(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/<r aAt (18) 

Equation 16 is obtained. 

where 1 is the thickness of the particle layer and crabs is 
A=m/(1-A>)+(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- 
))<i 


where c is the speed of light, m is the average particle 
60 mass, e is the electron charge, and w is the absorption 
line width in sec -1 . 

The greenhouse gases are typically in the earth’s 
stratosphere at an altitude of seven to thirteen kilome¬ 
ters. This suggests that the particle seeding should be 
65 done at an altitude on the order of 10 kilometers. The 
particles may be seeded by dispersal from seeding air¬ 
craft; one exemplary technique may be via the jet fuel as 
suggested by prior work regarding the metallic parti- 



5 , 003,186 


5 

cles. Once the tiny particles have been dispersed into 
the atmosphere, the particles may remain in suspension 
for up to one year. 

It is understood that the above-described embodi¬ 
ment is merely illustrative of the possible specific em- 5 
bodiments which may represent principles of the pres¬ 
ent invention. Other arrangements may readily be de¬ 
vised in accordance with these principles by those 
skilled in the art without departing from the scope and 
spirit of the invention. 10 

What is claimed is: 

1. A method of reducing atmospheric warming due to 
the greenhouse effect resulting from a layer of gases in 
the atmosphere which absorb strongly near infrared 
wavelength radiation, comprising the step of dispersing 15 
tiny particles of a material within the gases’ layer, the 
particle material characterized by wavelength-depend¬ 
ent emissivity or reflectivity, in that said material has 
high emissivities with respect to radiation in the visible 
and far infrared wavelength spectra, and low emissivity 20 
in the near infrared wavelength spectrum, whereby said 
tiny particles provide a means for converting infrared 
heat energy into far infrared radiation which is radiated 
into space. 

2. The method of claim wherein said material com- 25 
prises one or more of the oxides of metals. 

3. The method of claim 1 wherein said material com¬ 
prises aluminum oxide. 

4. The method of claim 1 wherein said material com¬ 
prises thorium oxide. 30 

5. The method of claim 1 wherein said particles are 
dispersed by seeding the stratosphere with a quantity of 
said particles at altitudes in the range of seven to thir¬ 
teen kilometers above the earth’s surface. 

6. The method of claim 1 wherein the size of said 35 
particles is in the range of ten to one hundred microns. 

7. The method of claim wherein said material com¬ 
prises a refractory material. 

8. The method of claim 1 wherein said material is a 

Welsbach material. 40 

9. The method of claim 1 wherein the number of said 
dispersed particles per unit area in the particle layer is 


6 

greater than or equal to \/cr a bsh where 1 is the thick¬ 
ness of the particle layer and cr a bs is the absorption 
coefficient of the particles at the far infrared wave¬ 
lengths. 

10. A method for reducing atmospheric warming due 
to the greenhouse effect resulting from a greenhouse 
gases layer, comprising the following step: 

seeding the greenhouse gases’ layer with a quantity of 
tiny particles of a material characterized by wave¬ 
length-dependent emissivity or reflectivity, in that 
said materials have high emissivities in the visible 
and far infrared wavelength spectra and low emis¬ 
sivity in the near infrared wavelength spectrum, 

whereby said particles are suspended within said 
gases’ layer and provide a means for converting 
radiative energy at near infrared wavelengths into 
radiation at the far infrared wavelengths, permit¬ 
ting some of the converted radiation to escape into 
space. 

11. The method of claim 10 wherein said material 
comprises one or more of the oxides of metals. 

12. The method of claim 10 wherein said material 
comprises aluminum oxide. 

13. The method of claim 10 wherein said material is 
thorium oxide. 

14. The method of claim 10 wherein said seeding is 
performed at altitudes in the range of seven to thirteen 
kilometers above the earth’s surface. 

15. The method of claim 10 wherein said material 
comprises a refractory material. 

16. The method of claim 10 wherein said particle size 
is in range of ten to one hundred microns. 

17. The method of claim 10 wherein said material is a 
Welsbach material. 

18. The method of claim 10 wherein the number of 
said dispersed particles per unit area in the particle layer 
is greater than or equal to \/<r a bs 1, where 1 is the thick¬ 
ness of the particle layer and <r a bs is the absorption 
coefficient of the particles at the far infrared wave¬ 
lengths. 



