(1) Air

Air Quality 101: The Basics

Air8

Without the layer of air that surrounds our planet, neither we nor any of the other forms of life that have evolved on Earth could exist. The general term for this layer of air is ‘atmosphere’, a word derived from the Greek atmos (vapour) and sphaira (ball or sphere). Of all the subsystems within the environmental system, the atmosphere has a number of unique characteristics. It is continuous around the Earth, but compared with the size of the Earth, the atmosphere is a thin shell. The part of the atmosphere we know best and live in – the troposphere – is an even thinner shell, only around 12 kilometres (7.5 miles) thick. If the Earth were the size of an apple, the atmosphere would have the thickness of the apple peel, yet this thin film of gases fulfils many essential functions. It is in the troposphere that all weather occurs; it is only here that life exists. Wind systems and rainfall patterns result from the differential heating by solar energy of the Earth’s surface and, subsequently, the atmosphere. Such weather manifestations are visible from space.

Have you ever thought about how much air you need to breathe each day? We take the air for granted, but think how long you can go without food or water compared to how long you can hold your breath. The basic biological air requirements for a person weighing around 68 kg.

Air requirements for human activity at typical ground-level pressure (100 kPa)

Activity l min−1 l hour−1

Resting 7.4 444

Doing light work 28 1680

Doing heavy work 43 2580

Based on this information, if we take a working day to comprise 7 hours of heavy work, 7 hours of light work and 10 hours of rest, we need 34 260 litres or 34.26 m3 of air per day. Taking the density of air as 1.29 kg m−3, the mass of air required comes to 44.20 kg. In comparison, we eat no more than about 1.5 kg of food each day, so our air requirement is nearly 30 times our food requirement. Similarly, we probably drink no more than about 2.5 kg of water each day. This indicates why air quality is so important; any contamination needs to be much lower in air than in food and water if we are to ensure that our total intake of potentially harmful substances does not put our health at risk. We cannot choose the air we breathe.

In our modern, technological society, we also need air to burn fuels for heating and for transport.

What is air pollution?

The United Kingdom is where the industrial revolution began, bringing with it a legacy of damage to the natural environment and public health. Resources such as water, coal and minerals were exploited, and by the middle of the nineteenth century the air and water were choked with industrial emissions. Indeed, the image of a prospering industry was of smoking chimneys. The first measures to protect the environment can also be traced back to this period. The air is obviously an important part of the environment to protect – it is essential for the survival of all higher forms of life on the planet. While seemingly vast, the atmosphere accounts for only about 1% of the diameter of the Earth. It is also continuous and so may be contaminated by activities perhaps hundreds or even thousands of miles away. We usually refer to this contamination as air pollution. The World Health Organization (WHO, 2013) has defined air pollution as: chemical, physical or biological agent that modifies the natural characteristics of the atmosphere.

There are two aspects of air pollution that are of major importance to life on Earth. Some constituents of the atmosphere may have a directly harmful effect on life forms, and other constituents may cause significant damage through changing the Earth’s radioactive balance. The spatial continuity of the atmosphere makes it nearly impossible to contemplate remediation, so pollutant releases to atmosphere must be considered with caution. Pollutants can be transported great distances, having an impact far from the emission source. A well-known example of this is the catastrophic fire and subsequent explosion at the Chernobyl Nuclear Power Plant in April 1986, in what was then the Soviet Union. This had a widespread effect across much of Europe, with pastures as far away as Wales and the Lake District – around 2300 km from the source – being contaminated due to airborne pollution.

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