Deadly Particles

They are tiny and deadly. Recent research has brought to light the existence of airborne particles so tiny they defy measurement. Toxic particles so minute as to be almost intangible. Though evidence is piling up increasingly on the lethal effects of particles, scientists are yet to fathom the extent of damage they can cause to public health. Meanwhile, these tiny killers continue to take more lives and send an increasing number of people to hospitals and emergency rooms. With the Indian government hardly bothering to respond, a dirty cloud of haze promises to blanket India's next millennium

 
Last Updated: Sunday 07 June 2015 | 21:11:47 PM

Deadly Particles

-- Concern over particles

That airborne particles kill has been known for a while. But the threat is rising with every scientific discovery

There is nothing new about particulate pollution. Yet, scientists are talking about airborne particles today like never before. As science on air pollution developed in response to environmental and public health crises in the West, these tiny killers came under intense scrutiny. Today, scientists are perplexed by the discovery that even at very low concentrations these particles kill. They have now shifted their focus to the tiniest and the most lethal of them all and their potential to claim lives. This has dramatically altered the approach to its risk management worldwide.

Scientists had known all along that particles are harmful but scientific evidence on the enormity of their health effects is yet to be understood completely. The history of particles goes back many hundred years. Records tell us that during the rule of Edward I (1272-1307 ad) burning of coal was banned in London to control air pollution. His successor Edward II actually ordered persons guilty on this count to be tortured. As the West industrialised and motorised fast, it went through a series of severe air pollution episodes in the early 20th century. Smoke particles and sulphur dioxide were the most talked about pollutants in those days. The first recorded episode was in Meuse valley of Belgium where air pollutants got trapped at ground level for a week in December 1930 killing 60 people. Across the Atlantic, in October 1948, half the population of 14,000 in Donora, Pennsylvania, fell sick, 10 per cent fell severely ill and 20 died due to severe air pollution. But it took the notorious London Smog of 1952 which killed 4,000 people to trigger extensive research on air pollution and its effects on health which ultimately revealed deadly facts about smoke particles.

When the uk government, alarmed by the death count of the 1952 smog episode in London, enforced more stringent air pollution control methods, they actually succeeded in bringing the level of pollution down. Paradoxically, this success in lowering pollution only proved that the objective of reducing risk from the killer particles was still very distant.

Immediately after air pollution levels fell in London following strict enforcement of air pollution measures, it first became more and more difficult to detect the effects on health of day-to-day variation in concentration of smoke. Robert L Maynard of the department of health, uk, who has recently edited a study entitled Particulate Matter: properties and effects upon health , says that this led scientists to believe that it is possible to set a threshold limit for pollutants below which health effects are unlikely to occur. Therefore, setting safe limits for air pollutants was the most obvious thing to do. This led to establishment of guidelines for air pollutants including particulates in uk and these later provided the basis for the World Health Organisation's Air Quality Guidelines for Europe in 1987 and air quality regulations worldwide.

But things changed dramatically when scientists began to observe incomprehensible but serious health effects even at extremely low concentrations of particles. Says Maynard, "A trickle of epidemiological studies that began in the late 1980s and turned into a flood gate in the 1990s provided evidence that day to day variations in the already low concentrations of particles and other pollutants were still associated with effects on health."

As science on particles developed, scientists were faced with more questions than they had solutions for. It was clear to them that they needed to understand much more about the 'idiosyncrasies' of ultrafine particles and how they chemically and biologically affect human health systems. Only further research and knowledge will enable scientists to identify the most dangerous of all particles and concentrate their efforts towards controlling them.

A close look at particles

Small and dangerous: Ultra-fin even at low concentrations, airborne particles are lethal: T he great puzzle was if air pollution levels had visibly and measurably been vastly improved, how could they continue to have such detrimental effects on health? By the late 1970s, studies conducted in the us found that health damage was more strongly associated with particulate and not with sulphur dioxide.

This defied reason. Toxicologists were at a loss to explain how even small doses of particles, as shown by the results of the new studies, could have any harmful effects, let alone death. For a long time many scientists were doubtful of the result and this led to many acrimonious debates on the issue. However, eventually these new studies proved wrong everything that was earlier said or believed about there being no possible harmful health effects below a certain level of concentration.

Even more interesting is that the scientists are looking for an answer not only in the chemical properties but also in the physical property of the particles, which, simply put, means the size of a particle. Says Maynard, "This has shifted the debate in a new direction as it was suggested that very small particles might be playing the role."

Explains Anthony Seaton of the University of Aberdeen, uk , who has researched airborne particles and their health effects, "A clue has come from the consideration of the size distribution of particles produced when fuel is burned and a realisation that the smaller they are, the greater their surface area. Therefore, their potential to carry toxic elements deep into the lung increases. The greater majority of these particles are less than 1 micron (one-fiftieth the diameter of a human hair) in diameter and most fall in the size range of 20-100 microns -- being so small in size they penetrate deep into the lung." This simply means that as the size of the particles get smaller and their number increases, other toxic chemicals in the emissions get more surface area to cling to and, therefore, become more lethal. Maynard states that "studies have shown that carbon black have very different and more toxicological properties when presented as ultrafine." Thus, the scientific focus is getting more microscopic, looking for particles smaller than one-millionth of a metre.

Minimal increase in particulate levels can have adverse health effects: Scientists now believe that even a very small increase in concentration in particles can cause great harm. Says Anthony Seaton, "Despite the considerable reductions in the concentrations of particles in urban air, it has been recognised that increases in deaths and illness still occur in relation to rise in the level of particles in the air of major cities." There is a scientific consensus that very small rises in concentrations even from a baseline level of 30 microgrammes per cubic metre (g/cum) can be associated with measurable increases in death rates and hospital admissions.

Such evidence has disturbed the Western world. Though the West has been successful in keeping the peak levels of particles close to the air quality standards, they do not feel safe anymore. According to Shankar Prasad, community health adviser to the California Air Resources Board ( carb ), the pm 10 (particles with a diameter of 10 microns or one-fifth the width of a human hair) level for most part remains close to the who guidelines of 70 g/cum and rarely reaches 170-200 g/cum. Yet particulate matter is one of the important parameters for issuing smog alerts to warn citizens about the dip in air quality on a daily basis. Richard Wilson of the Department of Physics and Centre for Risk Analysis in the Harvard University, warns that the consistent picture that a us public health authority should consider is that 60,000 people might be dying prematurely due to problems related to air pollution in the us each year.

Smaller particles
Small particles are typically designated according to size. Studies on particle size now show that particles in the ambient air range from 0.01 micron to 100 micron in diameter (one micron is one-millionth of a metre). Particles in the 0.1-2.5 micron range are considered 'fine'. In fact, particles 10 micron in size are not even treated as fine particles any longer. Smaller the particle, greater the risk: The size of the particles now assumes vital importance from the environmental point of view as that would determine how long the particles would remain airborne and also from the point of view of their impact on human health. The size of particles determine how deep they can penetrate our lungs.

Bigger particles settle fast due to gravity. The fine particles remain in the air for a time period ranging from days to weeks and can be carried by wind for thousands of kilometres. On the other hand, coarse particles take minutes or even hours to clear and cover distances of 1 to 10 km.

Scientists are no longer bothered about coarse dust particles, which are largely from natural sources. They are more worried about the tiny chemical particles from fuel combustion which are extremely small in size and go deep into the lungs, staying there longer and causing maximum damage. The smaller they are, the greater their ability to penetrate deeper into the respiratory tract (see box: Tinier they are, deeper they go ).

Deadly cocktail
Particles are dangerous because they carry a very complex mixture of toxic pollutants. They are produced by diverse sources, vary in size and chemical composition, and contain large numbers of both organic and inorganic compounds. Scientists at the Health Effects Institute (hei) in Boston, usa, have found that the nature of mixture varies from place to place and over time. Yet, similar effects of exposure to particulate matter have been reported by epidemiological studies based on day-to-day observation conducted in a variety of locations where the relative amount of pollutants and associated pollutants are different. This has puzzled the hei scientists. They now want to know what attributes of the particulate mixture may be important in causing toxicity, and what factors affect an individual sensitivity?

Chemical coating makes the particles dangerous: John Spengler of the Harvard School of Public Health points out that the fine particles from burning of coal, petrol, diesel and wood are a complex mixture of sulphate, nitrate, ammonium, hydrogen ions, elemental organic compounds, metals, poly nuclear aromatics, lead, cadmium, vanadium, copper, zinc, nickel, and so on. It is this cocktail of chemicals which makes these tiny killers so lethal (see box: A matter of size ). The harmful chemicals present in the emissions coat the surface of these tiny particles. When these particles penetrate the respiratory tract, these toxic substances trigger serious health problems.

Diesel particles
Scientists have paid a lot of attention to particles emitted by diesel engines. In recent years, the composition of diesel particles has been the focus of increased scrutiny as diesel vehicles are known to emit extremely small particulate matter. A recent study in the uk has found that 90 per cent of the particles emitted by diesel vehicles one micron in diameter or smaller and are thus highly respirable. It has been further proved that diesel exhaust has a larger quantity of fine and ultra-fine toxic particles in comparison to particulate matter in which there is a total absence of diesel exhaust.

Characteristics of diesel particles: Moreover, particles from the exhaust of diesel engines (simply called diesel exhaust) have a carbon core which is unique to them, as are some of the organic compounds that these particles absorb like the polycylic aromatic hydrocarbons (pahs). Besides particulate matter, diesel exhaust also contains toxic gases. Both these components -- particles and gases -- in the diesel exhaust contain hundreds of lethal chemical compounds, including organic compounds. Further, these components of a diesel exhaust have toxicological and carcinogenic properties that pose a serious health hazard for humans.

Sulphate particles
The atmosphere plays its own role in aiding the formation of deadly particles -- especially sulphate particles. Sulphate particles are also emitted due to combustion of fuels with high sulphur content like fossil fuels. Diesel is a major source of sulphate particles. Most fossil fuels contain sulphur, which forms sulphur dioxide (so2) when burnt. Once it is out in the atmosphere so2 is further oxidised and turns into sulphate particles. These can be carried to considerable distances through the air. Sulphate particles are now treated as more dangerous than pm10 and pm2.5 particles.

Components of sulphate particles: While some so2 oxidises to form sulphate particles, some reacts with hydroxyl radical (oh) to form sulphur trioxide and then, again, it gets transformed into fine droplets of sulphuric acid in the presence of moisture. Sulphuric acid droplets can again react with other gases to form sulphate particles. The fine aerosols of sulphuric acid form droplets that are in the nanometre range of size. These exceedingly small droplets then grow a little bigger through thickening by coalescing with other sulphuric acid droplets or with other suspended particles in the air. But their size remains below one micron. Since it takes time to oxidise, sulphate particles can appear in locations far away from the source of the precursor gas, thus making even less polluted areas in the urban periphery vulnerable to its deadly effect.

Health risks posed by sulphate particles: Latest information available from the who implicates sulphates as being a major causative factor in increasing hospital admissions and even mortality. Specifically, an increase of 10 g/cum sulphates can cause an increase in hospital admissions and daily mortality to be as high as 50 to 60 per cent (see graph: The health effects ). Researchers found that summertime hospital admissions in Ontario for children are associated with increases in ambient levels of sulphates and ozone. No data on sulphate levels in India is available, but given the scale of diesel consumption it could be high.

Constraints on monitoring
While scientists are increasingly discovering health effects of tiny particulate matter, air quality regulators are yet to catch up and come up with risk management plans. Maynard is convinced that "the rate of development of thinking in the area of particle toxicology and epidemiology has posed problems and regulations are behind the leading edge of science." "This has been especially the case regarding the optimal metric (measurement) that should be chosen to reflect the concentration of particles in the air. In a number of countries, including the uk, attention was focused on pm 10, but pressure to move to pm 2.5 and even pm 0.1 is mounting. Also, just measuring the mass of particulate matter is not enough; we need to monitor the number of ultra fine particles," he explains.

Measuring the tiniest of them all: So, what should be the size of particles that are monitored to estimate the risk from particulate pollution? This is a matter of great debate across the world.

The West has so far responded by shifting focus from the monitoring of total suspended particulate matter (tspm) which includes dust, to particles of size less than 10 micron and 2.5 micron. Till about 1987, tspm was the only available measurement of particles in the us. But after 1987, the United States Environmental Protection Agency (epa) started monitoring only pm 10.

In 1997 the epa issued standards for pm 2.5. Scientists now believe that particles get more volatile and toxic as they get smaller than 2.5 microns. Some scientists now hold that the decision to measure pm 10, or for that matter pm 2.5, to represent the small particulate pollution levels in cities is arbitrary and may still fail to estimate the real risk from even tinier particles. According to Lidia Morawska, associate professor with the department of physical sciences at the Queensland Institute of Technology in Brisbane, Australia, the cut-off point at pm 2.5, set by the epa, was determined by the technology that was available to measure such small particles. The decision was arbitrary as appropriate instruments to monitor the ultrafine particles were not available. So there is no clear scientific reason to base standards on pm 2.5. According to Morawska, there is a need to take into account the ultrafine particles smaller than 2.5 microns. Here the number of particles goes very high and can be determined only with the help of very sophisticated gadgets, which are still in the making. The size now in focus is 0.03 microgramme. Clearly, technical limitations have constrained monitoring of pm 1 and smaller particles.

Particles smaller than 1 micron: Mary Amder, professor of toxicology at the Harvard School of Public Health in the us informs that a study by scientist K Dreher and others, has collected samples of ambient particles in the size range: smaller than 1.7 micron, between 1.7 and 3.7 micron, and between 3.7 and 20 micron in Washington, dc. The study found that particulates smaller than 1.7 micron had the highest percentage of soluble metal content, the highest sulphate content and were the most acidic of the three size fractions. In animals exposed to these particles, greatest lung damage was caused by the particles smaller than 1.7 micron.

The epa now recognises the need to monitor pm 1. Says Dale Evarts from the department of air pollution planning and standards at the epa, "There is no routine monitoring but epa is sponsoring studies in 10 cities that include measuring of these particles (pm 1s)."

Health is first priority: R L Maynard says that arguments over the health effects of particulate matter has been quite "ill-tempered". One reason is that industry representatives saw that demands for cleaner operations and products would follow this new science on particulate and realised that these would be both difficult to meet and very expensive. And he was proved right when epa proposed revision of national standard for pm 2.5 from 65 g/cum to 50 g/cum as 24-hour average in November 1998. Since this would require reductions in pollution from automobiles, power plants and industrial facilities, the proposed standards drew considerable opposition from the industry and the standards have been challenged in us courts. Though the decision on the proposed standard is still pending, epa has estimated that implementation of the proposed standard could cost $8.6 billion per year, but health benefits of implementing the new standards would outweigh this cost by a factor of 2-11.

However, the American Lung Association ( ala ) still feels that the new standard is not adequate to protect public health. In their report, entitled Gambling with Public Health II , the ala has said that the "proposed pm 2.5 ambient standards of the epa would still potentially expose 89 million people to serious health hazard". Instead they want the standard of 18 g/cum averaged over 24 hours, and 10 g/cum annually. The important message is that usa is prepared to take up such high cost abatement programme where even at the worst case scenario the pm 10 levels peak to only 170-200 g/cum, and that, too, rarely, compared to more than 800 g/cum in Delhi.

A matter of size
The sources of particles render them unique

Sizeof particles
Down to Earth

TOTAL SUSPENDED PARTICULATES (TSPM)
Source: Resuspended dust, soil dust, street dust. Coal and oil fly ash. Metal oxides of Silicon, Aluminium, Magnesium, Iron. Mold spores and pollen.
RESPIRABLE SUSPENDED PARTICULATE MATTERS (PM 10)
Particles less than 10 microns in size

Source: Wind blown dust and grinding operations. Fog droplets, pollen, bacteria.
FINE PARTICLES  (PM 2.5)
Source: Diesel exhaust. Combustion of Coal, Oil, Gasoline. High temperature processes, smelters, steel mills etc. Coal-fired thermal power plants.
PM 1.0 (ULTRA FINE PARTICLES)
Source: Diesel exhaust. Combustion of Coal, Oil, Gasoline, Wood. Atmospheric transformation products of NOx, SO2 and organic compounds.


Strict control
The air quality standards for PM10 set by international agencies

  AGENCY STANDARD TIME PERIOD
  ALA (proposed) 10 g/cum   Annual average
  ALA (proposed) 18 g/cum   24-hour average
  California 30 g/cum   Annual Geometric Mean
  US EPA 50 g/cum   Average annual ambient standard
  California 50 g/cum   24-hour average
  United Kingdom 50 g/cum   24-hour average
  Indian Standard 60 g/cum   Annual average
  WHO 70 g/cum   European Ambient Air Quality Guideline
  Indian Standard 100 g/cum   24-hour average
  US EPA 150 g/cum   24-hour average

Source: Mary Amdur et al 1996, in Richard Wilson and John Spengler (Eds) Particles in Our Air — Health Effects and Concentrations, Harvard University Press, USA
ALA: American Lung Association
US EPA: United States Environmental Protection Agency
WHO: World Health Organisation

Note: All figures in microgrammes per cubic metre (g/cum)

Relevance to India

The aiims emergency room daily receives about 150 patients. Over 100,000 patients were examined for the study, which focused on patients with aggravated symptoms of asthma, chronic bronchitis and heart ailments. The study found that tspm was highest in November and December; and, so were the hospital admissions. Number of patients reporting with cardio-respiratory problems increased sharply in these two months and declined rapidly in the following months when the tspm levels dropped. The fact that admissions declined in January showed that cold weather alone was not responsible for increase in heart ailments.

Otherwise, the only study on air pollution and human health in India came from the World Bank in 1995. This study had categorically stated that small particulate emissions, like pm10, and gases like so2 are responsible for over 95 per cent of the health damage. Delhi-based Centre for Science and Environment repeated the study by substituting the cpcb air quality data for 1991-92 by the corresponding 1995 data and found that the number of premature deaths had increased in all cities from 40,351 in 1991-92 to 51,779 in 1995 and in Delhi from 7,491 to 9,859 respectively. This means one death per hour due to air pollution in the capital.

The situation in Delhi is particularly bad because of the cocktail of pollution recorded on a daily basis, in which several pollutants exceed the air quality standards at the same time (see box: Danger signals ). "If the small particle pollution levels in California ever reached the same levels as Delhi, Californian environment authorities would have declared an emergency. All emission sources in the city would have been shut down and vehicles taken off the road," said Shankar Prasad of carb.

On the other hand, the publication of air quality data in India takes more than two-three years, making air quality monitoring a purely academic exercise. Informing the public about the quality of the air on a daily basis is a far cry. If we apply the Mexican criteria of declaring emergencies on the basis of particulate level in Delhi, the city will be closed for almost half the year (see box: Crying out loud ).

Although scientific information will always be inadequate, keeping in view the primacy of being pre-warned and exercise precaution, it is important to act on time. Martin Williams of the department of environment and transport and the regions Air and Environment Quality Division in uk writes: "Uncertainty in science should not be used as an excuse for postponing action. Where there are emerging scientific reasons for going further, it is the business of those concerned with policy to find a common ground on which policy can move on risk assessment and risk management." Time the Indian administration paid heed to this approach.

With inputs from Anumita Roychowdhury and Priti Kumar.

Particles in our body

Foul air: Aggregates of diesel (Credit: Source: Reproduced from Partic) Despite the mounting evidence on the serious health risks from particulate pollution even at relatively low concentrations, the biological mechanism by which it adversely affects humans is not understood properly.

The who estimates that about 500,000 deaths are caused per year throughout the world due to exposure to particulate pollution. Shockingly, 20 per cent of these deaths occur in India, who states that in India alone 100,000 people die due to particulate air pollution -- well above 20 per cent of the total toll (see graph: Inhaling poison ). A 1999 report published in Risk in Perspective , a journal brought out by the Harvard Center for Risk Analysis, states that even in cases where air pollution is not the direct cause of death, it would have contributed significantly to accelerate the process by which people fall ill and die from other causes.

Effect on lungs and the heart: As early as 1935, it was predicted that 68 per cent of inhaled particles that measured 0.03 micron were deposited in the pulmonary passage. The discovery was ignored at that time. Today, internationalstudies have confirmed the link between high levels of particulate air pollution and the decline in lung function or increase in respiratory ailments such as cough, shortness of breath, wheezing and asthma. Research is being conducted toprove beyond doubt the biological process by whichparticulate air pollution affects human health (see box: Pollution and mortality ).

First finding: One recent hypothesis explains that on entering the lungs, particles restrict the availability of oxygen to the lung muscles, causing ischemia, a condition that affects the cardiac rhythm (heartbeat), resulting in heart attack.

Second finding: Yet another hypothesis states that particles cause inflammation of the lungs, which in turn affects the closely linked pulmonary and cardiovascular systems. It goes without saying that if the effects on lungs and the respiratory system are experienced across a population, particulate air pollution can have substantial impacts on life expectancy (see box: The US experience ).

Third finding: Epidemiological studies in the us based on the daily time-series has established the link between specific causes that lead to death with short-term increases in air pollution. These include heart attacks, emphysema (enlargement and partial amalgamation of the air sacs of the lungs, resulting in breathlessness and wheezing) and chronic bronchitis. In these studies, death which is caused by pollution occurs to people with serious pre-existing health problems, especially the elderly.

Even if the air pollution levels do not cause death, those affected can be expected to live anywhere between a few days to a few years. However, the quality of life and health will certainly be less than that experienced by a healthy individual of the same age.

Fourth finding: According to the quarterly newsletter of the Boston-based Health Effects Institute, usa , similar health effects of exposure to particulate matter have been reported in time-series epidemiological studies (daily changes in health outcomes with corresponding alteration in pollution levels) conducted in a variety of locations in which the relative amounts of particular types of particulate matter (like pm 10, pm 2.5 and so on) are different. These results give rise to further questions: what attributes of the particulate matter mixture renders it toxic? What elements in the particulate matter adversely effects the individual?

Fifth finding: The report by Harvard researchers, entitled Valuing the Health Effects of Air Pollution , states that for each premature death due to cardio-vascular causes induced by particulate air pollution, there may be several non-fatal heart attacks. It further explains that although these non-fatal cases do not result in immediate death of the patient, they may cause permanent damage to the patients cardiovascular system and induce loss of life expectancy.

Effects on children: Apart from those suffering from heart-related problems, elderly and children are most susceptible to particulate pollution. A 1997 study in the us on the relationship between selective causes of post-neonatal infant mortality and particulate air pollution found an association between increased infant mortality rates due to particles present in the air.

According to another report published in the us -based journal Environmental Health Perspectives in June 1997, there is 40 per cent greater probability of respiratory problemsand 45 per cent greater probability of death due to respiratory causes among babies who are exposed to pm 10 concentration of about 40.1-68.8 g/cum than those exposed to lowerlevels of 11.9-28 g/cum. The report was based on a studyconducted by epa and National Center for Health Statistics during the period 1989-91. The results of the study hasserious implications for cities like Delhi, where pm 10 levels reach 820 g/cum.

Increased risk of cancer: Particulates are now treated as toxic air contaminants and a safe limit cannot be ascribed to them because the end point of the risk is cancer. The only way one can reduce the risk is by lowering the exposure as much as possible. The cancer-causing potential of particulates has been studied in detail in the case of diesel particles. Scientists have conducted toxicological and epidemiological studies to examine the cancer-causing potential of diesel particles. Based on human epidemiological data, the Scientific Review Panel of the carb points out that a chronic exposure to 1g/cum of diesel exhaust will lead to 300 additional cases of lung cancer per million people .

Diesel exhaust emissions, rich in pah s and particulate matter, causes 10 times more mutation than leaded petrol, which in turn is 10 times more mutagenic than unleaded petrol, according to Swedish tests.


Relevance to India

While countries with comparatively low particulate pollution are concerned, the Indian administration is complacent

While analysing the trend in urban air pollution worldwide, air pollution scientist Dieter Schwela of who points out that in developing countries, levels of so2, total suspended particulate matter (tspm) and pm10 are decreasing and are below the air quality guidelines set by who, while in developing countries the levels are steadily increasing.

While the West is discussing the possibility of monitoring pm1, India is not even geared to monitor pm10, let alone pm2.5. Only in Delhi the Central Pollution Control Board (cpcb) has started monitoring pm10 since March 1998 and that, too, only at one station -- Income Tax Office (ito) crossing. And the pollution levels are frightening. These have remained well above the standard throughout the year. The pm10 levels were even worse than tspm levels. In November 1998, they were more than five times above the standard, and in December, the concentration reached a high of 820 g/cum, more than eight times the standard. The data available for the first three months of 1999 show that the level of PM10 was always above the permissible limit and reached as much as five times above the standard during January and February.

Now, there is medical evidence to establish its immediate effect on public health in the capital. A recent study by J N Pande, professor of medicine at the All India Institute of Medical Sciences (aiims), New Delhi, throws up more evidence to support the link. The study, conducted over two years at the emergency room of the aiims, reveals that Delhi's polluted air is responsible for over 40 per cent of the emergency hospital admissions of patients with respiratory and heart problems.

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