruptions. When SO3 reacts with water vapor, it forms sulfuric acid aerosols, which can reflect sunlight and increase cloud formation. This process leads to a cooling effect on the Earth's surface, as these aerosols scatter and absorb solar radiation, reducing the amount of heat that reaches the ground.

Radiative Forcing and Temperature Change

Radiative forcing refers to the change in energy balance in the Earth's atmosphere due to factors like greenhouse gases and aerosols. The introduction of sulfuric acid aerosols from volcanic eruptions leads to negative radiative forcing, which results in a cooling effect. This mechanism explains the observed drop in surface temperatures, as the aerosols reflect incoming solar radiation, thereby reducing the overall temperature in the affected regions.