The researchers have developed a novel method of using silicon nitride to enhance the efficiency of photonic elements, promising faster, more secure, and energy-efficient technologies for communication and information processing.

Beating the Blues of Air Pollution

Read time: 12 mins
5 Jun 2019
Beating the Blues of Air Pollution this World Environment Day

In India, air pollution is the leading cause of death and is responsible for 1.2 million premature deaths every year—more than the number of people killed by road accidents, smoking or malaria. Long-term exposure to polluted air is known to cause lung cancer, heart disease, stroke and diabetes. Breathing problems like asthma have surged in recent years, and about 350,000 new cases of asthma are reported among children each year in the country. It is no surprise that on average, a child born today in South Asia will lose two and a half years of its lifespan because of the impact of air pollution on health.

The 5th of June each year is observed as the World Environment Day for “encouraging worldwide awareness and action to protect our environment”. Every year, the official celebrations are organised around a theme and hosted in a different country. For 2019, the theme is ‘Air Pollution’, and the host country is China, with the main event being held in Hangzhou.

On this occasion, Research Matters caught up with three leading scientists from the country actively pursuing research on different aspects of air pollution. In an interaction organised by the Infosys Science Foundation, the three researchers, Prof. A R Ravishankara, Prof. S K Satheesh and Prof. Navakanta Bhat shared their work and thoughts on the ‘burning’ problem of air pollution.

Prof. A R Ravishankara is a Professor in the Department of Chemistry and Atmospheric Science at Colorado State University. He has worked over the past three and a half decades on the chemistry of the Earth's atmosphere related to stratospheric ozone depletion, climate change, and regional air quality. Prof. S K Satheesh is a meteorologist and Professor at the Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru. His work includes studies on how aerosols interact with the climate of a region. Prof. Navakanta Bhat, also from IISc, is a Professor at the Centre for Nano Science and Engineering (CeNSE) and works extensively on developing novel sensors for various applications, including detection of air pollutants.

Prof Sateesh and Prof Bhat were awarded the Infosys Prize in 2018 for their contributions to their respective areas, and Prof Ravishankara is a member of the jury that awards the Infosys Prize.

Greenhouse gases—fuelling climate change

Human-induced climate change is one of the defining environmental issues today. The changing global temperatures, precipitation, wind patterns and other weather phenomenon across the world have increased in recent years, resulting in floods and droughts. It is also affecting agriculture, wildlife, livelihoods, commerce and human productivity. A related culprit is global warming, where the average temperature of the planet is steadily increasing.

The Earth receives energy from the Sun, and its surface heats up. The heat is then radiated back. However, certain gases, like carbon-dioxide, known as greenhouse gases, absorb this radiation, thereby preventing it from leaving the Earth’s atmosphere. In effect, they act like a blanket. This phenomenon, in turn, causes the temperature to increase, bringing with it other damaging consequences such as rising sea levels and greater climatic variability in its wake.

In 2015, 184 countries signed up to the Paris Agreement, a landmark international agreement under the aegis of the United Nations, to combat climate change. The signatories have pledged to work towards limiting the average rise in global temperature to less than two degrees centigrade. Naively, it might appear that a change in temperature of a mere 2 degrees centigrade is not much of a problem as humans can adapt to much larger temperature changes on a daily basis. Alas, it is hardly about us!

Prof. Ravishankara, who has long been involved with the United Nations Environment Programme (UNEP), explains that we have to “focus on what the two degrees does”. This ‘small’ rise can affect both location and intensity of precipitation. “In countries like India, it would have enormous consequences as it can affect the intensity and frequency of monsoons or even effect a shift in terms of longitude,” he says, adding that it could shift the monsoon rains northwards or southwards. It is akin to how one feels when one has a fever —although the temperature change could be small, one can feel really ill.

Carbon-dioxide, the main culprit behind global warming, has always been in the atmosphere in small quantities. However, the levels of carbon-dioxide in the atmosphere today are higher than they have been at any time in the last 400,000 years, and that is the problem. Burning fossil fuels in the recent centuries has contributed massively to this increase.

“We need to do something about carbon-dioxide because it is going up,'' says a concerned Prof. Ravishankara. “People don’t appreciate the fact that even if you completely stop putting carbon-dioxide into the atmosphere, there is still a lot of it out there and it will be with us for a long time impacting our climate. The low hanging fruit is to increase fuel efficiency, particularly in vehicles, and to go for renewable energy sources”, he adds.

Although carbon-dioxide is the critical factor, it is not the only gas contributing to climate change. “There are other greenhouse gases released into the atmosphere due to various human activities, like methane and nitrous oxide”, explains Prof Ravishankara. His research on the effects of fully fluorinated gases that contain only carbon and fluorine was the impetus for including them in the Kyoto protocol—an earlier international agreement to combat climate change. “These gases, containing only carbon and fluorine, are potent greenhouse gases because they are extremely stable and live for a long time. They are man-made gases used in the silicon industry”, he points out. Another such gas is sulfur hexafluoride, which is used as insulator. “Basically, if you put these in the atmosphere, they will stay there for a long time, often tens of thousands of years,'' he warns.

Atmospheric Aerosols—tiny particles, big problems

Atmospheric aerosols are extremely tiny solid or liquid particles that are suspended in the atmosphere. These include fog, dust, haze, smoke and particulate air pollutants. Aerosols block the radiation that reaches the Earth from the Sun, resulting in lowering temperatures locally. They also affect cloud formation and monsoon winds. When it comes to climate change, some aerosols can contribute to heating, while others can cause cooling. Rather than their global impact, their local impact is of greater interest and consequence.

“Aerosols have a two-fold impact—on human health and on climate,” says Prof. S. K. Satheesh, talking about their impacts. “In India, the principal aerosol is black carbon”, he says, adding that “any kind of burning, such as agricultural burning, biomass burning, waste burning or fossil fuel burning produces black carbon”.

Besides, vehicular emission is a major culprit, he says. “Although there are increasingly stringent regulations on vehicle emissions, the number of vehicles is going up so fast, that it is outpacing any potential gains due to cleaner emissions from each vehicle. In addition, coal based thermal power plants are also a major source of black carbon,” explains Prof Satheesh.

In one of his studies, Prof. Satheesh and his group have found that aerosols have a significant impact on the Indian summer monsoon. They carried out experiments using aircrafts, finding that during the pre-monsoon season, there is a significant concentration of aerosols at a 3-4 km altitude over central and northern India. These aerosols cause intense warming, giving rise to convection currents. When the warm air rises, the moist air from southern India is forced to move northwards.

“The consequence is a change in the distribution of rain from the south to the north and north-east. We will get a lot of rain in the north, but a substantial reduction in the south,” explains Prof. Satheesh, terming it a “dangerous scenario”.

Additionally, aerosols like black carbon have a detrimental effect on health. “Asthma is growing, especially among children in bigger cities. The reason is the increase in the PM2.5 levels”, points out Prof Satheesh. PM2.5 is ultrafine particulate matter with a diameter of less than 2.5 microns, about one-thirtieth the width of a human hair. These particles can be inhaled easily, and can find their way into our respiratory systems causing a variety of respiratory ailments. “Wherever traffic density is high, asthma is also correspondingly high”, he says, on the observations.

Prof. Ravishankara and his research collaborators have found that “a lot of PM2.5 moves from one region of India to another. The Indo-Gangetic plain is the main source of these compounds which originate from open burning of dung, wood etc., transportation related from diesel cars and trucks, dust made in cities from human activities and power plants. But they find their way to other parts of the country and to neighbouring countries.” Consequently, in the absence of international treaties for PM2.5, he feels that it is essential to develop a “pan sub-continental abatement strategy.”

Monitoring air pollution—Seeing is believing?

Looking around, most of us are convinced that the air we breathe in is not clean and has hazardous pollutants. But how bad is it really? How much of pollutants do we breathe in each day? If seeing is believing, Prof. Navakanta Bhat’s research comes in handy here. Prof. Bhat and his research team have developed novel sensors, including one to monitor air pollution, using electronics and nano science.

“Unless we measure it, we cannot control it. When we talk of air quality, there are two aspects. Firstly, particulate matter. Secondly, gases like carbon-dioxide, carbon-monoxide, nitrogen-dioxide and sulphur-dioxide”, says Prof Bhat, reiterating that it is essential to better monitor air quality.

“In Bangalore, there are conventional air quality monitoring stations at the airport and in Peenya. But they are enormously expensive, costing a few million rupees each. We have developed gas sensors using semiconductors. When it comes in contact with a particular gas, its electrical resistance changes. We can determine how the resistance changes as a function of the amount of gas absorbed, and as a result we will be able to determine the concentration of the gas in the atmosphere,” explains Prof. Bhat on the novel sensor designed by his team of researchers.

These sensors are inexpensive and work well. “In a few years, we could see such devices being deployed at busy traffic junctions and various locations around the city. Eventually, it could be incorporated on smartphones which already contain lots of sensors like fingerprint sensors. This would give people real time information about atmospheric pollutants”, hopes Prof Bhat.

What Is To Be Done?

Creating awareness about the problem is the first step towards solving it, acknowledge the scientists. Explaining his efforts to make his research accessible, Prof. Satheesh says, “We prepare policy briefs in non-technical language with graphics that are sent to all relevant ministries. We focus on the health effects of black carbon and the effect on monsoons which they are likely to be concerned about. We also run awareness programmes for Members of Parliament and Legislative Assemblies of various states.”

Many of these environmental problems require collective action, often on a national level, and in many cases, even on an international level. Clearly, we can all attempt to influence these policies, in whatever ways are available to us. But, are there things we can do directly as individuals?

“Nitrous oxide is implicated in both climate change and negative health impacts. It turns out that nitrous oxide comes mainly from food production. Artificial fertilizers are the reason we can feed everyone, but their use has this unfortunate environmental impact. We can do without lots of things, but food is not one of them. But, what we can and should do is to reduce food waste,” advices Prof. Ravishankara.

There are simpler things too. “Instead of using motor vehicles, we can walk, which is also good for health. Also, using public transport and replacing petrol and diesel vehicles with electric vehicles will also help. I have noticed that people leave lights and fans on when they are not around. At my institute, I am trying to ensure that people do not do so”, remarks Prof Satheesh.

At a global level, can international treaties and policies help combat air pollution? “Since policy makers receive inputs from various quarters, it is difficult to ascertain the impact this has”, says Prof Satheesh. The path-breaking Paris Climate Change agreement could be a failure if we don’t act now, says Prof Ravishankara. “I am sceptical whether we will meet the 2 degree target, at least going by the way things are progressing right now. It is not looking hopeful unless very many countries take drastic actions. But there is no sign of that at all. On the contrary, several countries will actually increase carbon-dioxide production.”

Prof. Ravishankara also warns that besides climate change, “we need to address key issues like ozone layer depletion, acid precipitation and air quality at the same time.”

An often cited success story of countries coming together for the cause of environment is the Montreal Protocol, aimed at curtailing emissions of chloro-fluoro carbons (CFCs) that was responsible for depleting ozone in the atmosphere. Recent studies have shown that the thinning layer of ozone on the South Pole, famously referred to as the ‘ozone hole’, was getting better after steps were taken by the signatories to control the emissions of CFCs.

“Contrary to popular belief, the ozone hole is still there and makes its appearance every September-October over Antarctica”, says Prof Ravishankara. “The ozone layer is being depleted by CFCs (chlorofluorocarbons) and other ozone depleting gases. The Montreal protocol curtailed emissions of these gases, but it takes a long time for all these chemicals to go away from the atmosphere,” he opines.

In fact, the ozone layer is expected to return to its pre-1980s health only by 2075. Even that outcome will only ensue provided all countries abide by the Montreal protocol. Alarmingly, scientists have recently discovered clear indications that one of the banned substances is being released into the atmosphere. “We cannot put those substances back into the atmosphere. Just because you think you have solved an environmental problem, you cannot just forget about it. You need to constantly keep track of it,” signs off Prof Ravishankara.