Tristan is a student at the Wageningen University with its main focus on atmospheric science.
What are Atmospheric Aerosols?
Atmospheric aerosols are tiny particles present in the atmosphere with a size range in the order of 10-9 to 10-7 m. The figure below shows multiple sources and sinks of the aerosols. Furthermore, it shows that aerosols can encounter many different processes in the atmosphere. This variety in options for the aerosol is why many researchers are focused on finding out how aerosols exactly behave in the atmosphere.
This leads to the question, what makes the aerosols so important that so many researchers are researching the behaviour of aerosols. Or in other words, how do the aerosols impact the earth's climate? Which types of aerosols are of importance? Can we potentially use aerosols to our advantage in order to mitigate climate change?
What is the Impact of Atmospheric Aerosols on the Earth's Climate?
The atmospheric aerosols can potentially have three large impacts on the climate on earth (depending on the type of aerosol). The first two impacts are direct, while the third is an indirect impact on the earth's climate.
- The aerosols can reflect the incoming solar radiation. When the aerosol content would increase, the amount of reflection would increase as well. This results in a net cooling effect of the earth.
- Depending on the chemical composition of an aerosol, an aerosol can also absorb instead of reflecting the incoming solar radiation. In case an aerosol would absorb the incoming solar radiation, the atmospheric layer in which the aerosols reside would heat up. So aerosols that absorb incoming radiation cause potential warming of the earth's climate.
- The presence of aerosol can influence cloud development and thereby influence the cloud characteristics such as the cloud albedo. If an aerosol would lower the cloud albedo, less radiation is reflected, which would lead to a warming of the climate. It is essential to note that the impact of an aerosol on the clouds depends on specific aerosol properties. This means that different types of aerosols can have different impacts on cloud characteristics such as the cloud albedo.
The Three Most Important Types of Aerosols
Based on research by NASA, three types of aerosols can be defined that have a significant impact on the earth's climate.
- Volcanic aerosols
- Desert dust
- Anthropogenic aerosols
These three types of aerosols will be discussed in more detail in the paragraphs below.
The Volcanic Aerosols
A volcanic eruption leads to the natural emission of sulphur dioxide (SO2), hydrochloric acid (HCl) and ashes. Two chemicals and ashes that can potentially influence the radiation balance and thereby the climate on earth.
The first chemical, the sulphur dioxide will be transformed through chemical reactions into sulphuric acid (H2SO4). In turn, the sulphuric acid can transform into multiple other chemicals that will ultimately form new aerosols that have an average residence time in the atmosphere of multiple years. Together with the ashes emitted by the volcano, these newly formed aerosols will reflect the incoming solar radiation. Therefore, both the aerosols as the ashes will decrease the amount of solar radiation that reaches the earth's surface, which means that they both have a cooling effect on the earth's climate.
The second chemical shows a completely different life cycle. The hydrochloric acid does have a very short residence time because it easily dissolves in rain droplets. This means that it is easily rained out before it could have had any significant influence on the earth's radiation balance.
The Desert Dust
The desert dust mainly consists of mineral. The desert dust both scatters as absorbs the incoming solar radiation. By absorbing the incoming radiation, the desert dust causes the layer in which the dust resides to heat up. This means that the desert dust potentially causes the climate to warm.
Furthermore, the presence of desert dust suppresses the formation of storm clouds and thereby, it suppresses rainfall. This is why desert dust is expected (ongoing research) to be beneficial for the expansion of the current deserts on earth.
The primary aerosol produced by humans is the sulphate aerosol. This aerosol is produced with the burning of fossil fuels such as oil or coal. That is why this type of aerosol only became important after the industrial revolution, the moment in history, when the usage of fossil fuels started to increase rapidly.
The direct effect of the sulphate aerosols is the reflection of the incoming solar radiation. The main difference with the desert dust is that the sulphate aerosols do not absorb any radiation.
Furthermore, the sulphate aerosols also indirectly affect the radiation balance through their impact on the cloud characteristics. The increased amount of sulphate in the atmosphere leads to a larger number of droplets in a cloud, leading to a higher cloud albedo. Moreover, it is believed that a larger amount of aerosols causes the cloud to exist longer. In both ways, the sulphate aerosol indirectly causes more reflection of the incoming solar radiation.
Based on both the direct as an indirect effect, it can be concluded that the sulphate aerosol has a cooling impact on the climate because it increases the reflection of incoming solar radiation.
Geo-engineering: Injecting Aerosols into the Atmosphere
Geo-engineering is a process in which we as humans try to impact the nature in such a way to prevent climate change.
One way of doing so is by injecting aerosols into the atmosphere. An often named aerosol is the sulphate aerosol. As discussed above, this aerosol is popular because it will result in more reflection of the incoming solar radiation. Meaning that the sulphate aerosol will lead to a cooling of the atmosphere.
Marine cloud brightening
One of the main geo-engineering proposed by scientists is the brightening of the marine clouds. The methods to do so include large ships that emit the aerosols into the atmosphere, as shown in the figure above.
Why specifically in a marine environment?
The reason why researchers focussing on brightening the clouds in a marine environment is because of the deficit of aerosols in a marine environment. This means that adding aerosols in a marine environment has a strong effect on the cloud characteristics such as the cloud albedo.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2021 Tristan
Umesh Chandra Bhatt from Kharghar, Navi Mumbai, India on February 02, 2021:
Very informative. Thanks.
E Randall from United States on February 02, 2021:
Wow, I learned a lot here. It is funny how the smallest things can have the biggest impact.