In terms of sulfate aerosols, which are created by sulfur dioxide given off by power plants, the US and Europe have very successfully used sulfur dioxide scrubbers in power plants to reduce these emissions over the past 20 years or so. But we can definitely do more. By reducing aerosol soot emissions, we can buy ourselves some climate time — about 5 to 10 years — while we work on reducing emissions of greenhouse gases such as carbon dioxide CO2 in parallel.
CO2, you see, hangs around in the atmosphere for an extremely long time, from decades to centuries, so even if we implement cuts today, it will take years for them to take effect. Aerosols, on the other hand, have much shorter lifetimes.
If we work to reduce soot emissions now, which can enhance the global warming effect of CO2 by percent, the climate impacts will be felt more rapidly. I have a paper in review at the moment that is quite exciting; we're looking at the future total climate impacts of current emissions from different industries, taking into account the effects of both greenhouse gases such as CO2, ozone and methane, and the impacts of aerosols.
What we've found is that for the next 40 years, emissions from road vehicles will have the largest global warming impacts of all human activities — because of the air pollutant effects that enhance greenhouse gas warming.
After , however, power sector emissions are by far the largest global warmer because of the build up of CO2 in the atmosphere from that activity. There are a few other relevant questions coming out of this. However, the last five to ten decades have witnessed the obvious warming of Earth Shove, Intergovernmental Panel on Climate Change IPCC found that the warming of the climate system was undoubtedly and observed changes have never occurred for decades or even thousands of years since the s.
Global warming has been extremely apparent and the average global temperature has been increasing since the Industrial Revolution. The year from to saw a gradual increase in the mean temperature, and the average temperature rose for around 0. Global warming is a continuous process and the mean temperature is predicted to rise another 0.
Human activities, especially the burning of fossil fuels, are related to the generation of greenhouse gases which mainly contain carbon dioxide Santer et al. In the early twenty century, few studies suggested that temperatures in polar religions had been rising, but these changes have not been formally put down to human activities because of the scarcity of observations and spontaneous change Polyakov et al.
However, through analyzing the data for the temperatures of the land surface Gillett et al. Carbon dioxide, water vapor, and methane are major greenhouse gases that block the energy from the sun reflecting out to space. Atmospheric photochemistry focus on the interaction between greenhouse gases and incident solar radiation. Greenhouse gases absorb solar radiation. Figure 1. The change of global mean temperature from to Anthropogenic emissions also generate aerosols.
As opposed to the greenhouse gases, the effect of aerosols is to cool the atmosphere. The aerosol optical depth gives information about how much direct sunlight is blocked by aerosols and fails to reach the ground. Photochemical smog or ground-level ozone, has been the most severe air pollution problem, thus, by reducing sulfur and hydrocarbon emissions Dickerson et al.
Atmospheric aerosols are suspensions of submicroscopic and microscopic particles which originate from a variety of natural and anthropogenic sources. The most obvious example of an aerosol in the atmosphere are clouds, which is mainly composed of concentrated water with a particle diameter of about 0. However, in atmospheric science, the term aerosol has traditionally referred to suspended particles containing a large amount of condensed matter other than water.
Atmospheric aerosols play an important role in climate and atmospheric chemistry. Aerosols affect the climate because they affect the radiation balance of the planet.
Both direct and indirect aerosol effects act toward reducing Sea Surface Roughness SSR with increasing aerosol levels.
The magnitude of these effects depends on the composition of the individual particles and how they are assembled in the population. The effects of greenhouse gases and aerosols are opposite to the climate system. Combined with the increasing concentration of greenhouse gases in recent years, the greenhouse effect is going to have more impacts not only global warming.
Aerosols affect the climate in two primary ways: by changing the amount of heat entering or leaving the atmosphere, or by affecting how clouds are formed. The effect of atmospheric aerosols is more complicated than greenhouse gases Mitchell et al.
Generally, bright or translucent particles tend to reflect radiation in all directions and return to space, while dark aerosols could absorb a large amount of light Watson et al. Most aerosols are brighter than land or ocean, cooling the earth by reflecting sunlight into space like pure sulfates and nitrates reflect almost all the radiation they encounter, cooling the atmosphere.
However, there are some aerosols absorb sunlight such as black carbon which absorbs radiation and warms the atmosphere. If the aerosol forcing has a small uncertainty range, the aerosol can only offset a small part of the greenhouse effect. If we assume that aerosols offset most of the greenhouse effect, a possibility that is entirely consistent with current uncertainty. Then the temperature would increase around 0.
If temperature sensitivity is high, global warming may accelerate sharply in the future. Whether in cities or remote areas, the atmosphere contains a large number of aerosol particles.
A complete description of the aerosol size distribution may also include calculations for each particle size. Because the position of aerosols varies with time and space, it is difficult to calculate particle size. Besides, changes in atmospheric aerosol concentrations over short time scales are also often quite significant. The size distribution of a particle swarm can also be described by its cumulative distribution Torres et al.
The cumulative distribution value of the particle size segment is defined as the particle concentration that is less than or equal to the particle size range. As for the chemical composition, atmospheric aerosol particles contain sulfates, nitrates, ammonium, organic matter, crustal matter, sea salt, metal oxides, hydrogen ions, and water.
Different experts describe particles based on their shape, size, and chemical composition. Toxicologists call aerosols superfine, fine, or coarse. Fine particles that are less than 2.
Coarse particles are relatively large particles—greater than 2. Submicron aerosols are dominated by organic components and nitrates, as well as sulfate, ammonium, and black carbon. The contribution of carbon, nitrogen, and sulfur to the composition illustrates the role of aerosols in the biogeochemical cycle.
Compounds that exist as organic aerosols in the atmosphere are a mixture of aerosols and gaseous organics. It is difficult to accurately model them due to the complexity of their sources, composition, and atmospheric aging mechanisms. Organic aerosols are generally divided into primary organic aerosols and secondary organic aerosols Crippa et al. Due to the different formation, primary aerosols contain particles introduced directly into the gas and secondary aerosols form through gas-to-particle conversion.
Secondary organic aerosols are formed by the oxidation of volatile organic compounds in the troposphere, and their low vapor pressure oxidation products are distributed between the gas and the aerosol phase. Primary organic aerosols are atmospheric particles that are emitted or injected directly into the atmosphere.
These are many kinds of atmospheric primary aerosols Hodzic et al. Sand dust aerosols have not only natural sources, but also man-made sources, including urban fugitive dust, which is made of mineral aerosols generated by industrial activities such as incompletely burnt coal dust, road excavation, uncovered, construction sites and cement, and artificial dust produced by human activities such as agricultural activities Gillett et al.
The absorption characteristics Ginoux et al. Sand dust aerosols will not only change the regional atmospheric radiation characteristics but also have a great impact on the regional water cycle, monsoon system, and local climate environment Zhang et al. Comparing the distribution of sand and dust in different seasons, the distribution of sand and dust has obvious seasonal differences. From the global regional average, spring is the largest, summer is the second, then autumn and winter are the smallest.
Aerosol optical thickness AOD , single-scatter albedo SSA , asymmetry factor ASY , and volume spectral distribution are the key parameters to estimate its radiative forcing. At present, there is still a lot of uncertainty in the assessment of the climate and environmental impacts of sand and dust aerosols.
The main reason is the lack of understanding of the sand and dust source area Zhang et al. Besides, there is a lack of system information on the physical, chemical, and optical properties of sand and dust aerosols. The photooxidation of isoprene results in the formation of secondary organic aerosols. A series of controlled experiments Surratt et al. However, the characters of oligomers depend largely on the level of nitrogen oxides, and acidic products are formed only under conditions of high nitrogen oxides.
Secondary organic aerosols are formed in the air through physical and chemical processes such as oxidation and then nucleate or condense. Volatile and semi-volatile organic compounds in the atmosphere are oxidized in the atmosphere to form secondary organic aerosols, which are concentrated and enter the atmospheric aerosols and become their constituents. Most secondary organic aerosols exist in the troposphere Torres et al.
Besides, they have a serious impact on climate change and air pollution. When observing the motion of aerosols in a fluid, we need to start from the perspective of the transport process. For the microscopic scale, a fluid molecule collides with another molecule after moving in a straight line. The molecule changes direction after the collision and collides with another molecule after moving for a while Jennings, We can distinguish two cases based on the relative size of the particles suspended in the gas and the average free path of the surrounding gas molecules Signorell et al.
If the diameter of the particles is much bigger than the mean free path of the surrounding gas molecules, the gas is considered a continuous fluid, thus, the mean free path could be expressed by the above formula. In this case, the velocity of target molecules should not be ignored and the frequency of the collision depends on the average velocity of the randomly moving molecules.
As long as the aerosol particles do not move in a vacuum which is not ideal, resistance will always exist. To calculate the resistance of a fluid to a particle moving in the fluid, you need to solve the fluid motion equation Arnold, to determine the velocity and pressure fields around the particle. And the Navier-Stokes equation, where the x component is where g x is the component of gravity in the x-direction :. By introducing characteristic velocity Uo and length L, the continuity equation and Navier-Stokes equation can be made dimensionless.
For the flow around the submerged body, L can be selected as the characteristic size of the body, such as diameter, and u 0 can be selected as the velocity of the undisturbed fluid upstream of the body.
When the particle size is small and the flow velocity is low, the Reynolds number is small and the flow is laminar Sehmel, In this case, the inertial force is negligible compared to the viscous force. Then we can get the drag coefficient in the laminar flow regime. Inversely proportional to the drag coefficient Re p :.
The movement of aerosol particles is first caused by certain external forces, such as gravity or electricity Alonso, When the speed of the particles differs from the speed of the fluid, resistance is created. The acceleration experienced by a particle is proportional to the sum of the forces acting on the particle.
The combined force exerted by the fluid on the sphere in the direction of flow is composed of two parts. At each point on the surface of the sphere, there is a pressure on the solid perpendicular to the surface of the sphere. This is a normal force. At each point, the fluid also exerts a tangential force due to the shear stress caused by the velocity gradient near the surface. A sphere moving at velocity u in a fluid is perfectly equivalent to a sphere moving at velocity u in a stationary fluid.
The total resistance of the fluid to the sphere is:. If we include gravity, the total force acting on the sphere is the sum of drag and buoyancy. When the direction of flow coincides with the direction of gravity, the buoyancy added to the resistance is equal to the weight of the fluid discharged by the sphere.
To consider the resistance in the entire Reynolds number range, we can express the resistance with the empirical resistance coefficient C D A p is the projected area of the body normal to the flow. Brownian motion of a small particle in a stationary fluid is controlled by the following Langevin equation in the x-direction.
Because of the noncontinuous forces on the suspended fluid molecules, the suspended fluid molecules cause irregular and sharp movements to the particles and the random acceleration n t is discontinuous. To study Brownian motion, the behavior of the entire particle swarm or particle ensemble must first be considered. If a large number of particles are released from the origin and all their y displacements at time t are averaged, the expected overall average displacements should be zero Davies, This is because there is no constant n t inherent in a specific direction.
The mean square displacement of the Brownian motion can be expressed as:. Brownian motion is a continuous random process and its essence is the random motion of brown particles under the random impact of molecules. It is impossible that aerosol particles move in a vacuum environment, thus, we need to consider the external resistance to know the motion of the particles. The mean free path is a good reference variable.
Deliquescence and weathering are the two most important phase transition processes for studying the hygroscopicity of aerosol particles. During the water absorption process, due to the irregular shape of the aerosol particles and the diversity of the internal structure, water vapor in the environment adheres to the aerosol particles through physical adsorption, chemical absorption, and capillary adsorption.
This relative humidity is called the deliquescent point, which is the saturation concentration point of the droplets. When the relative humidity continues to increase, the droplets can continue to absorb water, which causes the concentration in the droplets to decrease and the volume to increase.
For chemical components that are insoluble in water, a liquid-water-encapsulated core structure may be formed Zhang et al. In the process of dehydration, aerosol droplets often do not crystallize into a solid at the deliquescent point. When the ambient relative humidity drops below the deliquescent point, the droplets tend to form metastable supersaturated aerosol droplets.
When the relative humidity continues to drop, the droplet concentration gradually reaches the critical concentration of the supersaturated aerosol, and the water content begins to evaporate with solid aerosol particles forming. As an organic part of the atmospheric hydrosphere cycle, atmospheric aerosols mainly affects the microphysical processes of clouds and precipitation, and also affects atmospheric stability and cloud albedo.
It not only increases or decreases the amount of rainfall, but also changes the type of cloud and rain such as converting non-precipitating clouds into precipitation clouds. The indirect effects of atmospheric aerosols are closely related to changes in the water cycle in the climate system. If the liquid water content does not change, the effect of aerosols on cloud droplet concentration or size caused by microphysical processes is called the first type of indirect effect.
Due to the introduction of more aerosol particles as condensed nodules, under a certain water content, cloud droplets compete with each other for water vapor, and they cannot grow up to the precipitation mass point Ramanathan et al. Thus, there are more small cloud droplets in the cloud, which results in a decrease in precipitation.
Also, due to the enhanced albedo of small cloud droplets Rosenfeld et al. From the above, we know that once aerosol particles enter the cloud, they could change the precipitation properties and radiation characteristics of the cloud, thereby affecting the precipitation and water cycle. The energy balance of the earth-atmosphere system is the driving force that determines the climate state of the earth.
The short-wave solar radiation received at the top of the atmosphere by the ground-gas system must be equal to the long-wave or infrared radiation emitted by the ground-gas system itself Murthy, For whatever reason, if this balance is disturbed or disrupted, it will cause climate change. In other words, this disturbance either reduce or increase the received solar radiation and the emitted long-wave radiation from the earth, which could lead to the energy budget of the earth-gas system deviates from its equilibrium state.
For example, the greenhouse effect caused by the increasing concentration of greenhouse gases reduces the long-wave radiation emitted or lost by the earth-gas system. Aerosols have a cooling effect on the ground, partially offsetting global warming caused by greenhouse gases.
While, due to their physical properties, different types of aerosol particles have different absorption and scattering effects, so that the radiative forcing in the atmosphere is different. Atmospheric aerosol particles have two climate effects. Secondly, used as condensed nodules in clouds to change cloud microphysical processes and precipitation properties, aerosols could change the water cycle of the atmosphere which also have important impacts on many aspects of economic society Mitchell et al.
For climate change in the past centuries, the general trend is warming, which is mainly caused by human activities and natural changes. The cooling effect of anthropogenic sulfate aerosols in the tropospheric atmosphere on the ground surface could offset some of the warming effects Solomon et al. However, the spatial-temporal heterogeneity of aerosol distribution on the global scale and the differences in the radiation characteristics of different components have led to great differences in estimates of direct radiative forcing effects Rood et al.
Therefore, a clean atmosphere in the future can cause global temperatures to increase faster and higher, leading to a more severe global warming situation. Black carbon aerosols are ranked second to carbon dioxide in contributing to the greenhouse effect.
Aerosols are known to increase radiation in the longer wavelengths longwave and decrease radiation in the shorter wavelengths shortwave. The strength of these effects depends on the size and chemical nature of the aerosol particles. Using the framework to analyze a massive dataset developed by NASA, Chakraborty found that although the longwave effect of aerosols has generally been considered by the scientific community to be less important, the climate is more sensitive to it than to the shortwave effect.
This is because of the absence of the shortwave effect at night, a time when the atmosphere is more stable -- and thus more sensitive to radiation. It is also the result of the high climate sensitivity in arid regions, where the longwave effect is prevalent due to the presence of aerosols from coarse mineral dust. Combined, the longwave and shortwave effects reduce the terrestrial diurnal temperature range by almost one degree Fahrenheit.
Aggregating the eight major regions of interest used in the study, about half of this reduction is due to human-made aerosols. There are also long-term trends, Chakraborty said, that show an intensification of the local climate sensitivity in the tropics due to deforestation between and , demonstrating the importance of vegetation in regulating interactions between aerosols and the climate. Original written by Josh Anusewicz. Note: Content may be edited for style and length.
Science News. Journal Reference : T.
0コメント