(Vx United States Patent [19] Chang et al. [ii] Patent Number: 5,003,186 [45] Date of Patent: Mar. 26, 1991 [54] STRATOSPHERIC WELSBACH SEEDING FOR REDUCTION OF GLOBAL WARMING [75] Inventors: David B. Chang, Tustin; I-Fu Shih, Los Alamitos, both of Calif. [73] Assignee: Hughes Aircraft Company, Los Angeles, Calif. [21] Appl. No.: 513,145 [22] Filed: Apr. 23, 1990 [51] Int. a.’ . G21K 1/00 [52] U.S. a. 250/505.1; 250/504 R; 250/503.1; 244/158 R [58] Field of Search . 250/505.1, 504 R, 503.1, 250/493.1; 244/136, 158 R [56] References Cited U.S. PATENT DOCUMENTS 3,222,675 12/1965 Schwartz . 244/158 4,755,673 7/1988 Pollack et al. 250/330 Primary Examiner— Jack I. Berman Attorney, Agent, or Firm —Michael W. Sales; Wanda Denson-Low [57] ABSTRACT A method is described for reducing atmospheric or global wanning resulting from the presence of heat¬ trapping gases in the atmosphere, i.e., from the green¬ house effect. Such gases are relatively transparent to sunshine, but absorb strongly the long-wavelength in¬ frared radiation released by the earth. The method incu¬ des the step of seeding the layer of heat-trapping gases in the atmosphere with particles of materials character¬ ized by wavelength-dependent emissivity. Such materi¬ als include Welsbach materials and the oxides of metals which have high emissivity (and thus low reflectivities) in the visible and 8-12 micron infrared wavelength regions. 18 Claims, 2 Drawing Sheets V/S/8LS 1 5,003,186 2 STRATOSPHERIC WELSBACH SEEDING FOR BRIEF DESCRIPTION OF THE DRAWINGS REDUCTION OF GLOBAL WARMING These and other features and advantages of the pres¬ ent invention will become more apparent from the fol- BACKGROUND OF THE INVENTION This invention relates to a method for the reduction of global wanning resulting from the greenhouse effect, and in particular to a method which involves the seed¬ ing of the earth’s stratosphere with Welsbach-like mate¬ rials. Global wanning has been a great concern of many environmental scientists. Scientists believe that the greenhouse effect is responsible for global warming. Greatly increased amounts of heat-trapping gases have been generated since the Industrial Revolution. These gases, such as CO2, CFC, and methane, accumulate in the atmosphere and allow sunlight to stream in freely but block heat from escaping (greenhouse effect). These gases are relatively transparent to sunshine but absorb strongly the long-wavelength infrared radiation re¬ leased by the earth. Most current approaches to reduce global wanning are to restrict the release of various greenhouse gases, such as CO2. CFC, and methane. These imply the need to establish new regulations and the need to monitor various gases and to enforce the regulations. One proposed solution to the problem of global warming involves the seeding of the atmosphere with metallic particles. One technique proposed to seed the metallic particles was to add the tiny particles to the fuel of jet airliners, so that the particles would be emit¬ ted from the jet engine exhaust while the airliner was at its cruising altitude. While this method would increase the reflection of visible light incident from space, the metallic particles would trap the long wavelength blackbody radiation released from the earth. This could result in net increase in global warming. It is therefore an object of the present invention to provide a method for reduction of global warming due to the greenhouse effect which permits heat to escape through the atmosphere. SUMMARY OF THE INVENTION A method is disclosed for reducing atmospheric warming due to the greenhouse effect resulting from a greenhouse gases layer. The method comprises the step of seeding the greenhouse gas layer with a quantity of tiny particles of materials characterized by wavelength- dependent emissivity or reflectivity, in that said materi¬ als have high emissivities in the visible and far infrared wavelength regions and low emissivity in the near infra¬ red wavelength region. Such materials can include the class of materials known as Welsbach materials. The oxides of metal, e.g., aluminum oxide, are also suitable for the purpose. The greenhouse gases layer typically extends between about seven and thirteen kilometers above the earth’s surface. The seeding of the strato¬ sphere occurs within this layer. The particles suspended in the stratosphere as a result of the seeding provide a mechanism for converting the blackbody radiation emitted by the earth at near infrared wavelengths into radiation in the visible and far infrared wavelength so that this heat energy may be reradiated out into space, thereby reducing the global warming due to the green¬ house effect. 5 lowing detailed description of an exemplary embodi¬ ment thereof, as illustrated in the accompanying draw¬ ings, in which: FIG. 1 illustrates a model for the heat trapping phe¬ nomenon, i.e., the greenhouse effect. 10 FIG. 2 is a graph illustrating the intensity of sunlight incident on earth and of the earth’s blackbody radiation as a function of wavelength. FIG. 3 is a graph illustrating an ideal emissivity ver¬ sus wavelength function for the desired particle mate- 15 rial. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 2 Q FIG. 1 shows a model for the heat-trapping (green¬ house effect) phenomenon. It is assumed that the green¬ house gases are concentrated at altitudes between y=0 (at some altitude Yj, above the earth’s surface) and y= 1. Regardless of the sunshine reflected back into 2j space, i| and i2 denote the shortwavelength sunlight energies that are absorbed by the earth’s surface and the greenhouse gases, respectively. Available data shows that ii=0.45 i w i and i2=0.25 i so i, where i J0 / is the total flux from the sun. The short wavelength sunlight heats 30 up the greenhouse gases and the earth surface, and this energy is eventually reradiated out in the long wave¬ length infrared region. FIG. 2 is a graph illustrating the intensity of sunlight and the earth’s blackbody radiation as a function of 35 wavelength. As illustrated, some 30% of the sunlight energy is in the near infrared region. The earth’s black¬ body radiation, on the other hand, is at the far infrared wavelength. Referring again to FIG. 1, I„ I+, I_, I g and \ e repre- 40 sent the fluxes in the infrared wavelength region, where Is and l g are the fluxes reradiated by the greenhouse gases toward the sky and ground, respectively; I<. is the flux reradiated by the earth; and 1+ and I_ are fluxes within the gases radiating toward the space and ground, 45 respectively. 1+ and I_ are functions of y, e.g., I + (0) is the 1+ flux at y=0. Considering the principles of en¬ ergy conservation and continuity at boundaries, the following relationships are obtained: 50 I;=h+il (1) W+OXl-R/) (2) /_(!)=/+(!)«, (3) / + (0)=/_(0)R o +/ t (I-K„) 60 ig=i-m\-Ro)+i'Ro 65 I e =/BB(T e )(l-R)+/ l! R (6) I'=h+/g (7) 5 , 003,186 where Ro, R/and R are the reflectivities at the y=0 and y = 1 boundaries and at the earth’s surface. I&g(T<.) is the blackbody radiation flux at the earth’s temperature T e . Within the greenhouse gases’ layer, the energy equa- where Ifij(T g ) is the blackbody radiation flux at the greenhouse gases’ temperature T g , and a is the absorp¬ tion coefficient of the gases. The solutions of equations 8 and 9 are given by equations 10 and 11: To illustrate the effects of R 0 and R/ on the green¬ house effect, the extreme case is considered wherein a high concentration of greenhouse gases has strong ab¬ sorption in the infrared region; that is, for y = 1 , e~ al approaches 0. Then, using Equations 3 and 4, the rela¬ tionships of Equations 12 and 13 are obtained. From Equations 5 and 7, From Equations 2 and 1, To achieve a lower temperature of the earth, (consid¬ ering ij, i2 and R as constants), it is desirable to make R and R/ as small as possible. Known refractory materials have a thermal emissiv- ity function which is strongly wavelength dependent. For example, the materials may have high emissivity (and absorption) at the far infrared wavelengths, high emissivity in the visible wavelength range, and very low emissivity at intermediate wavelengths. If a mate¬ rial having those emissivity characteristics and a black body are exposed to IR energy of equal intensity, the selective thermal radiator will emit visible radiation with higher efficiency (if radiation cooling predomi¬ nates), i.e., the selective thermal radiator will appear brighter than the black body. This effect is known as the Welsbach effect and is extensively used in commercial gas lantern mantles. Welsbach materials have the characteristic of wave¬ length-dependent emissivity (or reflectivity). For exam¬ ple, thorium oxide (TI1O2) has high emissivities in the visible and far IR regions but it has low emissivity in the near IR region. So, in accordance with the invention, the layer of greenhouse gases is seeded with Welsbach or Welsbach-like materials which have high emissivities (and thus low reflectivities) in the visible and 8-12 mi¬ crometer infrared regions, which has the effect of re¬ ducing R 0 and R/ while introducing no effect in the visible range. A desired material for the stratospheric seeding has a reflection coefficient close to unity for near IR radia¬ tion, and a reflection coefficient close to zero (or emis- sity close to unity) for far IR radiation. FIG. 3 is a graph illustrating an ideal emissivity versus wavelength func¬ tion for the desired material. Another class of materials having the desired property includes the oxides of met¬ als. For example, aluminum oxide (AI2O3) is one metal oxide suitable for the purpose and which is relatively inexpensive. It is presently believed that particle sizes in the ten to one hundred micron range would be suitable for the seeding purposes. Larger particles would tend to settle to the earth more quickly. The particles in the required size range can be ob¬ tained with conventional methods of grinding and meshing. It is believed that the number of particles nj per unit area in the particle layer should be defined by Equation Combining Equations 14 and 15, the relationship of 50 n rf i § i/)+(m+'2 )/0—*/) (16) the absorption coefficient of the particles at the long IR wavelengths. One crude estimate of the density of parti- Finally, Equation 6 gives the blackbody radiation 55 cles is given by Equation (19): from the earth’s surface in terms of ii and i2 and the three reflectivities: n rf ig(cmw)/(4jre 2 ) (19) lBBHT')=i\/(\-Ro)+(i I +i 2 )/(\-Ri)+(R/n-R- ))