Question

A student states that sulfates are bad for our planet because they warm the planet. Now that you have a much greater understanding of the chemistry of various molecules, please help enlighten this student.

Answer 1

Sulfur dioxide comes from both related to human activities and natural sources. Burning coal and other fossil fuels is the largest source of sulfur dioxide from human activities. Volcanoes and forest fires are the major natural contributors. Although sulfur dioxide is of interest as a pollutant, our primary emphasis here is to explore its role in climate change. Once in the atmosphere, sulfur dioxide can easily form sulfate ions, negatively charged particles made of up of sulfur and oxygen atoms. Because of their negative charge, sulfate ions readily combine with water vapor in the atmosphere to form small droplets of sulfuric acid (H2SO4).

When a volcano erupts huge amounts of sulfur dioxide are spewed into the stratosphere and converted to sulfates. Unlike sulfates formed at lower altitudes, which are removed from the atmosphere in just a few weeks through settling and precipitation, these aerosols (mainly tiny droplets of sulfuric acid) stay in the atmosphere for about two years. They reflect incoming solar radiation back into space,absorb both incoming solar radiation and outgoing infrared radiation thereby reducing the amount of energy reaching the lower atmosphere and Earth's surface. The net effect is a cooling of the lower atmosphere and Earth's surface.

Volcanic eruptions are thought to have considerable impact on global climate. Following the eruption of Mount Pinatubo in 1991, a cooling trend that lasted through 1993 was attributed to the sulfuric acid aerosols that persisted in the stratosphere. Similar cooling followed the 1883 eruption of Krakatoa and the "Year without a summer" followed the eruption of Tambora in 1815. The potential cooling effect of stratospheric sulfates is of great interest to scientists exploring possible geoengineering methods for climate intervention.

Many scientists believe the continuous emission of sulfates in the past offset the effects of increasing greenhouse gases, masking their warming effect. Today, with uneven concentrations of sulfates around the world, the effects on climate change are very complex.