Aerosols are tiny solid or liquid particles in the atmosphere. They’re usually too small to see with the naked eye. The amount of aerosols in the atmosphere has been increasing for decades.1

Human activity can produce aerosols. However, they also arise from natural phenomena, such as volcanoes and dust storms Aerosols contain many different materials including smoke, dust and sea salt. Some aerosols contain sulfuric acid, which is created when sulfur dioxide undergoes chemical reactions in the atmosphere. Volcanoes emit sulfur dioxide, and people create it when they burn fossil fuels or vegetation.

SmokestackMost aerosols make the climate cooler by reflecting sunlight back into space. Sulfuric acid in the atmosphere plays an important role in global cooling. It attracts water, so when aerosols containing sulfuric acid enter clouds, they encourage more cloud droplets to form. This makes the clouds brighter, so they reflect more sunlight. Aerosols reflect about one fourth of the Sun’s energy back into space.2

In 1991, when Mount Pinatubo in the Philippines erupted, it released so much sulfur dioxide into the stratosphere that global temperatures dropped by 0.6 degrees centigrade for close to two years.

The cooling effect of aerosols in the atmosphere could be offsetting the warming effect of greenhouse gases. However, unlike greenhouse gases, such as carbon dioxide, which stay in the atmosphere for decades, aerosols usually stay in the lower atmosphere for only a few days or weeks and then get washed away by precipitation.

This means that human made aerosols aren’t distributed evenly over the Earth. They tend to be concentrated over the industrialized regions where they were produced, so these areas benefit from their cooling effects.  Less industrialized regions aren’t cooled in this way; however, they suffer the effects of global warming.

Not all aerosols reflect sunlight and make the climate cooler. Darker-colored aerosols, such as those from soot, which contains large amounts of carbon, absorb it. These aerosols make the climate warmer.

When dark aerosols are deposited on ice, they make the ice less reflective, so the surface warms. Carbon deposits from wildfires and industrial pollution are probably contributing to the Arctic becoming warmer and increasing the rate at which Arctic ice is melting.3

Aerosols and Clouds

In addition to causing clouds to become brighter and reflect more sunlight, aerosols affect the amount of precipitation clouds produce. Scientists aren’t exactly sure how clouds affect the hydrologic cycle. However, research shows that aerosols seem to suppress precipitation and hinder cloud formation.4

Aerosols, Health and Climate

Aerosols affect air quality and can have a deleterious effect on health, not just in people, but in all living things, including domestic animals and crops. They can affect the ability of plants to perform photosynthesis, which plays an important role in regulating climate.

Learn more about the Earth’s atmosphere.

1Aerosols, Climate and Air Quality, Earth Systems Research Laboratory, National Oceanic & Atmospheric Administration.