The long-term impact of scientific-technological developments on twentieth-century life was enormous. These developments were crucial, for example, in greatly increasing people's life expectancy (see below) and the global population from 1.6 billion in 1900 to 6 billion in 1999, an increase that would have major environmental consequences (see Chapter 6).

The line between technology and science, especially applied sciences such as aeronautics, agronomy, electronics, engineering, medicine, and metallurgy, is sometimes difficult to discern. For understanding twentieth-century history, however, what is most essential is to comprehend the areas of human life that were most affected by their combined impact. In general, science deals more with principles and theories, whereas technology is concerned with techniques, tools, instruments, machines, and other products that help humans to accomplish various tasks. Science itself was often poorly understood and took on significance for most people only when it led to technological developments like advancements in medical treatment or sending men to the moon. In the early twentieth century physicists like Max Planck, Albert Einstein, Niels Bohr, Ernest Rutherford, James Chadwick, Werner Heisenberg, Hans Bethe, and Enrico Fermi participated in a golden age for their science. And people heard of some of their new terms such as Quantum Mechanics, the Theory of Relativity, and the Uncertainty Principal, but few non-scientists really understood their meaning.

Ozone is the triatomic form of oxygen. It is a colourless gas that acts as a highly reactive oxidising agent. It is the primary oxidising irritant in photochemical smog. On the other hand, ozone is used to deodorise air, purify water and treat industrial wastes. Ozone is a strong absorber of ultraviolet radiation. Ozone can be both good and bad: bad to breathe near the surface in the troposphere, but good to shield from ultraviolet (uv) radiation in the stratosphere.

One of the most important properties of ozone is its ability to absorb ultraviolet radiation (discovered by Hartley 1880). The earth is surrounded by a thin layer of ozone that is sufficient to screen us from the ultraviolet radiation from the sun that would otherwise reach the surface, where it would be capable of breaking bonds in biologically important compounds such as DNA (e.g. Björn 2007). The thin layer of ozone in the stratosphere is only about one part in a million of the total molecules that make up our atmosphere. If the entire layer were reduced to surface pressure, it would be only 3 millimetres in thickness. Figure 5.1shows how the air temperature and ozone concentration changes within the troposphere and the stratosphere.

Temperature decreases throughout the region called the troposphere. Temperature is then constant or slowly increasing, forming a permanent inversion layer called the stratosphere.

Wars, assassinations, atrocities—these words appeared often in the twentieth century. No earlier century had witnessed as much killing. Population increases provided more people to kill; technological developments provided more efficient means to do so; and expanding media coverage informed more people about such killings and horrors as the century proceeded.

History books, however, are better at providing mind-numbing statistics regarding all this killing than they are at conveying much feeling for the millions of individual tragedies caused by it. The British novelist Ian McEwan hinted at this problem when he wrote about one of his characters:

Some feeling for all these tragedies is also sometimes conveyed by firsthand accounts. A few early ones are provided here, and readers can only attempt to imagine some of the other millions of tragedies which lie behind the gruesome statistics of the remainder of the century.

Imperialism

Imperialism has existed for many centuries and is defined in different ways. Some scholars have related it directly to their definition of empire. For our consideration here, however, which lies mainly with the twentieth century, it seems best to define it as a country's extension of rule or authority by force or the threat of its use over a foreign territory. Such a simple definition sidesteps the very complex arguments among scholars about formal and informal empires and what constitutes an empire. Such debates need not bog us down here.

The imperialism of the late nineteenth and early twentieth centuries had many unique features. The desire for new markets to absorb the increasing capitalist productive capacity and to help overcome the global depression of 1873 to 1896, along with technological advances in shipping, communications, and military capacities, stimulated a new outburst of imperialism. British Prime Minister Lord Salisbury said in 1895, “We must be prepared to take the requisite measures to open new markets for ourselves among the half-civilized or uncivilized nations of the globe.” In 1898, the year of the U.S. annexation of Hawaii and of the Spanish–American War, political orator and soon-to-be senator from Indiana, Albert Beveridge, expressed a similar sentiment:

Closely connected to the twentieth century's changes in science, technology, economics, and politics have been those to the environment. One historian wrote that “the human race, without intending anything of the sort, has undertaken a gigantic uncontrolled experiment on the earth. In time, I think, this will appear as the most important aspect of twentieth-century history, more so than World War II, the communist enterprise, the rise of mass literacy, the spread of democracy, or the growing emancipation of women.”

In his book The Coming Anarchy (2000), Robert Kaplan declared that “it is time to understand ‘the environment’ for what it is: the national-security issue of the early twenty-first century. The political and strategic impact of surging populations, spreading disease, deforestation and soil erosion, water depletion, air pollution, and, possibly, rising sea levels in critical, overcrowded regions like the Nile Delta and Bangladesh—developments that will prompt mass migrations and, in turn, incite group conflicts—will be the core foreignpolicy challenge from which most others will ultimately emanate.”

Two major and interconnected factors, both fuelled by scientific and technological developments, were responsible for the twentieth century's unprecedented environmental changes and their importance by century's end: population growth and economic activities, especially industrialization and increased consumption. The explosion of twentieth century consumption (see Chapter 3) not only placed increasing demands on scare resources to produce more goods, but also increased pollution in the process of producing and disposing of worn out or obsolescent products.

We are living in an increasingly shrinking world. Instant communication and the internet have seemingly dissolved time, space and cultural boundaries. The international movement of peoples has reached levels previously unheard of. Globalization has become a catchphrase for our times.

The atmospheric sciences have partly led and partly responded to this process. The extent of continental, hemispheric – and even global – transport of air pollution has become an issue of increasing scientific and policy concern; and nothing emphasises the fragile unity of the planet more graphically than the increasing evidence of climate change – and the portentous implications that emerge as we contemplate the possible consequences of the interaction of air pollution and climate change.

Yet appearances can be deceptive, and are only part of the story. Even for scientists, the ‘Big Picture’ is never easy, and, for the most part, the pressures of professional life mean that we must concentrate on the particular and limit ourselves to our own field. We are able only from time to time to look outside our own boxes, and this task paradoxically becomes more difficult as the totality of knowledge in our separate specialties increases.

For the ordinary citizen, with no specialist training in the atmospheric sciences, there is a similar problem. The unity of the atmosphere, and of the atmospheric sciences, is less easy to grasp than the variety of seemingly separate problems, such as climate change, ozone depletion, urban pollution, and industrial and vehicle emissions, which at different times rightly command separate and urgent attention.

Atmospheric pollution affects us all. It affects our health and our environment. It is our activities and actions, however, which are resulting in the continual pollution of the atmosphere. For example, road transport has emerged as one of the most important sources of air pollution, particularly in urbanised areas such as mega-cities. Although emissions from other sources, such as industrial and domestic have reduced in developed countries, they still make a significant contribution to the overall pollution burden of the atmosphere in many less developed regions.

It is not only the directly emitted pollutants that can be hazardous to our health and the environment. Pollutants can also react with each other in the presence of sunlight to produce harmful photochemical smog, which affects many cities around the world. Once released into the atmosphere, pollutants can be dispersed into buildings and along streets as well as affect whole city areas. As a result of meteorological processes air pollution can also be transported across continents and, depending on the particular chemical species, remain in the global atmosphere for long periods of time. Pollution emitted locally by cars, industrial chimneys or forest fires, therefore, can have an impact on regional and global scales. On the other hand, pollutants such as aerosols and carbon dioxide, which influence the global radiation balance of the atmosphere, can lead to changes in the natural climate of the world with direct impacts on urban and local scales.

This introduction brings together the separate, but interlinked, themes of the chapters. Some of the key concepts of atmospheric pollution are explained to help those readers who are not familiar with the subject area but have a science background. This section also explains the overall structure of the Atlas and the approach adopted by the contributors. A list of useful reading material is provided at the end of the Atlas for those who are interested in an in-depth treatment of atmospheric science and pollution.

The Earth's Atmosphere

Radiation Balance of the Atmosphere

The overall atmospheric dynamics and the climate system are driven by the energy from the sun. Much of the incoming solar radiation is transmitted through the atmosphere and absorbed by the earth's surface (see Figure I.1). Some of this short-wave radiation is reflected by ground surfaces such as snow and deserts, and by clouds. About 30 per cent of the solar radiation incident on the earth is reflected back into space by clouds, the atmosphere and the earth's surface (Kiehl and Trenberth 1997). Approximately 20 per cent of the incident radiation is absorbed by the atmosphere, and the remaining proportion (about 50 per cent) warms the earth's surface (land and the oceans).

The proportion of incoming radiation that is reflected back by a surface depends on its reflectivity, and is termed ‘albedo’. For example, albedo of fresh snow is typically 0.8 and that of the earth and the atmosphere, 0.3.

The scientific and technological developments of the twentieth century occurred within economic or social systems such as capitalism and communism. Of the two, capitalism generated by far the most such developments. As the economist Joseph Schumpeter noted, in its search for new products, new consumers, and new markets, capitalism constantly revolutionized “the economic structure from within, incessantly destroying the old one, incessantly creating a new one.” He even wrote that “this process of Creative Destruction is the essential fact about capitalism.” The system itself can be defined as an economic one in which means of production such as land, labor, and machinery are privately owned by individuals and businesses that produce and exchange goods and services primarily to earn a profit—in contrast, under communism the government usually owned the means of production. By 1900, countries with capitalist economies dominated the globe. Among them the United States, Germany, Great Britain, and France were the leading powers, and to a lesser extent Austria- Hungary and Russia, in both of which capitalism was at a less advanced stage of development. Although socialism/communism was advocated by the German-born Karl Marx (1818–83), no communist party was able to come to power until the communist revolution of 1917 in Russia.

Although Marx recognized the tremendous productive capability of capitalism, he also believed that it was flawed by “growing inequalities, bitter class conflict, worsening cycles of economic expansion and recession, [and] competitive and individualistic values.”