The cloud color is the effect of scattering and absorption of light in a medium with cloud droplets, and aerosol particles with complicated chemical composition. Quantitatively we are still not able to solve the appropriate scattering equations for such a system. The problem is further complicated by the fact that even in the case of an unpolluted atmosphere we observe clouds with many colors such as white, red, blue, gray and even blue-green. For further discussion please see

http://optics.kulgun.net/Cloud-Colour/

and the entry on atmospheric optics in the Wikipedia

https://en.m.wikipedia.org/wiki/Atmospheric_optics

There is only a very brief mention on the relation of cloud coloring and pollution:

"Yellowish clouds may occur in the late spring through early fall months during forest fire season. The yellow color is due to the presence of pollutants in the smoke. Yellowish clouds caused by the presence of nitrogen dioxide are sometimes seen in urban areas with high air pollution levels. Red, orange and pink clouds occur almost entirely at sunrise and sunset and are the result of the scattering of sunlight by the atmosphere"

-End quote

The problem of investigation of the relation between cloud color and its chemical composition is further compounded by the changing background optical properties of the atmosphere. In the past it was relatively well known that the natural color of sky is blue (as established by Rayleigh, Lorentz, Einstein and Smoluchowki). At the present time, the color of sky is very rarely blue but closer to a milky white. Obviously this change of the background color will affect also our perception of cloud colors.

The complete answer to the question still requires some additional theoretical studies (Mie scattering in a system containing cloud droplets and chemical aerosols) and systematization of the available observations.

Dear Colleague Oueslati,

Atmospheric brown clouds are caused by emissions associated with the combustion of fossil fuels and biomass. The brown colour of the clouds results from the absorption and scattering of solar radiation by black carbon, fly ash, soil dust particles, and nitrogen dioxide. Such sources of air pollution have increased in the past several decades because of rapid economic development. For example, in the second half of the 20th century, black carbon emissions increased by a factor of five in China, and soot emissions rose by a factor of three in India. Sulfur dioxide emissions increased 10-fold in China and 6- to 7-fold in India over the same period.

With my best regards

Prof. Bachir ACHOUR

There is an interesting article on what has been called the "purple haze" cloud in China.

Article A New Type of Haze? The December 2015 Purple (Magenta) Haze ...

Yes, the cloud color is an indicative of Air pollution. The majority of pollutants are: 1. Carbon monoxide 2. Sulfur dioxide 3. Nitrogen dioxide 4. Ozone 5. Particulate matter and 6. Lead

Dear Dr. J.C. Tarafdar,

Thanks a lot for your detailed reply.

With my best regards.

Dr. Adel OUESLATI

Dear Prof. Bachir ACHOUR,

It's a very good reply. Thanks you very much for yur detailed reply which is recommendede by Prof Michael.

With My best wishes!

Dr. Adel OUESLATI

Dear Prof. Michael,

Thanks a lot for your elegant reply. Thanks somuch for the proposed article.

With my best wishes!

Dr. Adel OUESLATI

Again , very little understanding ...

Air pollution is the exposure of the atmosphere to chemicals, particulate matter or biological compounds that cause damage and harm to humans and other living organisms, or cause damage to the natural environment. The atmosphere is a system of reactive and complex natural gases that are necessary to support life on Earth. The depletion of the ozone layer in the stratosphere has long been regarded as one of the most serious threats to human life and ecosystems on Earth.

Air pollution is characterized by a variety of forms of pollution that is rapid spread, where the impact is not limited to the source area, but extends to the neighboring and remote areas, so the air pollution can not be controlled after leaving the source so must be controlled and treated before leaving the atmosphere, It is often not seen by the naked eye as well as multi-source. All these qualities make air pollution a "major environmental issue". Pollution in our country has increased to a very high level, warning of imminent danger, if not controlled as quickly as possible.

Dear Ibtissem,

Thanks somuch for your detailed reply. I agree with you.

with my best regards!

Dr. Adel OUESLATI

Dear Dr. Adel,

I appreciate your questions! Interesting!!

Yes, heavy industrial emissions to atmosphere gives a colour to cloud, depending on the nature of industry. The colour of cloud with pollutants differs from the normal cloud. Prof.Achour and others have mentioned the common pollutants.

Read an article - 'Pollution and clouds'

https://pdfs.semanticscholar.org/ab63/33a770c9a801b33a8c5096fa825d1c798f2f.pdf

Regards

Dear Dr. Asit,

Thanks a lot for your detailed reply. Yes, i agree with you. heavy gas and high-density particles can not move away from the earth because of the gravitational pull. In addition, the density is dependent on the temperature. This may explain the presence of clouds in countries with cold climates and in winter.

Best regards.

Dr. Adel OUESLATI

The cloud color is the effect of scattering and absorption of light in a medium with cloud droplets, and aerosol particles with complicated chemical composition. Quantitatively we are still not able to solve the appropriate scattering equations for such a system. The problem is further complicated by the fact that even in the case of an unpolluted atmosphere we observe clouds with many colors such as white, red, blue, gray and even blue-green. For further discussion please see

http://optics.kulgun.net/Cloud-Colour/

and the entry on atmospheric optics in the Wikipedia

https://en.m.wikipedia.org/wiki/Atmospheric_optics

There is only a very brief mention on the relation of cloud coloring and pollution:

"Yellowish clouds may occur in the late spring through early fall months during forest fire season. The yellow color is due to the presence of pollutants in the smoke. Yellowish clouds caused by the presence of nitrogen dioxide are sometimes seen in urban areas with high air pollution levels. Red, orange and pink clouds occur almost entirely at sunrise and sunset and are the result of the scattering of sunlight by the atmosphere"

-End quote

The problem of investigation of the relation between cloud color and its chemical composition is further compounded by the changing background optical properties of the atmosphere. In the past it was relatively well known that the natural color of sky is blue (as established by Rayleigh, Lorentz, Einstein and Smoluchowki). At the present time, the color of sky is very rarely blue but closer to a milky white. Obviously this change of the background color will affect also our perception of cloud colors.

The complete answer to the question still requires some additional theoretical studies (Mie scattering in a system containing cloud droplets and chemical aerosols) and systematization of the available observations.

Dear Dr. Janusz Pudykiewicz

Thanks a lot for detailed reply.

with my best regards!

Dr. Adel OUESLATI

Dr. Janusz Pudykiewicz,

Very good explanation on the colour of clouds- educative.

I agree with this view - "There is only a very brief mention on the relation of cloud coloring and pollution" - detailed investigations are required to specify the changes of the cloud colours due to different pollutants.

Thanks and regards

Dear Dr. Asit,

Thanks for answer.

Best regards

Adel