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Guwahati amongst most polluted cities in the world

The northeastern Indian city Guwahati must have contributed to the Black Carbon (BC) pollutants which is responsible for glacier melting in the Himalayas. Guwahati, the capital city of Assam, adjacent to Bhutan as well as the eastern Himalayas probably accelerated BC concentration to melt glaciers in the region, scientists say. The city is situated on the bank of the Brahmaputra and the BC pollutant emitted from the city effects the Brahmaputra Valley already. The Brahmaputra River Valley (BRV) of Southeast Asia recently has been experiencing extreme regional climate change in the recent years and the carbon emission in Guwahait, the largest city in the valley, is mostly responsible for the changing climate.

A research team from Desert Research Institute, Reno, Nevada, USA with support from NASA calculated that, on an average, this high level of pollutants has given rise to a daily temperature increase of 2 deg Celsius. The research done by Rajan K. Chakrabarty, Mark A. Garro, Eric M. Wilcox and Hans Moosmüller reveals the role of black carbon (BC) aerosols (emitted from vehicles and other combustion sources) in the atmosphere of the region. Strong radiative heating due to wintertime black carbon aerosols in the Brahmaputra River Valley causes health hazards apart from rising temperature. It should be mentioned that further, these pollutants are out-flowing to the Himalayas (where they are melting the glaciers), and interfering with the Monsoon cycle, causing abrupt rainfall and droughts. It should be mentioned that the recent report of the Indian Association of Health Administrators, it says "There has been a rapid increase in Asthma cases in recent years in many parts of India. In Assam, 3% of the population was reported to be suffering from asthma. The reported level of asthma is 3278 per100000 population in Assam, which is higher than the level reported for India as a whole, which is 2468 per 100000 population." Mr Chakravarty ,the Assamese scientist of the research said in this regard that the people of Assam, although unaware of the ill-effects of extreme BC pollution, are still feeling the effects of it. Apart from Asthma, Assam has been experiencing all the symptoms associated with alarming levels of BC pollution since the past 5-6 years -- 1) severe droughts in Assam during 2005-06 and 2008-09 leading to ~$25M in losses due to crop failure; 2) extreme flash flooding during certain years and abnormality in monsoon patterns, and 3) strengthening of pre-monsoon tropical cyclonic systems.

Guwahati has one of the highest Black Carbon pollution levels in the world. The winter-time BC mass concentration observed in the city were higher than those measured in the mega cities of India and China, and much higher than in urban locations of Europe and USA. Mr Chakravarty, who hails from Guwahati, said that it is the rapid urbanization and poor environment quality control in Guwahati which is giving rise to such high BC levels. Guwahati is one of India's most rapidly growing cities since the last 10-12 years. For a rapidly urbanizing city like Guwahati with a million and half population, unfortunately, it doesn't have the infrastructure to sustain this growth. For example, there are just two major roads - GS road and the GNB road - connecting different parts of the city, and very poor public transportation system. The result is people prefer travelling in their private vehicles, which gives rise to severe traffic congestion and increased BC emissions from idling vehicles. With more and more people these days purchasing private vehicles, the energy consumption (fossil fuel) and BC emissions have increased tremendously. According to reports, more than 400,000 vehicles ply on Guwahati's roads every day, and approximately 70% of these vehicles don't have emission clearance certificates. So, we are looking at a situation here where majority of the vehicles plying on Guwahati roads could be emitting excessive amounts of BC and other very toxic pollutants.

The other reason which is affecting Guwahati is unplanned and open burning of solid waste disposal right in the city itself. People don't realize the amount of BC and toxic pollutants which are emitted from burning of waste disposal. In our study, we calculated the BC to increase the daily temperature of Guwahati by 2 degree Celsius -- which is pretty significant. Apart from affecting the climate, these pollutants are carcinogenic and have serious health-effects, he said. According to their research paper published last month in Geophysical Research Letters (VOL. 39, L09804, 5 PP., 2012, doi:10.1029/2012GL051148) Guwahati has one of the highest BC pollution levels in the world which is alarming. A week-long study using a micro-Aethalometer was conducted during January–February 2011 to measure black carbon (BC) aerosol mass concentrations in Guwahati (India), the largest city in the BRV region. Daily median values of BC mass concentration were 9–41 μgm−3, with maxima over 50 μgm−3 during evenings and early mornings. Median BC concentrations were higher than in mega cities of India and China, and significantly higher than in urban locations of Europe and USA. The corresponding mean cloud-free aerosol radiative forcing is −63.4 Wm−2 at the surface and +11.1 Wm−2 at the top of the atmosphere with the difference giving the net atmospheric BC solar absorption, which translates to a lower atmospheric heating rate of ∼2 K/d. To examine the possible outflow trajectories of these aerosols from Guwahati the conducted a 7 day study at different altitude levels from the surface. “The trajectories at all the different heights suggested outflow of pollutants to continental China and Tibet. Such outflow has been suggested to be a major cause of rapid melting of glaciers and permafrost” the researchers write in their reasearch paper.

We asked does the Black Carbon air pollution flow into the Himalayas from Assam and how did you establish this fact and its links with melting of Himalayan glaciers Mr Chakravarty said-“. Yes, the wind blows away the pollution from Assam into the Tibetan region and China. In the Tibetan region, these Black Carbon( BC) pollutants get deposited on the glaciers and/or reside in the atmosphere. Whether deposited on snow or residing in the atmosphere, BC particles absorb incoming sunlight and traps heat in the atmosphere. They act like an invisible blanket in the atmosphere and warms up the atmosphere.” When asked how did they find out that pollution from Guwahati goes to Tibet and China he said that using HYSPLIT computer model of NOAA -- which is a complete system for computing air parcel trajectories to and fro any location in the world. The trajectories at all the different heights suggested outflow of pollutants to continental China and its Tibet region. Such outflow has been suggested to be a major cause of rapid melting of glaciers and permafrost.

Replying to a question Mr Chakravarty said the wind blows away the pollution from Assam into the Tibetan region and China. In the Tibetan region, these Black Carbon( BC) pollutants get deposited on the glaciers and reside in the atmosphere. Whether deposited on snow or residing in the atmosphere, BC particles absorb incoming sunlight and traps heat in the atmosphere. They act like an invisible blanket in the atmosphere and warms up the atmosphere.

Guwahati has one of the highest BC pollution levels in the world which is alarming. People and Govt. of Assam should realize the problems regarding the high pollution levels. Since these pollutants are out-flowing to the Himalayas (where they are melting the glaciers), and interfering with the Monsoon cycle, causing abrupt rainfall and droughts the scientists warned again. If action is not taken immediately, it might be too late for the people of Assam as well as adjacent Bhutan and China.

[The report was based on findings of research works done by a team of scientists from Desert Research Institute, Nevada, USA led by Rajan Chakravarty, the Assistant Research Professor of that institute.
Informations and data provided by the research team show that black carbon (BC) air pollution at different cities in the world are less than Guwahati, whereas BC concentration in the capital city of Assam is around 40 micro gram per cubic m. The BC mass concentration in some cities are 19 -Delhi, 21 -Hydrabad, 6-12 -Kanpur, 26.6 -Kolkata, 7.5- 17.5 -Mumbai, 0.4-10.2 -Banglore, 21.6 -Xi’an China), 3.5-4.2 -Urban areas in Europe and 0.25-3 -Maryland (USA). In Guwahati the BC mass concentration is around 40 microgram per cubic m. It is much higher than any other place on the earth. The table provided by the scientists is attached below. If the truth and reality of Guwahati are denied it will encourage illegal activities pouring toxics to our environment and violation of all pollution control norms rather than taking timely measures.

(Title changed! -- Ed.)

Author info

Chandan Kumar Duarah's picture

The writer is a former Robert Bosch Fellow, an environmentalist and Guwahati based journalist.


Benjamin Kaman's picture

Can anyone assess impact of the two carbon factories in Noonmati, Guwahati? How much share these two factories have?
R. M. Dubey's picture

My attention to the above titled article was drawn by a local T.V. channel based in Guwahati. After going through the article written by Shri Duarah and also the source material published in Geophysical Research Letters (Vol.39, L09804, doi; 10.1029/2012GL051148, 2012, pg1-5) quoted by him in his article, I find the writer of the article had drawn certain conclusions which are contrary to the findings reported in source material quoting conversation with one of the writers of the research paper, Shri Rajan K Chakraborty. In my opinion, the writer of the article, Sri Chandan Duarah, has referred to Guwahati as “most polluted city in the world” by his mere imagination. People in Guwahati in general and authorities concerned to management and control of pollution as well as development in particular are quite upset on the bad publicity given by your news paper about the premier city of NE Region. Though, I do not have data on Comprehensive Environmental Pollution Index (CEPI) concerning to cities worldwide, as per “Comprehensive Environmental Assessment of Industrial clusters”- a report published by CPCB (website in the year 2009 among the 88 industrial clusters spread across length and breath of India, the two clusters from Assam i.e. Burnihat (Guwahati) and Digboi were placed at the bottom of the table showing CEPI scores of 88 clusters under study. CEPI scores included pollution index concerning to air, water and land. A study was sponsored by Planning Commission of India to a leading Environmental Consultancy Firm (PRESTELS) to assess the Environmental Performance of each state in India based on 5 criteria and 16 indicators i.e. Air Pollution, Water Quality, Forest Status, Waste Management, and Climate Change. As per Report circulated by Planning Commission of India, Assam ranks 11th with CEPI score of 6127, among 28 States and 7 Union Territories of India and thus based on these two study reports Guwahati or for that matter Assam can be said to be as one of lesser polluted cities/towns in India, and thus saying Guwahati as most polluted in the world is absurd and ridiculous. The writer of the article, Shri Chandan Duarah, it seems that has not properly understood the findings reported in the source material referred in his article i.e. research paper published by Shri Rajan K Chakraborty of Desert Research Institute, Reno, Navada, USA. At no stage the researchers have concluded Guwahati as the most polluted city based on the study carried out by them for a very limited period i.e. from 27th January 2011 to 2nd February, 2011. Shri Chakraborty et. al. have concluded in the research paper by saying that speculations based on limited observation from one single station i.e. Guwahati are not enough to address adequately the region’s climate change. Nonetheless, the study emphasizes the influence of large Black Carbon emissions on climate of Brahmaputra River Valley Region and the pressing need for future studies. As per observation with regard mean/median Black Carbon (BC mass concentration) values reported in the Journal by Shri Chakraborty, I would like to draw the attention of the researchers about the fact that RSPM and SPM in the air throughout Brahmaputra Valley Region remains very high during the months of December to March because of various geographical reasons connected with the valley. There has been fast industrial as well as infrastructure developmental growth in Guwahati in last 10/15 years but the RPSM and SPM level had seen much higher during the months December and March prior to 1990 too of course, due to various local geographical reasons. Measuring BC mass concentrations in the air during few days of only January and February will not reveal the actual picture for the entire year. Secondly, with regard to comparison of BC mass concentrations of Guwahati with some other cities India as well as, China and the USA, the BC mass concentration data being for different months and different periods cannot be conclusive as admitted by researchers also in Para 7 of their research article. Lastly, I would like to request you to publish this letter in your news paper so that readers who have been misinformed by the contents of the article of Shri Chandan Duarah get the correct picture about the status of pollution in Assam more specially Guwahati. As per data available with PCB Assam I can say it with certainty that the value of SO2 and NO2 in the air of Guwahati remain in the range 4.7 to 7.80 and 12.90 to 16.80 µg/m3 respectively and the RSPM and SPM values range from 39.10 to 93.60 and from 76.00 to 191.70 µg/m3 during the months April to Dec. of 2011, however the respective values of RSPM and SPM for months January to March of 2011 range from 145.2 to 172.00 and 260.80 to 326.00 µg/m3 respectively. This has been the general trend for almost all the years. Lastly, I would conclude by saying that Guwahati may not be one of the cleanest cities in India but it is certainly not the most polluted city in India, what to talk about world. (R. M. Dubey) Chairman PCBA Guwahati
Saptarshi Dutta's picture

Even though there exists a small database pertaining to the level of "black carbon" in the city of Guwahati, it is astounding to see that the city which is not so industrially develped is having a significant concentration of black carbon in the atmosphere. Stern steps must be taken to stop the addition of black carbon in the air. 

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