What is air pollution?

by Ian Longley

Pollution is bad. The word ‘pollution’ conjures up images of something dark, something menacing, something nasty that turns up where it shouldn’t. The notion of something clean and pure being invaded by something repulsive or distasteful that spoils it, leaving it degraded, is found in traditional cultures across the world. It is implicit that pollution involves harm or risk and as such it also breeds fear. What scares us most, I think, is that it creeps up on us usually without us knowing, invading our bodies regardless of whether we deserve to be punished or are pure of heart.

Of the forms of pollution available, air pollution is one of the most insidious of all. It is frequently invisible and comes without warning, even as you sleep at night. It is, however, an equal opportunities polluter. Whereas the rich can avoid the risk of water pollution by buying bottled water, they cannot rely on buying bottled clean air. When a city is hit by an episode of bad air pollution the rich have to share the pollution with the poor.

But exactly what is it? I like to think of air pollution as any unwelcome substance that is found in the air that can cause harm to ourselves or the things we need and cherish, or that affects the air itself in ways that offend our values. We instinctively think of air pollution as toxic chemicals released into the air by industry or maybe as a by-product of transportation. This makes intuitive and scientific sense. Modern civilisation relies on various processes – controlled combustion, metalworking, manufacturing, the use of solvents, etc – that release substances into the air that were not there before the industrial revolution. Consequently our bodies, and especially our lungs, are exposed to a challenge to which they have not had time to evolve a defence for. However, other air pollutants do pre-date the industrial revolution. They include smoke from wildfires or wood fires, wind-blown dust, volcanic dust and biological material like pollen, rusts, dander, bacteria and viruses. All of these pollutants vary not only in their chemical composition, but also in their physical nature (some are gas, some liquid, some solid, or combinations of the three), their size and shape (in the case of liquid or solid ‘particles’), and so it should be no surprise that their impacts can vary enormously too.

The impacts that we are usually most concerned about relate to what happens when we breathe in polluted air. We have learned a lot about the effects of inhaling air pollution from the study of tobacco smokers, and a major global research effort over the last few decades has generated a huge scientific literature on a huge range of effects on the body and on health. A major breakthrough has been understanding how air pollution is not restricted to the lungs but can ‘translocate’ into the bloodstream, and from there to almost any body system. More recently research attention has turned to other ways in which air pollution can enter and affect the body. This includes ingestion (swallowing), absorption through the skin, and inhalation through the sinuses. Despite this, the human body is immensely complex and there is still a lot that is not known and research will almost certainly continue for decades to come.

But there are other harms that can arise from air pollution. Harmful pollution is often invisible and odourless, so that we are unaware of the risk. It follows that when air pollution does have a smell, or becomes visible, then the biological risk is added to by a psychological risk. Fear of pollution can be as serious a problem as the biological effects on the body. This fear is often triggered by odour or noise. We are more likely to think we are being polluted by traffic if we can hear it and smell it (or think we can smell it). Moreover, some research has indicated that exposure to odour, noise or almost any form of chronic stress can weaken the body’s defences and make one more vulnerable to the biological effects of air pollution. Odour is an air pollution in itself, as it can induce a range of emotions including repulsion, annoyance or artificiality. When air pollution produces a visible haze, smog, or is present as smoke or dust clouds, it can offend our sense of cleanliness inducing feelings of anxiety. Air pollution can also directly damage plants, including those grown for agriculture, and building materials. The atmospheric corrosion and soiling of treasured buildings, monuments and artwork is a form of slow cultural pollution that can sadden our hearts and is very hard to reverse.

In New Zealand, there are three dominating forms of air pollution. The first is pollution in a ‘technical’ sense, in that we observe it as a common constituent of our air, especially near the coast, and that is sea salt. This is due to our island geography. Crashing surf and collapsing wind-whipped whitecaps toss droplets of sea water into the air which evaporate leave tiny crystals of salt suspended in the air. Whether it causes any harm is not clear. The second major form of air pollution in this country is exhaust from road vehicles, ships and other diesel engines. Some of this comes from industries and major businesses, but clearly some comes from you and I driving our cars. When we start to think about what can be done about air pollution, and who’s to blame, our views often start to change. This is because it forces us to recognise that most air pollution is a by-product of things we like – mobility, jobs, an economy. This is even more so for the third major form of air pollution in New Zealand – smoke from burning wood or coal for home heating. Here it is entirely private individuals and households who are ‘to blame’. But blame is, of course, far too harsh a word. People are only trying to keep themselves warm in a way they can afford. And, in many ways, wood is a sustainable, renewable resource which still works even when the electricity is out. This conundrum is a major scientific and political challenge for this country.

Recognising air pollution is not so straightforward. Our fears often fail to match the reality. But what we can scientifically measure isn’t always what matters most. We intuitively know what pollution is, but out intuition can also mislead us. We know a lot about what pollution does to us, but there is still much to learn. And controlling air pollution means coming to terms with our role in creating that pollution and acknowledging that we are naturally reluctant to curtail activities that give us benefit because they are also polluting.