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Asian Brown Cloud

Last updated date: 24th Feb 2024
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More About Asian Brown Cloud

You must have heard the news of spreading smog in Northern India in the dry winter season whereas also similar news in China when the formation of smog or air pollution can be seen that leads to a reduction in the visibility, affects the transportation system and various diseases as well. This happens because of the special phenomenon that we came to know about in the 1990s and has become a serious issue these days. In this article, we will be talking about this phenomenon which occurs every year and creates various problems including loss of the GDP of the countries on one side and various deaths on the other side. This topic will be helpful for you whenever you are studying the clouds as well as air pollution in Geography or Environmental studies.

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A cloud is an aerosol that is made of water drops and ice crystals floating in the sky. There are many kinds of clouds that can be formed in the atmosphere as per the geographical conditions. Clouds are an important part of the earth's atmosphere which leads to various forms of precipitation especially rainfall. If we talk about a special kind of clouds i.e.. Atmospheric Brown Clouds ( ABCs ), are those clouds that lead to air pollution and consist of aerosols that lead to the absorption as well as scattering the sunlight coming from the Sun. These brown clouds lead to imposing serious impacts not only on the climate but also on human life as well. The first time, this phenomenon was detected in the late 1990s during Indian Ocean Experiment. Let's study comprehensively the phenomena of Asian Brown Clouds below.

About Asian Brown Cloud

It is a form of atmospheric haze that contains particles of black carbon, soot, fly ash, as well as numerous toxic chemicals. These are caused by emissions from the burning of fossil fuels and biomass which is spread across the region. It is a regional size layer of toxic air pollution known as the "Asian Brown Cloud." It appears every year between the months of December and March, the time when there is little to no rain to wash pollutants out of the air. It causes health issues all over the region. All the Asian brown clouds consist of emissions from burning fossil fuels such as coal or petroleum or natural gas products and biomass ( wood, crop stubble). 

This so-called "Asian Brown Cloud" is also known as the " Indian Ocean Brown Cloud."  which is an extensive layer of toxic air pollution. It materializes annually over parts of the northern Indian Ocean, the Indian subcontinent, Bangladesh and China. This term was first used in reports submitted by the UN Indian Ocean Experiment (INDOEX) in 1999. There was research established to measure the atmospheric movements of air pollution from southeast Asia into the Indian Ocean. During this experiment, air pollutants are measured by satellites and surface monitoring stations. They saw a vast carbonaceous aerosol haze over most of South Asia and the northern Indian ocean. While local brown clouds polluted the atmosphere of the urban areas for half a century but the scientists did have any clue about it. And they also do not have any idea about their large scale effects on the temperature of the atmosphere or the issues which are caused by it.

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There are some causes that lead to the occurrence of this atmospheric haze which is mentioned below:

  • All atmospheric brown clouds are made because of the emissions of burning fossil fuels such as coal or petroleum, natural gas and biomass.

  • Due to ABC(Atmospheric Brown Clouds) Sulphur dioxide emissions have increased 600-700 per cent in India and 1000 per cent in China. This happened at the time of 1950.

  • At the same time, soot emissions jumped 300 per cent in India while in China, black carbon emissions rose 500 per cent.

  • Black carbon which is released by incomplete burning of vehicle diesel or fuel is the major constituent of the Asian Brown Cloud and an important contributor to climate change.

  • Nitrogen oxide and Sulphur dioxide emissions from burning coal and other fossil fuels are other important constituents of Asian brown clouds.

  • Air pollution is caused in India by numerous environmentally damaging activities. In Delhi, it is caused by a mixture of coal combustion from coal-fired power plants.

Composition of Atmospheric Brown Clouds

The Asian brown clouds consist of two types of climate pollutants - tiny particles and gases.  The particles are known as "particular matter". In this, several inorganic particles, carbonaceous species, soot, fly ash and mineral dust are included. Among them, black carbon is one of the most significant and damaging components.

Gases that make clouds include SOx(Sulphur oxides), NOx((nitrogen oxides), VOCs (Volatile organic compounds), CO(Carbon monoxide) and CH4 (Methane). These all are the components of ground-level ozone(O3) and other secondary pollutants. The brown colour of clouds are occurring because of the absorption and scattering of sunlight by soil dust particles, black carbon, fly ash and nitrogen oxides.


Asian Brown Clouds cause a greater impact not only on the climate and weather activities of the region but also on Humans as well. Let's have a look at the impacts of these clouds by dividing them into two major categories:

Impacts on Climate

  • Asian Brown Clouds usually consist of black carbon as well as organic carbon which absorbs incoming sunlight and the heat rising from the surface of the Earth and this activity leads to the warmness of the atmosphere and double the heat in the troposphere. This also leads to imposing impacts on the rainfall and water cycle.

  • If we talk about aerosols, the carbon aerosols prevent the sunlight coming from the sun from getting through the surface of the Earth whereas other aerosols lead to send back the sunlight into space. Combinedly, they lead to a phenomenon called dimming. Reduction in the sunlight leads to the cooling effect of the surface of the Earth. 

  • It also affects cloud formation which leads to rainfall. Polluted air is said to have more water-soluble particles than unpolluted air and more particles lead to more droplets which leads to an increase in the albedo or reflectiveness of the clouds. They will reflect more sunlight into the space that will cause more cooling effect here on the Earth but if this cooling effect does not happen then the Indian Ocean will become very hot. Thus, in this case, it represents both positive and negative impacts.

  • The formation of these Asian brown clouds also leads to less rainfall in the region. When the surface temperature reduces because less sunlight reaches the surface and this lower temperature leads to less evaporation which in turn leads to less formation of clouds that will lead to less precipitation. This less rainfall causes great impacts on agriculture and irrigation activities.

  • These clouds lead to impart the regions in various other forms such as in eastern China, a southward shift of summer monsoon occurs and changes in rainfall as well. These clouds also lead to a reduction in summer monsoon clouds in India as well. 

  • On the other hand, it leads to an increase in rainfall in some parts of Australia such as Kimberly and other top-end regions. The emergence of pollutants in India also gets shifted towards the Hindukush mountains which increases the greenhouse effect there.

  • These clouds also cause haze, fog or smog in the Indo Gangetic region in the dry season which leads to air pollution and reduces visibility as well. It also causes impacts on crops and tourists. 

  • Because of these clouds, a various number of cyclones have also been seen in the Arabian sea where the occurrence of this cyclonic activity is very less. Not only this, but these clouds also lead to the melting of ice in the Arctic. According to NASA's GISS, ⅓ of black carbon here comes from South Asia which leads to the melting of ice.

Impact on Humans

  • These clouds can lead to having a great impact on climate and rainfall thus can impact agricultural activities. These impacts can be complex and depend upon the type of crops. For example, according to the studies in 1985-1998, due to air pollution because of these clouds, rice production in India declined by 6.2 million metric tons. According to another study, crop yields can be declined by 20 - 40% in polluted areas.

  • Health effects are also recognised by the United Nations because of these Asian Brown Clouds. PM 2.5 can lead to many diseases such as heart disease, respiratory problems, etc. Ozone can lead to asthma attacks and also reduce lung function. Besides these, cancer-causing agents are also present in these clouds. Around 4,00,000 deaths due to indoor air pollution in India and China whereas 5,00,000 deaths per year due to outdoor air pollution have been seen because of Asian brown clouds. 

  • Besides these, Asian brown clouds can cause economic losses. For example, it causes economic losses of about 2.2% of GDP in India whereas 3.6% of GDP in China. It not only affects the agricultural sector of the economy but also other sectors as well.

Impact of Indian Monsoon on Asian Brown Cloud

Asian brown clouds usually occur from December to March and, after that, these clouds with the arrival of the monsoon washes away. When the monsoon comes, it leads to the presence of rainy months which fulfils the water demand and is helpful for production as well. In these months, it helps in cleansing the air pollution from the atmosphere including the Asian brown clouds. But, because of this activity, some of the pollutants moved to the upper troposphere by the warm air which then spread in the whole world. Actually, all the pollutants are transported above the monsoon clouds into anticyclones from where they are being distributed in the whole world. Besides these, around 10% of Sulphur dioxide emissions also reach up to the stratosphere which leads to an impact on the ozone layer. Therefore, the Indian Monsoon not only helps in removing the air pollution but on the other hand also helps in spreading the air pollution in other parts of the world.

Additional Information

  • The presence of these clouds is not local but regional. For example, the presence of such toxic brown clouds ie. Smog can be seen over Mexico City, Los Angeles for decades. If we talk about ABCs, they not only cover the cities but the whole region. Sometimes the whole continent or ocean might be covered. For example, it can be seen in India, China, Bangladesh, and the Bay of Bengal.

  • The brown clouds do not only occur in Asia but other parts of the world as well such as in North America, South America, Africa and Europe. The main hotspots where ABCs are found are East Asia and South Asia including Eastern China, India, Bangladesh, Pakistan and Southeast Asia which includes Cambodia, Thailand, Vietnam, and Indonesia whereas, in Africa, they can be found in Angola, Zimbabwe and Zambia and also in the Amazon basin in South America.


To conclude, Asian Brown Clouds are a form of smog or haze that is caused by the combination of emissions from power plants, burning of fossil fuels, natural gas products and biomass. It caused health problems all over the region. It is also known as the " Indian Ocean Brown Cloud" which is an extensive layer of toxic air pollution. These kinds of brown clouds not only occur in the Asian regions but also in other parts of the world which affects the climatic and geographical locations over there and also cause various economic and health problems as well. Required steps or measures need to be taken at regional and international levels to control the emissions and air pollution which leads to the occurrence of these brown clouds.

FAQs on Asian Brown Cloud

Question1. What Do You Mean by Asian Brown Cloud?

Answer. It is the form of an atmospheric haze that contains particles of black carbon, soot, fly ash as well as numerous toxic airborne chemicals. It is caused by emissions from the burning of fossil fuels, natural gas products and biomass. It appears for several months every winter in India and China. It is also known as "Indian Ocean Brown Cloud." It is an extensive layer of toxic air pollution.

Question2. What Caused the Brown Cloud Over Asia to Form?

Answer.  The formation of the brown clouds not only occurs in the Asian region but also the other parts of the world. It is the result of emissions from burning fossil fuels like coal and petroleum, natural gas products and biomass (crop stubble, woods). Asian Brown Cloud is caused by the releasing of the black carbon from the incomplete burning of vehicles diesel or fuel. Nitrogen and sulphur dioxide are the other components that are also released from burning fossil fuels. In other regions, it is caused by the burning of coal in power plants.

Question3. How does the Asian Brown Cloud Impact People and the Environment?

Answer. The brown clouds in Asia lead to imposing a great impact on the environment as well on the people. This leads to indoor and outdoor pollution which leads to various deaths in India and China. It affects the cloud formation and thus rainfall patterns as well which affects agricultural activities. The presence of various pollutants leads to many diseases such as heart and respiratory issues and cancer problems, etc. It plays a great role in reducing visibility in the region and also affects the tourists' destinations.

Question4. What is the International Community Doing About the Asian Brown Cloud?

Answer. The United Nations have recognised the major health threats from these brown clouds. The United Nations Environment Program ( UNEP ) also started an international ABS program i.e. for Atmospheric Brown Clouds. For the global climate change mitigation campaign, this international program started identifying the short-lived climate pollutants. The focus is on reducing these SLCPs and this reduction leads to having a great impact on the global climate and global warming.