Aerosols and their impact on climate


The brightest sunsets, cloudy skies, and days when everyone is coughing all have something in common: it’s all because of aerosols, tiny particles floating in the air. Aerosols can be tiny droplets, dust particles, bits of fine black carbon, and other substances that float in the atmosphere and change the entire energy balance of the planet.

Aerosols have a huge impact on the planet’s climate. Some, like black and brown carbon, warm the Earth’s atmosphere, while others, like sulfate droplets, cool it. Scientists believe that in general, the entire spectrum of aerosols eventually slightly cools the planet. But it is still not entirely clear how strong this cooling effect is and how much it progresses over the course of days, years or centuries.

What are aerosols?

The term “aerosol” is a catch-all for the many kinds of small particles that are suspended throughout the atmosphere, from its outermost edges to the planet’s surface. They can be solid or liquid, infinitesimal or large enough to be seen with the naked eye.

“Primary” aerosols, such as dust, soot or sea salt, come directly from the planet’s surface. They are lifted into the atmosphere by gusty winds, soared high into the air by exploding volcanoes, or shot out of smokestacks and fires. “Secondary” aerosols are formed when various substances floating in the atmosphere—for example, organic compounds released by plants, droplets of liquid acid, or other materials—collide, resulting in a chemical or physical reaction. Secondary aerosols, for example, create the haze from which the Great Smoky Mountains in the United States are named.


Aerosols are emitted from both natural and anthropogenic sources. For example, dust rises from deserts, dry riverbanks, dry lakes, and many other sources. Atmospheric aerosol concentrations rise and fall with climatic events; during cold, dry periods in the planet’s history, such as the last ice age, there was more dust in the atmosphere than during warmer periods of Earth’s history. But people have influenced this natural cycle – some parts of the planet have become polluted by the products of our activities, while others have become excessively wet.

Sea salts are another natural source of aerosols. They are blown out of the ocean by wind and sea spray and tend to fill the lower parts of the atmosphere. In contrast, some types of highly explosive volcanic eruptions can shoot particles and droplets high into the upper atmosphere, where they can float for months or even years, suspended many miles from the Earth’s surface.

Human activity produces many different types of aerosols. The burning of fossil fuels produces particles well known as greenhouse gases – thus all cars, aircraft, power plants and industrial processes produce particles that can accumulate in the atmosphere. Agriculture produces dust as well as other products such as aerosol nitrogen products that affect air quality.

In general, human activities have increased the total amount of particles floating in the atmosphere, and now there is about twice as much dust as it was in the 19th century. The number of very small (less than 2,5 microns) particles of a material commonly referred to as “PM2,5” has increased by about 60% since the Industrial Revolution. Other aerosols, such as ozone, have also increased, with serious health consequences for people around the world.

Air pollution has been linked to an increased risk of heart disease, stroke, lung disease, and asthma. According to some recent estimates, fine particles in the air were responsible for more than four million premature deaths worldwide in 2016, and children and the elderly were the hardest hit. Health risks from exposure to fine particles are highest in China and India, especially in urban areas.

How do aerosols affect the climate?


Aerosols affect climate in two main ways: by changing the amount of heat that enters or exits the atmosphere, and by affecting how clouds form.

Some aerosols, like many types of dust from crushed stones, are light in color and even slightly reflect light. When the sun’s rays fall on them, they reflect the rays back from the atmosphere, preventing this heat from reaching the Earth’s surface. But this effect can also have a negative connotation: the eruption of Mount Pinatubo in the Philippines in 1991 threw into the high stratosphere an amount of tiny light-reflecting particles that was equivalent to an area of ​​​​1,2 square miles, which subsequently caused a cooling of the planet that did not stop for two years. And the Tambora volcano eruption in 1815 caused unusually cold weather in Western Europe and North America in 1816, which is why it was nicknamed “The Year Without a Summer” – it was so cold and gloomy that it even inspired Mary Shelley to write her Gothic novel Frankenstein.

But other aerosols, such as small particles of black carbon from burned coal or wood, work the other way around, absorbing heat from the sun. This ultimately warms the atmosphere, although it cools the Earth’s surface by slowing down the sun’s rays. In general, this effect is probably weaker than the cooling caused by most other aerosols – but it certainly has an effect, and the more carbon material accumulates in the atmosphere, the more the atmosphere warms up.

Aerosols also influence the formation and growth of clouds. Water droplets easily coalesce around particles, so an atmosphere rich in aerosol particles favors cloud formation. White clouds reflect incoming sun rays, preventing them from reaching the surface and warming the earth and water, but they also absorb the heat constantly radiated by the planet, trapping it in the lower atmosphere. Depending on the type and location of the clouds, they can either warm the surroundings or cool them.

Aerosols have a complex set of different impacts on the planet, and humans have directly influenced their presence, quantity, and distribution. And while climate impacts are complex and variable, the implications for human health are clear: the more fine particles in the air, the more it harms human health.

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