Kolkata is about polluted city

What pollutes the air?

A thick cloud of haze hangs close to the floor. Such a gray veil of fog can often be seen, especially in large cities and metropolitan areas. Here the air quality suffers from the fact that a lot of dust particles are floating around. Because they are too small to be seen with the naked eye, these suspended particles are also known as particulate matter. In addition to fine dust, there are also toxic gases such as carbon monoxide or sulfur dioxide, which float in the lower atmosphere and pollute the air.

A large part of these exhaust gases are produced when crude oil, coal and other substances are burned. Cars, power plants, waste incinerators and residential heating systems blow loads of dirt into the air. In addition, there is dust that is blown up - from streets, but also from factory farming, for example. The “exhaust gases” from the livestock also contribute to the fact that the air is getting worse and worse. But it is not always humans who pollute the air: volcanic eruptions can also contribute to higher levels of fine dust in the atmosphere.

The more pollutants there are in the air, the worse it is for our health: the respiratory tract can become ill, and the circulatory system and brain are damaged. Not only humans and animals suffer from the polluted air, plants are also damaged: If too much carbon dioxide and sulfur oxide are suspended in the air, acid (carbonic and sulfuric acid) forms in connection with water. The result is what is known as “acid rain”, which makes the soil acidic. Plants growing on such soil become withered and die. We are talking about "forest dieback". This can also happen far away from where the exhaust gases get into the air, because the wind carries the acid rain clouds away for hundreds of kilometers.

Air pollution is particularly bad in metropolises in India, Pakistan and Iran or in Mexico City. In Germany there are regulations on how heavily the air can be polluted. But here, too, the values ​​are not always adhered to and car traffic continues to increase.

In order to keep pollutants in the air low, it is therefore particularly important that enough forests and parks clean the air. Because trees, like all green plants, absorb carbon dioxide from the air and produce the oxygen that is essential for us. “Green lungs” in large cities, ie green spaces and forests close to cities, are therefore particularly important for our health. And those who often get on their bikes instead of driving the car also help to keep the air clean.


Whether in Lagos, Tehran or Calcutta - the population growth is enormous in many cities and metropolitan areas. Worldwide there are currently around 20 cities with over 10 million people, so-called mega-cities. It's not just the population that is increasing here. As it grows, so do the environmental problems. Air pollution is particularly bad in the growing cities of Asia.

Millions of vehicles throng the streets, tons of exhaust gases are blown into the air. Soot, heavy metals and toxic gases accumulate in the atmosphere. Pollutants from industrial plants, households and private waste incineration are also a burden. A thick haze hangs over many metropolises such as Mexico City, Los Angeles or Beijing. This not only affects the clear view, it is also extremely harmful to health. Diseases of the respiratory tract, the skin, the cardiovascular system, the immune system and cancer can be the result. According to the World Health Organization, many cities in Asia are particularly polluted by particulate matter. One of them is Dhaka, the capital of Bangladesh. In this metropolitan area alone, an estimated 15,000 people die prematurely every year due to air pollution. According to the WHO, there are around two million worldwide.

Air quality could be improved if pollutant emissions were regulated and controlled by law. These measures are already showing success in Los Angeles and Mexico City. The situation is more difficult in the rapidly growing metropolises of developing countries. Here it is primarily primitive cooking areas that pollute the air. The thick smoke from wood and coal fires makes the airways sick. Millions of households should therefore be equipped with clean stoves by 2020.

The dirtiest cities in the world

A study by the World Health Organization (WHO) measured the particulate matter levels in large cities around the world. The metropolises of Asia in particular are heavily polluted, especially in Iran, Pakistan and India. The sad leader in air pollution was the city of Ahwaz in Iran.

1st place: Ahwaz, Iran

2nd place: Ulaanbaatar, Mongolia

3rd place: Sanandaj, Iran

4th place: Ludhiana, India

5th place: Quetta, Pakistan

6th place: Kermanshah, Iran

7th place: Peshawar, Pakistan

8th place: Gaborona, Botswana

9th place: Yasouj, Iran

10th place: Kanpur, India


It crumbles, splinters and weathered: the ravages of time are gnawing at Cologne Cathedral. Acid rain has already eroded the famous building. Air pollution laws have been reducing pollution for a number of years. But pigeon droppings, exhaust fumes and the weather continue to affect the old walls and never let the craftsmen of the cathedral builder become unemployed.

The foundation stone of Cologne Cathedral was laid on August 15, 1248. Since then, around fifty different rocks have been set in the Rhenish sand here. The builders only built many of them on a trial basis; not every stone could withstand the weather. In addition, the rock had to come from close by, as transport was incredibly expensive in the Middle Ages. As a result, the cathedral consists mainly of trachyte, shell limestone, sandstone and basalt. The calcareous sandstones and shell limestone are particularly susceptible to weathering and environmental influences. These are already badly pitted. In order to save the sensitive shell limestone from weathering, various protective coatings were tried out. That should at least slow down the crumbling. In contrast, the trachyte from the Drachenfels has held up well. The basalt rocks are also weatherproof and in good condition to this day.

Despite all efforts, components have to be replaced again and again. Every year 15 to 20 cubic meters of natural stone are used to preserve the famous church building. Even if the Cologne Cathedral was already built in 1880: The stonemasons of the cathedral building have their hands full to this day!

Stone intolerance

The Cologne Cathedral evidently weathers more than other comparable buildings. Conservationists now have a guess as to why that is so: The cathedral is built from many different types of stone. And not all rocks get along with each other. For example, the damage is particularly severe where trachyte from Drachenfels meets sandstone from Obernkirchen. A research group is now to find out whether and why some rocks actually damage each other and which of them can get along well with each other.


Global carbon dioxide emissions have never been as high as they are today. In 2010, it even rose more sharply than ever before. This has now been announced by the US Department of Energy. The numbers exceed even worst fears.

For years, experts have warned of the speed of global warming. Apparently without success: The proportion of the climate-damaging gas carbon dioxide in the air is increasing rapidly. In the industrialized countries in particular, it gushes continuously from chimneys and exhaust pipes. The new numbers are frightening: In total, the world emitted over 33,500 million tons of carbon dioxide in 2010. That is 1,900 million tons more than in the previous year, an increase of six percent!

According to the US study, China and India are primarily responsible for the increase in horror. The two countries are on a growth path economically. They get their energy primarily from coal-fired power plants - and thus produce a lot of CO2. Overall, China is the record holder for greenhouse gas emissions, followed by the USA, Russia and India.

The policy for global climate protection has so far failed completely. China and the US refuse to sell their CO2- Reduce emissions. Russia, Canada and Japan also no longer want to comply with guidelines if the main polluters are reluctant to comply with international limit values. Bad for the climate, as the new study clearly confirms on the basis of the figures.

The Keeling curve

The first CO2-Measuring station in the world was opened far away from car exhaust fumes and factories: In 1958, the American climate researcher David Keeling began to regularly measure the carbon dioxide content of the air on the Mauna Loa volcano on the island of Hawaii. This place was chosen deliberately. Because neither chimneys nor forests influenced the result, an average value of the trace gas in the air could be measured here. A second station in Antarctica also met these conditions. After two years, Keeling presented his results to the world: The level of carbon dioxide in the air rose! In the following years, Keeling continued to fight for regular CO2-Measurements of the atmosphere. With success: The result is the so-called Keeling curve, a collection of data that to this day records the carbon dioxide content of the air and the significant increase in CO2 documented.

A shell made of gas

Seen from space, it appears like a fine bluish veil that surrounds the earth: the atmosphere. It is the envelope of air that surrounds our planet. Compared to the diameter of the earth, this shell is quite thin: if the earth were the size of an apple, the atmosphere would be about the thickness of its shell.

Without the atmosphere there would be no life on this planet, because plants, animals and humans need air to breathe. It protects us from the cold and from harmful radiation from space. It also lets meteorites burn up before they can hit the surface of the earth. This atmosphere is vital to us - but what is it actually made of?

The atmosphere is a mix of different gases. A large part of this gas mixture is nitrogen: At 78 percent, that's almost four fifths of the entire atmosphere. Only 21 percent consists of oxygen, which we need to breathe. The remaining one percent is made up of various trace gases - gases that only occur in traces in the atmosphere.These trace gases include methane, nitrogen oxides and, above all, carbon dioxide, or CO for short2 called. Although the CO2-Proportion is quite low, this trace gas has a tremendous impact on our earth's climate. This can be seen in the greenhouse effect, which is heating up our planet.

The fact that the earth has an atmosphere at all is due to gravity. It holds the gas molecules on earth and prevents them from simply flying out into space. In fact, the air becomes thinner and thinner with increasing altitude and thus decreasing gravity. Even at 2000 meters above sea level, this can become uncomfortable for people: He suffers from altitude sickness with shortness of breath, headaches and nausea. Extreme mountaineers who want to climb high peaks like the 8000m high in the Himalayas therefore usually take artificial oxygen with them on their tour.

The oxygen cycle

The air we breathe contains about a fifth of oxygen. This gas is invisible, has no smell and no taste - but it is vital to us. Because we need oxygen in order to gain energy from our metabolism. Without this gas, neither humans nor most animals can survive.

Almost all of the oxygen in the air is made by plants through photosynthesis. During this process, the plant uses sunlight to create important nutrients from carbon dioxide and water. Oxygen is also produced as a by-product of photosynthesis.

The oxygen that the plant does not need is released into its environment. For example, a large beech tree produces about as much oxygen in one hour as 50 people need to breathe in the same time. Humans and animals breathe in this oxygen, use it up and breathe out carbon dioxide. Plants absorb this carbon dioxide during photosynthesis while at the same time generating new oxygen. A cycle is created between plants, people and animals.

In the course of the earth's history, much more oxygen has been released than living things have used to breathe. In this way, more and more oxygen was released into the atmosphere. The ozone layer, which protects us from dangerous UV radiation, could form high up in the stratosphere from the increasing proportion of oxygen.

Since people have been burning more and more oil, natural gas and coal, this natural oxygen cycle has been severely disrupted: burning consumes oxygen and at the same time carbon dioxide is also emitted. For this reason, the amount of carbon dioxide in the air has risen sharply over the past 250 years. The rise in this trace gas is the main cause of the man-made greenhouse effect and thus also of the warming of the atmosphere.