Page 1 of 10

European Journal of Applied Sciences – Vol. 10, No. 1

Publication Date: February 25, 2022

DOI:10.14738/aivp.101.11643. Raghuprasad, P. K. (2022). Why the Sky is Blue: The Ozone Connection Revisited. European Journal of Applied Sciences, 10(1). 260-

269.

Services for Science and Education – United Kingdom

Why the Sky is Blue: The Ozone Connection Revisited

Puthalath Koroth Raghuprasad

2400 East 8th Street, Odessa, Texas 79761

ABSTRACT

Blue sky is a feature on earth and Mars, the only planets in our solar system with

well-defined layer(s) of ozone in their atmospheres. After heavy rains remove most

of the dust and varying amounts of gases, the earth’s sky appears deeper blue; this

argues against Rayleigh’s scattering as being responsible for the blue color of sky.

Also, in this paper we make the argument that since at least 50% of earth’s

atmospheric molecules are held close to the surface of the earth, in the lower 6 km

or so, Rayleigh scattering should make the sky closer to the earth appear deeper

blue and the overhead sky lighter; in fact, the reverse is true. We also believe that

scattering of blues in all directions should make the clouds and the objects close to

the ground also to take on the blue color; instead, what we see is white clouds

floating in front of a uniform background of blue and no increase in blue tinge in the

structures close to the earth’s surface. In contrast, the true splitting of setting sun’s

rays makes the light and the sky to take on an orange-red color, but in this setting

the clouds and objects in the rays ’ path also appear yellow-orange, as one would

expect. The absence of blue sky in other planets’ and our moon’s skies despite

having varying mixtures of gases but no defined ozone layer, and the black “sky”

away from the lower parts of the earth’s atmosphere beyond the stratosphere, and

particularly the appearance of a sharp demarcation about the lower part of the

stratosphere where the blue stops and black sky appears, all argue in favor of ozone

as being responsible for the blue color of sky. We propose in this paper that the

proper color of sky is dark blue, as seen in pristine locations and in photographs of

the earth from space, but the sky over cities and other dusty places becomes lighter

blue; the almost white color of sky at horizon is due to the density of dust in the

atmosphere closest to the ground.

Keywords: Blue photons, Ozone, Rayleigh Scattering, Stratosphere, Tropopause,

Troposphere

INTRODUCTION

Rayleigh’s scattering has been the accepted explanation of why the sky appears blue during the

day (1). The theory is that when midday sunlight traverses the troposphere, the air molecules

scatter the shorter wavelength blue photons, while allowing the longer wavelength yellow and

red photons to pass through to the ground. The same phenomenon that imparts blue color to

the daytime sky has been used to explain how the sunrises and sunsets appear orange red. In

a prior paper (2), we explained how instead of the above, the ozone layer in the stratosphere,

might alone explain the blue color of the sky, the layers of dust in the lower troposphere

partially “diluting” the blue of the ozone gas. We proposed that a primary way in which ozone

contributes to the blue color may simply be by its existence in a defined layer, and the

thickness of this layer making the pale blue gas appear deeper blue. Also, we wondered if some

Page 2 of 10

261

Raghuprasad, P. K. (2022). Why the Sky is Blue: The Ozone Connection Revisited. European Journal of Applied Sciences, 10(1). 260-269.

URL: http://dx.doi.org/10.14738/aivp.101.11643

of the short wavelength blue photons are absorbed along with the ultraviolet and displayed by

the ozone layer, which then accentuates the blue of the layer. We speculated that some of the

ozone in the ozone layer might even be deeper blue due to becoming liquefied, in that area of

the stratosphere with the markedly diminished gravity, especially in the sky at the poles. Thus,

both the sky as it appears to observers on the surface of the earth, as well as the appearance of

the earth from outer space, we proposed were due to the ozone. We also observed that the

blue-black to black of the sky over the poles were likely due to the even lower temperatures

prevailing at the poles, especially during winter months making the ozone gas actually

becoming crystallized to blue-black solid. We suspect that it does so, even though the ambient

temperature is not low enough for ozone to liquefy or crystallize on earth, but in the extremely

rarefied state due to reduced gravity, in the tropopause where ozone layer is situated, such

changes in the physical state of ozone may actually take place. This was offered as the true

explanation, rather than a purported “hole” left by loss of ozone due to the use of

chlorofluorocarbons in aerosol cans. We argued that any such depletion of ozone due to the

aerosols would be over the landmasses where people live, especially over the industrialized

countries and not in the poles where there are no human inhabitants. We had also offered some

other phenomena to support the role of ozone in the color of the sky. Such were the presence

of blue sky only on earth and Mars, the only planets with a layer or layers of ozone in their

atmospheres. We also made the argument that after most of the dust and varying amounts of

the atmosphere’s constituent gases were removed by heavy rainfall, the intensification of the

blue color of sky actually supports our notion that the color of the ozone layer is why the sky is

blue.

MATERIALS AND OBSERVATIONS

A search of the NASA’s website (3) and the current scientific literature (4-6) yielded data

pertaining to the types of gases and molecules present in the different layers of the atmosphere

on earth, as well as on those of the other planets in the solar system. Such information is useful

in determining the roles played by the gases in imparting color to the sky. Some of the

discoveries of such searches have been presented in our previous paper (2); the current paper

has included them for the sake of completion, and some are illustrated in figures and tables.

The discovery that not only the sky on Mars is blue, but there are two or more distinct layers of

ozone on its atmosphere, was uniquely useful, as the earth and Mars are the only two planets

with both ozone layer(s) and blue skies. We will describe below in detail those and other

observations that argue in favor of our assessment that ozone alone can explain all the findings

in relation to the color of the sky on earth in various situations and places:

1) The appearance of the sky near the horizon and the color of the clouds and objects

on/near the ground. It is common experience that the sky near the horizon is either

lighter blue or even almost white in most urban locations. This is contrary to what one

would expect, if the blue color of sky is due to blue photons scattering. If such scattering

is due to the gases in the atmosphere, the tighter packed molecules nearer the surface of

the earth should produce deeper blue than the sky overhead. The clouds are white in

color in midday sky (except for the rain clouds). We present two figures below to

illustrate what our normal experience with the color of sky is and that of the clouds and

structures in the scenery, and contrast those with what we expect to see if Rayleigh

scattering is the reason for the blue color of sky.

Page 3 of 10

262

European Journal of Applied Sciences (EJAS) Vol. 10, Issue 1, February-2022

Services for Science and Education – United Kingdom

Fig. 1a Fig. 1b

The figures above are schematic representations of the appearances of the sky, as well as all

structures on the ground as they appear to us (Fig. 1a), and as they would appear if the blue

photons are selectively scattered by the molecules in the air, as is proposed by Rayleigh

scattering theory (Fig. 1b). Notice the deeper blue of sky in the zenith and lighter and lighter

shades as one shifts one’s gaze to the horizon, in Fig.1a. Notice also the clouds are white and

the rest of the scenery are as we usually observe. The image in Figure 1b is the same scenery

but modified to demonstrate how one would expect the same sky, clouds and the objects and

structures would appear if scattering of blues is how the sky attains its blue color. In Fig. 1b,

the sky has deeper hue near the horizon and lighter shades as one approaches the zenith;

likewise, the clouds and all structures close to the ground also have some blue tinge. Of course,

in these highly schematic representations, the different shades of the color of sky are sharply

demarcated. However, in real life the gradations will be gradual; how much of blue is displayed

by clouds, the horizon or the structures on the ground are, of course conjectural. These figures

are just meant to represent and convey the idea.

2)Fifty percent of the total mass of the atmosphere is in the lowest 5.6km of the Troposphere

(3-7). Figure 2 below shows a schematic representation of the strata of earth’s atmosphere on

the left margin, with the percent distribution of the molecules of air in the different parts of the

atmosphere. The latter shows further that 90% of the molecules are held in the lower 16km of

Troposphere. Even in this diagram, which is not to scale, it is obvious that the rest of the earth’s

atmosphere, comprised of the vast majority of space around earth, from Exosphere, through

Thermosphere, Mesosphere and Stratosphere only contain 10% of earth’s atmospheric gases

and molecules.