India's wealth of flora and fauna provide a rainbow of natural dyes
Searching for Roots
The lac dye is bright red. It is derived from insects like cochineal, kermes and lac, also called Kerria lacca. It takes about three lakh insects to yield one kilogramme of dye.
These scale insects thrive on a variety of trees and bushes such as kusum (Schleichera oleosa), palash (Butea monosperma), ber (Ziziphus mauritiana). They can be destructive to trees, stunting or killing twigs and branches by draining the sap. They exude a secretion from their bodies, which forms a hard resinous layer. This is the lac resin or sticklac.
Before they damage the trees, the insect bodies along with its secretions are scraped off from the twigs and branches and manufactured into shellac that yields the lac dye. Natural colouring substances, derived from shellac, like carminic acid, kermesic acid and laccaic acid are popularly known as the lac dye.
India is endowed with a wealth of natural flora and fauna, which provide the basic resource for a rainbow of natural dyes (see table: Plant sources of natural dye). Widely distributed in the rural belt, these are in close proximity to traditional dyers and handloom weavers. "Organic dyeing not only helps preserve the traditional art of weaving and design but also provides employment and yields economic and ecological benefit," says Kapoor. "Natural dyeing can be a powerful tool to regenerate flora and maintain local biodiversity," he adds.
In some rural areas of Kachcha, Gujarat and Kalahasti, Andhra Pradesh, natural dyer and weaver communities still work together. This also yields benefit for the farmer. Some of the natural dyes like indigo are leguminous and play a role in the crop rotation of rice. "For instance, when synthetic indigo became popular and natural indigo seeds were no longer collected, rice fields lost out on a valuable input by which nitrogen from the atmosphere was fixed in the soil," says M I H Farooqi, former head of phytochemistry at nbri, Lucknow .
"Even flowers, fruits, seeds, leaves, stem, bark, wood and root of numerous dye plants contain colours and are renewable sources. Similarly, the waste after extraction can be utilised as fertiliser," says Kapoor.
The most important plant-based vegetable dyes in India are indigo (Indigofera tinctoria) and madder (Rubia Cordifolia). Even parts of pomegranate (Punica granatum), lac (Kerria lacca), mehandi (Lawsonia inermis), ratanjot (Arnebia nobilis) and turmeric (see box: God's yellow) are used for extracting colours.
However, of the many plant species in India that yield dyes, few have been exhaustively studied for strategic cultivation.
No business drive
We know the potential, we know the opportunity. We have the necessary diversity and the knowhow. But still, not many plants are in use for extraction of dyes in India. Of 40 species of indigo found in India, only 16 yield the dye and only four are commercially grown in India. This is because there are barely any scientific studies on sources of natural dyes. For instance, properties of lichens, a good source of natural dye, are still largely unknown. There is no study to screen the dye bearing capacity of animals. Shell fish and molluscs can also be investigated.
However, there is some scientific activity to use biotechnology to produce synthetic versions of colours (see box: Indigofera tinctoria). There is some work on use of abundantly available forest biomass as natural dyes. "We have experimented and developed knowhow to extract dyes from leaves and bark of eucalyptus, bark of poplar (Populus deltoides), needles and bark of chir (Pinus roxburghii), seeds of Cassia fistula), leaves of Lantana camara and teak (Tectona grandis)," informs Rameshwar Dayal, scientist at the Forest Research Institute (fri), Dehradun.
A target for scientific research are the forests. "We need to do a chemical screening of plant materials in Indian forests, particularly vegetable wastes. Even weeds and different herbs and shrubs should be studied for dye sources. Agronomical practices, chemical modification and purification of dyes is also a research area," suggests Farooqi. Recent studies to improve the efficiency of dyes were carried out at iit, Delhi, iit, Kanpur and nbri, Lucknow. Gulrajani, and Deepti Gupta at the department of textile technology, iit, New Delhi, researched extraction and purification of natural dyes through sophisticated techniques such as chromatography and uv spectroscopy. They are also trying to develop simpler methods of application besides developing pretreatments to improve dye uptake and aftertreatments to improve colour fastness.
Padma S Vankar, head of the Facility for Ecological and Analytical Testing (feat) at iit, Kanpur, investigated the microwave and sonicator systems, scientific appliances based on principles of sound, for extraction and processing of dyes. "We wanted to study the effect of a combination of dyes for dyeing cotton fabric. A mixture of marigold or tessu flowers and pomegranate powder was used for microwave dyeing of cotton using metallic mordants and biomordants, obtained from natural sources," Vankar informs. "Dyeing with a mixture of natural dyes yields excellent colour fastness in cotton fabric. Moreover, sonicator extraction of dyes is much faster and economical than conventional methods," she added.
Kapoor and his team at nbri are involved in screening dye yielding plants, standardisation and extraction through precipitation method, vaccum concentration and spray drying technique. "The work involves standardisation of the dye for good fastness and development of shades using different natural and chemical mordants," says Kapoor.
A Sunrise industry
Five years ago, Ama Herbal, a Lucknow-based company, quick to see potential in the natural dye industry, started to manufacture natural dyes. "The response was tremendous. Everyone asked us for samples within 15 days of writing to them," says Y A Shah, the company's managing director. "But later, everything backfired. There was no business in real terms. Whatever business we receive is from people involved in export or the local carpet industry," he adds.
This about sums up the state of the natural dyes industry today. With the ban on certain azo dyes, there is an international demand for vegetable dyes. Strangely, domestic demand for natural dyes is yet to pick up. The absence of large-scale strategic cultivation of dye yielding plants does not ensure supply of raw material, which makes it difficult to manufacture large quantities of natural dye.
Says Kusum G Tiwari, of Mura Collective, New Delhi , an export company of naturally dyed textiles and clothes, "Getting an export order is easy, but executing it is a problem as it is difficult to get the dyes. Reproducibility of the same colour on a number of clothes is an ordeal," she explains."
Agrees G C Tripathi, managing director of Unique Dyers, a company involved in natural dyeing and export of carpets. "I have worked with natural dyes for the last 10 years and the major problem is shade consistency. A buyer will not accept four flowers in four different shades on four corners of the same carpet. We cannot execute bigger orders if there is no guarantee of colour," he says.
But technology can come to the rescue. Gulrajani agrees that large scale production, necessary to meet hefty export orders, is not possible through the traditional method of processing vegetable dyes. "With super critical extraction carbon dioxide technology and computer matching, one can produce high quality pure dyes of the same shades. But you cannot invest much if you do not have big orders," he explains.
But even with big orders, availability of raw material poses a basic problem. "A delicate balance needs to be maintained between demand and supply as trees cannot be grown overnight. Most natural dyers traditionally use local resources that grow wild. Therefore more land needs to brought under cultivation of dye yielding plants," comments Kapila Himani, secretary of the Society for Indian Natural Dyers in New Delhi.
However, the impact of such findings is still to percolate down to the villages. Most dyers and weavers are in the small-scale industry and stick to traditional methods of dye extraction and processing (see box: Design tradition) . "We still use traditional dyes in the same way, as our forefathers," says Derawala. "We prepare the black colour from jaggery (gur) and iron. The green or hara dhania colour is made from indigo, turmeric and pomegranate rind. We feel totally isolated. We need more information about raw material sources for different colours. We need to improve the fastness of natural colours and increase their acceptance in clothes. But who do we turn to?" he asks. Villages like Bagru, involved with natural colours are on their own. "The village receives no help from the government or any other institution," complains Derawala. Natural dyers are reluctant to produce more dye as there is no market guarantee of local uptake. "Local consumers do not want natural dyes,"he comments.
He has hit the nail on the head. Natural dyes will continue to remain a sunrise sector unless domestic consumers wake up and demand naturally dyed textiles.
Pasha and her friends love to wear clothes dyed with vegetable colours. "The colours bleed during the initial washes. But washing the clothes separately is better than having chemicals next to your body," asserts Pasha.
Obviously, not many people in India accept this. According to a study by the Uttar Pradesh Industrial Cooperative Society, (upico), Kanpur, growth in the use of natural dyes in India, was only felt in the carpet and woollen clothes sector followed by silk saris.
Domestic demand is stagnant. According to Farooqi, "Clothes dyed with natural colours are costlier by 25-35 per cent. Indians cannot afford it but Europeans can. Therefore, natural dyes are not going to take the country by storm, but the export market will surely grow. In the next five years, Europe and us will buy in a major way."
Import of natural dyes by these countries has increased ever since the ban on certain azo dyes in 1996. In 1998, import demand for natural dyes in the us increased to $41 million, a hike of 70 per cent since 1994. The European import market also touched a high of us $70 million in 1998, an increase of 46 per cent from 1994. But, India's share was a paltry export of us $6 million and us $ 5.5 million to us and Europe respectively (see table: Natural products).
"Commercialisation of natural dyes can be successful only with a systematic and scientific approach to extraction, purification and promotion of use of natural dyes," Vankar said. In India, consumer demand is restricted by pricing, shade availability and colour fastness. "The need of the hour is certification from the government that our clothes are coloured with vegetable dyes," suggests Prabha Nagarajan from Indigo India, a Chennai-based organisation.
Meanwhile, in cloth-dyeing centres like Sanganer in Rajasthan, or Tirpur in Tamil Nadu, natural dyeing would be on a limited scale with all products being meant for "100 per cent export." We need to wake up to the call of nature.
|Dye brand name||Plant source||Price
(Rs. per kilogramme)
|Alps Industries, Sahibabad|
|Ama Herbal, Lucknow|
A P Mitra couldn't believe it. He along with 200-odd scientists from India, Europe, Maldives and the us was conducting an intensive six-week field experiment in 1999 to study the effect of airborne tiny particles called aerosols on climate. The tropical Indian Ocean, where clean air from the southern Indian Ocean including Antarctica and not-so-clean air from the Indian subcontinent meet, provided a unique natural laboratory for this experiment that involved the use of ships, aircrafts, balloons and satellites. As the results started pouring in, the scientists were in for a shock.
A thick extensive haze layer roughly seven times the size of India had enveloped the northern Indian Ocean. "The haze extends to over 10 million square kilometres (km)," says Mitra of the Delhi-based National Physical Laboratory and one of the three co-chief scientists of the Indian Ocean Experiment (indoex). The Centre for Clouds, Chemistry and Climate at Scripps Institute of Oceanography, University of California, San Diego, coordinated the us $25 million project, 60 per cent of whose funding came from us agencies including the National Aeronautics and Space Administration (nasa).
Seen 1,600 km off the coast, the haze extends from the ocean surface to altitudes of one to three km. Most of the northern Indian Ocean, including the Arabian Sea, much of the Bay of Bengal, and the equatorial Indian Ocean to about 5 south of the equator remains shrouded by the haze throughout the experiment. The Northeast monsoon -- the winter -- transports the haze thousands of miles to the Indian Ocean. Such high concentrations of pollutants less than a few micrometre in diameter were not seen earlier in these regions. Nor was its effect on rainfall known.
"The haze could have a serious effect on rainfall and the onset of monsoon through its influence on cloud formation," says Mitra. And for a country like India, aerosols could very well be playing a critical role on the onset of monsoons over different regions. "Western and north-western India is becoming drier while eastern and southern India is becoming wetter," adds Mitra. It doesn't just stop there. From affecting agricultural yield to causing asthma, the frightful effects of aerosols are only now beginning to surface.
Aerosols are particles about a millionth of a centimetre in diameter, consisting of sulphates, soot, organic carbon, and mineral dust and are produced both naturally and by human activities. Commonly known as 'suspended matter', aerosols are best described as tiny liquid or solid particles floating in the air. About 90 per cent of airborne aerosols are naturally occurring substances like dust and particulate matter from volcanic eruptions, and sea spray. Overall, humans are responsible for roughly 10 per cent of the aerosols, mainly as exhausts from automobile, industrial, and biomass burning. In the Indian Ocean study, however, scientists inferred that as much as 85 per cent of the aerosols were of "anthropogenic origin".
Aerosol sources are of two types -- primary and secondary. Primary aerosols are emitted directly as tiny particles, such as smoke from bush or forest fires, soot from burning fossil fuels in industries, vehicles, trains, airplanes, airborne dust and sea-salt particles produced when sea spray dries out. Secondary aerosols are produced from gaseous precursors. Chemical reactions in the air, converts the primary gaseous pollutants -- like sulphur dioxide and nitrous oxide -- into gases with lower volatility, some of which condense into particulates. Sulphur dioxide pollution from power plants or other industries, converts into sulphate particles, for instance. Emissions from vegetation and marine organisms also form secondary aerosols in the atmosphere. The resulting product then nucleates to form new particles or condenses on pre-existing particles (see box: Aerosol triggers).
These tiny particles can range in size from 0.01 micrometre to several tens of micrometre. For example, particles in cigarette smoke are in the middle range and typical cloud drops are 10 or more micrometre in diameter. Under normal circumstances, the majority of aerosols form a thin haze in the lower atmosphere where they are washed out by rain within about a week. A severe volcanic eruption on the other hand can put large amounts of aerosol into the upper atmosphere. Since it does not rain there, they can remain in the same place for many months, creating beautiful sunsets, and possibly causing summer temperatures to be cooler than normal by blocking out sunlight.
Scientists estimate that in 1991, Mount Pinatubo in the Philippines injected about 20 million tonnes of sulphur dioxide into the atmosphere, cooling average global temperatures over the following year by about half a degree. But aerosols do not always have a cooling influence. Emerging evidence supports the case for aerosols also having a warming effect. It is this push and pull impact of aerosols that befuddles climate science.
Fine aerosol particles of both primary and secondary origins can affect human health, reduce visibility and influence climate both directly and indirectly. Since aerosols reduce the amount of sunlight reaching the Earth's surface, they could have an adverse impact on agriculture and water resources. Moreover, settling of aerosol particles like black carbon and dust on plants can shield leaves from sunlight. Such a deposition can also increase acidity and affect plants. Children and elderly people inhaling the polluted air replete with these aerosols are at a greater risk of developing respiratory diseases.
indoex began in 1996 and was conducted over four years during the winter season. In winter, before the Indian summer monsoon, the surface wind flows in the northeast direction over the Indian subcontinent and the surrounding region. These winds help in transporting a number of suspended particles from the continent to the ocean surface. The polluted northeast winds cover almost the entire region lying north of what is known as the Inter Tropical Convergence Zone (itcz). Bound by the landmasses of Arabia, Africa in the west and the Southeast Asian regions, Myanmar, Thailand, Malaysia in the east, itcz is an area of low pressure situated near the equator where northeast winds meet southeast winds. At the same time, on the south of itcz, the air is relatively pristine and almost uninfluenced by continents.
The indoex project found that the quantity of particulate matter found hundreds of kilometres away from the source over the Indian Ocean was comparable to suburban air pollution in North America and Europe. Chemical analysis of the haze has revealed that as much as 85 per cent of the giant haze layer was due to human made aerosols with anthropogenic sources like fossil fuel burning, industrial emissions and biomass burning. The composition of particulate matter was quite uniform over the northern Indian Ocean. A typical pollutant particle originating from an anthropogenic source consisted of 10-15 per cent of black carbon, 26 per cent of organic, 32 per cent of sulphate, 10 per cent of mineral dust, five per cent of fly ash and smaller fractions of other chemicals. Black carbon and fly ash are human produced, and sulphate can also be attributed to anthropogenic sources to a large extent. Black carbon particles were always mixed with organic compounds and sulphates (see graph: Of black carbon...) .
Further evidence of the extent of pollution came from measuring aerosol optical depth (aod) values for the northern and southern Indian Ocean. aod is the approximate number of aerosols in a vertical path through the atmosphere relative to the standard number of aerosols in a similar path through a clean, dry atmosphere at sea level. Measurements taken by the Indian vessel Sagar Kanya during January to March from 1996 to 1999 showed that aod varies from about 0.05 (typical of unpolluted air) in the southern Indian Ocean to between 0.4 and 0.7 (very polluted) north of the equator over the Arabian Sea and the Bay of Bengal (see graph: Crowded region). The haze also disturbs the self-cleaning efficiency of the atmosphere by reducing the amount of hydroxyl radical (oh), a major oxidising chemical in the lower atmosphere. Most gases and air pollutants emitted into the atmosphere by human activities and natural processes and involved in ozone depletion or global warming are removed by reacting with oh.
The black carbon content of the haze was high, making it highly absorbant of sunlight. Depending on the type and composition of particulates, they scatter or absorb solar energy in the atmosphere. Sulphates and nitrates are known to scatter sunlight back into the space, thus reducing the amount of energy absorbed by the Earth and cooling it. Black carbon or soot particles heat the atmosphere by absorbing solar energy due to their darker colour and hence warming the surrounding air.
Observations and results from indoex are being fed into various climate models to study the impact of the vast stretch of pollution over the Indian Ocean on temperature, rainfall and hydrological cycle. The models are general circulation models (gcm) with fixed ocean temperature (gcm-fo), mixed layer ocean (gcm-mo) and fully coupled ocean model (gcm-co). The results are indicative of a much larger phenomena over the Indian Ocean and its wind circulatory systems, say scientists.
Aerosols may be reducing rainfall and threatening the Earth's fresh water supplies, according to the Scripps Institution of Oceanography, San Diego. "Initially we thought that aerosols were mainly a cooling agent, offsetting global warming. Now we find that these have a big impact on the water budget of the planet," said Scripps professor V Ramanathan, in a study published in 2001 . Based on satellite data from nasa and indoex, scientists have found that tiny particles of soot and other pollutants are affecting the planet's hydrological cycle far more than previously understood. The indoex findings are limited, because they are restricted to the dry season, from December to April. Scientists want to now study how the solar heating in the haze affects the monsoon rainfall. But what they already know, should cause us to think hard.
While tiny particles suspended in the air are essential for cloud formation, if they are too many in number, it may adversely affect rainfall (see box: Heavy cloud). In polluted areas in Thailand and Indonesia, clouds do not precipitate due to very small droplet size, whereas they precipitate in less polluted areas within about 10 to 15 minutes after their formation.
According to the indoex models (gcm-fo and gcm-mo), the haze causes a 1-2 per cent decrease in tropical average evaporation and precipitation, depending on the season. Model simulations also show that the haze causes significant redistribution of rainfall in the indoex region. While some regions experience as much as 20-40 per cent increase, others suffer comparable decreases (see map: Changing pattern of rainfall). For instance, gcm-fo shows haze leading to a large increase in rainfall over southern India with a large decrease in winter rainfall over parts of northwest India, Pakistan and Afghanistan. Areas over the western equatorial Pacific are also getting dry.
Effect of particulates on cloud properties could also be influencing the arrival of monsoon and its distribution in India, according to Mitra.
"Observational evidence about decrease in the size of cloud droplets with increase in aerosol amount, and decrease in rainfall over the Sahelian region correlated with the increase in dust, show without doubt that aerosol has a strong influence on clouds and precipitation," says A Jayaraman of Physical Research Laboratory, Ahmedabad, who has studied the effect of aerosols on monsoons. "If it can happen in other parts of the world why not over India? The problem is that we do not have observational evidence," adds Jayaraman. "Some scientists may argue that the monsoon is such a strong system and nothing can happen to it. But we should not forget that our pollution is also equally strong."
In 1995, a report published by the Intergovernmental Panel on Climate Change (ipcc), an international body of scientists, recorded some aerosols as having a cooling effect. Since then understanding of aerosol impact have undergone a sea change. By 2001, ipcc had gathered enough evidence to support the case for aerosols having a warming effect. Warming due to black carbon aerosols may, in fact, balance the cooling effect of sulphate aerosols -- the single largest contributor to cooling by particulates. The proportion of light scattered by aerosols to that absorbed determines their warming or cooling influence.
At the same time, aerosols reduce the heating of the Earth's surface as they decrease the amount of solar energy reaching the surface by absorbing or scattering it. The Indian Ocean haze, with as much as 10 to 15 per cent black carbon, is known to reduce the surface solar heating by about 10 per cent, while nearly doubling the lower atmospheric heating. The haze has led to a cooling of about 0.3c over the Indian subcontinent since the 1970s, says the indoex findings.
An indirect effect of aerosols on the amount of incoming solar energy is through their influence on cloud formation. They can enhance the possible cooling effect of clouds. Dense clouds containing many small droplets if the air is overcrowded with aerosols, reflect the most sunlight back into space, causing more cooling. More droplets mean more surface area to block the light.
While scattering of light by aerosols can be measured fairly accurately, assessing absorption by soot remains a challenge. Soot is a very complex material built up of a number of nuclei. As its three-dimensional structure is not known properly, it is not easy to calculate the light absorbed by it. Moreover, it is impossible to characterise each and every source of aerosols. Only one instrument, the photo acoustic spectrometer, directly measures absorption by particles suspended in the atmosphere, but it has not been used widely. In practice, therefore, the absorption by all particles together is measured, but this is not a sufficiently sensitive method. Also, the process of collecting particles to measure absorption alters their structure, and it is not known as to how different the measured value may be from the actual absorption.
Moreover, it should be known precisely how black carbon is mixed with other particles in the aerosol. This is important as soot particles embedded in a sulphate aerosol can absorb up to twice as much light because the sulphate acts as a lens.
The presence of haze can affect agricultural production, as it cuts down the total amount of sunlight reaching the Earth, which in turn reduces photosynthesis in plants. Moreover, settling of aerosol particles like black carbon and sulphate on leaves can further decrease the amount of sunlight absorbed by the plant for its growth. Such a deposition can also increase acidity, which is again harmful for plants. Another significant effect could be the suppression of rainfall by the haze.
In one of the first attempts to estimate the impact of the south Asian haze on Indian agriculture, a crop model has been developed by the Indian Agricultural Research Institute, New Delhi. The haze is observed in winter and rice is the dominant winter crop in south India. The model showed a decrease of about 5-10 per cent in rice crop productivity when reduction in sunlight due to the presence of haze was considered (see graph: Cropped!). The yield of sugarcane, an important cash crop in the country, also decreases. For the crop sown in October-November, the decrease could be around 1.5 per cent, as the reduction in sunlight would occur during important stages of the plant growth.
Scientists are yet to unravel all the mysteries about the tiny and yet complex three-dimensional particles. Key details about their properties and their effects remain elusive. So far, it has not been possible to make reliable measurements to determine their distribution and properties on a global scale. Large uncertainties remain in estimating the magnitude of various aerosols emitted from different sources. Studies based on indoex data are quite preliminary in nature, however, latest results provide an indication of their potential to impact climate scenarios, rainfall and agriculture.
The indoex experiment showed that aerosols could be transported to long distances away from the emitting region. Soot lodged in sub-micron sulphate and organic aerosols was seen in distant south showing that these have a lifetime of over a week. The project also fuelled doubts about similar large-scale transport of pollution occurring in other regions of the Earth. Pollutants from Asia are being transported across the Pacific Ocean by winds. Massive dust storms in Asia, which also carry sulphate and organic aerosols, transport soil eastward to Japan and across the Pacific to the us.
However, developing countries have borne far worse consequences of industrialisation than the Northern countries. A recent study by Leon Rotstayn and Ulrike Lohmann, Dalhousie University, Australia, has revealed that sulphate aerosols formed upon oxidation of sulphur dioxide emissions from industries in North America and Europe may have been responsible for causing severe droughts in the Sahel region of Africa in the 1980s. Precipitation in this region has fallen by between 20 and 50 per cent in the last 30 years. Also, these emissions may have led to a greater rainfall in Australia as the tropical rain belt shifted southwards (see map: A season of drought).
On the other hand, dust storms from Africa's arid Sahelian region, which can rise up to four kilometres into the sky, travel across the Atlantic Ocean to Florida and put about 500 million to 1 billion tonnes of dust into the atmosphere. The incidence of dust clouds reaching Florida has increased since the drought in the Sahel region.
Transcontinental dust clouds originating from Asia and Africa are the most significant for North America as itcz along the equator acts as a sort of wind barrier to separate the storms of the Northern and Southern Hemispheres. The Sahel region, the Sahara desert, the Indus valley in India, the Taklimakan desert north of the Himalayas and the Gobi desert in Mongolia, are a few main sources of dust in the world. Surface wind blowing at high speeds over the desert and low sparse grassland regions in Mongolia and western China can inject enormous plumes of dust high into the atmosphere. These are then transported as far as the Pacific Ocean basin before being depleted by rain or gravitational pull.
Compared with the clouds from Africa, Asian dust shows higher concentration of human caused air pollutants such as sulphates, perhaps due to Asia's dense population and industrial cities. For instance, dust storms from the Mongolian region start from severely eroded soils, due to overgrazing and overfarming, and as these dust clouds pass over Beijing and other large cities, they gather industrial pollutants.
Apart from the health effects associated with particulate matter, mineral constituents of dust present an added hazard (see box: Killers at large). Fine iron particles, which give the reddish tinge to the African dust, can generate hydroxyl radicals on the lung surface, which can scar lung tissue over time and decrease its effectiveness. Another important feature of transcontinental dust clouds is the microbes they transport. Initially it was believed that ocean distances were too large for bacteria to survive, but research points that intercontinental dust may transmit viable pathogens. In thick clouds of dust, the uv exposure at the bottom can be just half of that at the upper surface, so microbes in the lower layer can be protected and can survive the transport.
Pathogens carried in dust can cause skin infections such as rashes and open sores, and may affect crops like cotton, peaches and rice. Indirectly, dust aerosols can impact nutrition by reducing crop yields -- through erosion of soil nutrients and by shading crops from needed uv light. They also cause allergic reactions and diseases.
Lifetimes of most anthropogenic aerosols are in the range of 5 to 10 days. If aerosols are mostly confined to an altitude of one kilometre, they can travel about a thousand kilometre in so many days. But when lifted to higher layers, like in case of the indoex haze where maximum concentration of aerosols was at about three kilometres, aerosols can travel half way around the globe within a week.
While emerging research has answered some questions, many nagging ones remain unanswered. Does the haze balance the warming due to greenhouse gases (ghgs) or does it intensify it? How does air pollution from Asia affect worldwide concentrations of pollutants? Since indoex was conducted during January to March, there is no data on the extent of the haze during the rest of the year. Scientists like Mitra caution that a lot more research is needed on the effect of haze on monsoons, effect of reduced sunlight on water budget and soil moisture to be able to make any conclusive statements. He suggests a holistic policy framework taking into consideration ghgs, aerosols and short-lived gases to emphasise interactions between global processes like warming of the Earth due to ghgs and, local and regional processes like air pollution (see chart: Pollutants at work). In short, we need to learn more. But we also have to act on the basis of what we know today.
Some people are beginning to think that the heat absorbing soot is a godsend as it may help to reduce global warming. Nothing can be further from the truth. As scientists working on indoex show, the short-term fix of aerosol cooling could well be deadly for the regional climate -- its rainfall and sunlight. By making the region, more drought-prone, it could act as a double-whammy, with vulnerable people becoming even more vulnerable to the impacts of global climate change as they occur.
But as Mitra says, it is important to distinguish between the causes and impacts of greenhouse gases, with lifetime ranges of decades to centuries, from aerosols. However, this should not take away from the need to learn more about the impacts of aerosols -- on the health of people to the health of our local climate system.
Interestingly, the action agenda, in both cases, greenhouse gases and regional haze is complementary -- to reduce emissions from fossil fuel burning. But the actors will be different. In the case of global warming, the first accused, is the industrialised world, which is continuing to emit, far beyond its share of the global atmospheric space. Its emissions -- from its era of industrialisation, have added to the concentration of gases in the atmosphere. This historical or grandfathering of the atmospheric pollution load, is what is creating the problem today. Developing countries have little space for economic development. Climate change policy is, therefore, about creating the ecological space for developing countries to grow, by limiting the emissions of the industrialised world.
In the case of regional haze, the accused are the users of fossil fuel in the developing world -- from thermal power plants, to automobiles and to burning of biomass. The 'survival' emissions of the poor -- to burn firewood to cook food -- cannot be compared with 'luxury' emissions of the rich -- to drive a car, for instance. Therefore, in this case, the onus of change lies with the rich of the fast developing world. We have to recognise, and fast, that air pollution is doing more damage than just killing us softly.
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