Ⅰ. The Concept of Artificial Injection of Aerosol
The technology of injecting aerosols into atmosphere artificially uses Geoengineering methods. To explain artificial injection of aerosol, therefore, we need to know the concept of Geoengineering first. The Royal Society of London for Improving Natural Knowledge, which is the society for natural sciences founded in the UK, defines Geoengineering as “large-scale intervention in the climate system by deliberately modifying the Earth’s energy balance to reduce increases of temperature and eventually stabilise temperature at a lower level.” That is, Geoengineering changes the overall climate system by using artificial methods to solve problems of global warming. It can be classified into two engineering methods :
① CDR, Carbon Dioxide Removal
(removal technology of carbon dioxide from the atmosphere)
② SRM, Solar Radiation on Management
(technology of reflecting some part of sun light and heat to the space)
Among them, we will focus more on the second method, SRM. SRM technology controls the climate system by reflecting the solar light artificially and is also called as “Solar Engineering”. The artificial injection of aerosols into the atmosphere that we want to analyze comes under SRM. Frequently used aerosols are sulfate particles, calcium carbonate particles, sea-salt aerosols, sulfurous acid aerosols(H2S, SO2), and aluminum oxides. Then, how do we inject aerosols into the atmosphere? Two technologies of injecting aerosols into the atmosphere are listed below.
① CDR, Carbon Dioxide Removal
(removal technology of carbon dioxide from the atmosphere)
② SRM, Solar Radiation on Management
(technology of reflecting some part of sun light and heat to the space)
Among them, we will focus more on the second method, SRM. SRM technology controls the climate system by reflecting the solar light artificially and is also called as “Solar Engineering”. The artificial injection of aerosols into the atmosphere that we want to analyze comes under SRM. Frequently used aerosols are sulfate particles, calcium carbonate particles, sea-salt aerosols, sulfurous acid aerosols(H2S, SO2), and aluminum oxides. Then, how do we inject aerosols into the atmosphere? Two technologies of injecting aerosols into the atmosphere are listed below.
Ⅱ. Two Technologies of Injecting Aerosols into The Atmosphere Deliberately
① SAI (Stratospheric Aerosol Injection)
The technology motivated by a global cooling effect of Mount Pinatubo’s explosion (explained at the front of the web page) is SAI. It is the engineering method to lower the temperature of the earth by using the principle that aerosols emitted into the stratosphere block incidence of solar light and make the amount of sunlight reaching the surface of the earth reduced. Here comes a question. Why are aerosols sprayed into ‘the stratosphere’ among the Earth's atmosphere? In terms of accessibility, the troposphere is rather the most efficient. Because the stratosphere is an inversion layer, vertical movement is suppressed, and convection rarely occurs. Eventually, the residence time of matter in the stratosphere becomes relatively longer than in other atmospheres. Therefore, spraying into the troposphere causes aerosols to rain and descend to the ground within a few weeks, but if aerosols is sprayed in the stratosphere, they remain in the air for a year or two.
To inject aerosols, SAI uses tools such as large air balloon, airplane, long hose, and gun. It distributes aerosols in several places rather than focusing on one. Examples of studies using SAI include the SCoPEx project, the SPICE project (Strategic Particle Injection for Climate Engineering), and so on. Below is a description of the research process and the ongoing experiments of the SCoPEx project.
The technology motivated by a global cooling effect of Mount Pinatubo’s explosion (explained at the front of the web page) is SAI. It is the engineering method to lower the temperature of the earth by using the principle that aerosols emitted into the stratosphere block incidence of solar light and make the amount of sunlight reaching the surface of the earth reduced. Here comes a question. Why are aerosols sprayed into ‘the stratosphere’ among the Earth's atmosphere? In terms of accessibility, the troposphere is rather the most efficient. Because the stratosphere is an inversion layer, vertical movement is suppressed, and convection rarely occurs. Eventually, the residence time of matter in the stratosphere becomes relatively longer than in other atmospheres. Therefore, spraying into the troposphere causes aerosols to rain and descend to the ground within a few weeks, but if aerosols is sprayed in the stratosphere, they remain in the air for a year or two.
To inject aerosols, SAI uses tools such as large air balloon, airplane, long hose, and gun. It distributes aerosols in several places rather than focusing on one. Examples of studies using SAI include the SCoPEx project, the SPICE project (Strategic Particle Injection for Climate Engineering), and so on. Below is a description of the research process and the ongoing experiments of the SCoPEx project.
AN EXAMPLE |
DETAILS Researchers including climate scientist David Keith at Harvard University studied for the first time to find the right level of solar engineering to slow down climate change without side effects. A thesis published in 2014 suggested that controlling the rate of temperature rise by half by SAI could reduce the change in precipitation and offset the intensity of hurricanes by more than 85 percent. Since 2018, flight tests have been carried out gradually. In 2021, large air balloon loaded 600kg of calcium carbonate particles and experimental equipment equipped with propellers and sensors will be carried up to 20km above the ground. Then, it sprays calcium carbonate particles from 100g to up to 2kg to form a reflective particle layer of 1km long and 100m wide. By measuring the rate of light reflectivity, this experiment will evaluate the decrement in sunlight entering the Earth and the rate of temperature change. |
② Creating artificial cloud by sea-salt aerosols
The technology of artificial cloud-forming using sea-salt aerosols was motivated by the fact that the particles released from the ship affect the cloud on the ocean because sea-salt aerosols play a role of cloud condensation nucleus(CCN). To explain briefly, it is the engineering method using the principle of using special ships to lift sea water (sea-salt aerosols acting as CCN up to powerful turbines) and spray it into the atmosphere to create cloud or fog artificially. Created artificial cloud makes the albedo(reflectivity to sunlight) increased and cloud last longer. That is, it can reflect more sun light. This method works better with the more sprayers installed on the ship and the lower the albedo of the original ocean. Below is a description of the research using the technology of creating artificial cloud by sea salt particles.
The technology of artificial cloud-forming using sea-salt aerosols was motivated by the fact that the particles released from the ship affect the cloud on the ocean because sea-salt aerosols play a role of cloud condensation nucleus(CCN). To explain briefly, it is the engineering method using the principle of using special ships to lift sea water (sea-salt aerosols acting as CCN up to powerful turbines) and spray it into the atmosphere to create cloud or fog artificially. Created artificial cloud makes the albedo(reflectivity to sunlight) increased and cloud last longer. That is, it can reflect more sun light. This method works better with the more sprayers installed on the ship and the lower the albedo of the original ocean. Below is a description of the research using the technology of creating artificial cloud by sea salt particles.
AN EXAMPLE |
DETAILSStephen Salter, the Professor of the University of Edinburgh, planned with Dr. John Radem, a British atmospheric scientist at the American Federation of Meteorological Research, to implement the method using sea salt particles. Now, his team has designed a ship that uses computers and wind power to remotely operate cylindrical cylinders. The electricity obtained by rotating the cylinder is used to turn the motor that pulls up sea water. Professor Stephen Salter said, "With technology that can spray 10,000 liters per second, we can reverse the global warming damage so far." According to the study, designed ships can spray 50,000 liters of water every second and reduce global temperature to 1.5 degrees Celsius with 300 automatic ships. In addition, creating artificial white clouds to lower the water temperature can cope with hurricanes and El Nino, which get stronger as the ocean water temperature rises. |
Ⅲ. Problem Posing
Above, we explore the concept of artificial injection of aerosols into atmosphere that is a method included in SRM, two technologies for it, and related examples. However, as you can infer from the above two examples, these technologies are still in the research and development stages. That is, it is hard to apply SRM on a large scale in real atmosphere because unforeseen accidents or dangerous side effects may occur and numerical models to assess the effectiveness of climate engineering technologies have not yet been perfectly constructed.
Therefore, it is necessary to analyze the factors affecting the effectiveness of Geoengineering technologies. One of the many factors is ‘the type of aerosol injected into the atmosphere’. Focusing on the SAI among the two technologies described above, we would like to analyze which aerosol material is most suitable for this technique to achieve maximum efficiency.
According to one study, if the size of the particle released into the atmosphere after volcanic eruption is smaller than the sulfuric acid aerosol(having an effective radius of around 0.4 μm), the effectiveness of blocking increases. Therefore, sulfate or nitrate aerosols, which have smaller size than sulfuric acid aerosols, are widely used in several SAI studies. Based on this information, we assumed that sulfate aerosols, which can be called pollution aerosols, would be the most effective aerosols. On the next page, we will demonstrate this through an in-depth analysis using logical grounds.
To explain the process briefly, we classified aerosols into dust aerosols, sea-salt aerosols, pollution aerosols in the previous step. First, using AOD and FF, we will analyze which of the three types of aerosols is most efficient. Then, Among the most efficient specific aerosols analyzed above, we will determine which component of aerosol can effectively maximize the amount that reflects sunlight by using the inherent property of the material.
Therefore, it is necessary to analyze the factors affecting the effectiveness of Geoengineering technologies. One of the many factors is ‘the type of aerosol injected into the atmosphere’. Focusing on the SAI among the two technologies described above, we would like to analyze which aerosol material is most suitable for this technique to achieve maximum efficiency.
According to one study, if the size of the particle released into the atmosphere after volcanic eruption is smaller than the sulfuric acid aerosol(having an effective radius of around 0.4 μm), the effectiveness of blocking increases. Therefore, sulfate or nitrate aerosols, which have smaller size than sulfuric acid aerosols, are widely used in several SAI studies. Based on this information, we assumed that sulfate aerosols, which can be called pollution aerosols, would be the most effective aerosols. On the next page, we will demonstrate this through an in-depth analysis using logical grounds.
To explain the process briefly, we classified aerosols into dust aerosols, sea-salt aerosols, pollution aerosols in the previous step. First, using AOD and FF, we will analyze which of the three types of aerosols is most efficient. Then, Among the most efficient specific aerosols analyzed above, we will determine which component of aerosol can effectively maximize the amount that reflects sunlight by using the inherent property of the material.