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For humans, and other animals, the most important atmospheric gas is oxygen. It makes up less than one-quarter of the air that we breathe (21 percent), but without it we die. It is found in breathable quantities in a layer less than 10 kilometres deep, and is most concentrated at ground level, becoming progressively thinner as altitude increases. Mountain climbers know just how thin it can get. The atmosphere at the summit of Mount Everest, Earth's highest mountain at 8,848 metres (29,022 feet), does not contain enough oxygen to sustain life.

Oxygen, of course, is not all that we breathe. With each lungful of air, we take in many other gases and small particles. The unwelcome gases and particulate matter in the air are generally most concentrated in the towns and cities where cars, factories, and houses constantly burn materials that give off smoke and fumes. Some of these are merely irritating, but others can be harmful to health.

With the exception of some nuisance odours, and agricultural spray drift, New Zealanders' air quality concerns have generally been limited to the few cities where wintertime smoke and fumes cause visible pollution problems. Today, however, awareness is growing that air pollution does not have to be visible to cause problems, and that apparently moderate levels of air pollution can cause serious problems for some people, particularly those with asthma, emphysema, or chest infections.

Figure 6.1: Heavy metal air pollution (copper) from ancient times to today

Emissions of heavy metal air pollution (copper) have increased from ancient times to today. Emissions of copper peaked during the rise and fall of the Roman Empire and the Sung Dynasty of China, although emissions remained below 100 tonnes per year. Since the beginning of the industrial age, emissions have increased dramatically and are now over 700 tonnes per year.

Source: Hong et al. (1996)

Smoke has shadowed human society since the first fires were lit tens, perhaps hundreds, of thousands of years ago. Evidence of prehistoric air pollution is found on the walls of European caves where small amounts of trace heavy metals escaped from firewood over long periods of time (Nriagu, 1996). Air pollution probably intensified with the development of towns and cities in the Middle East, northern India, and China about 10,000 years ago. The concentrations of people, domestic animals, and cooking fires in small areas would have created an ambient air quality which combined wood smoke with the odours of rotting rubbish, tanning hides, and waste from both humans and animals.

Some time later, metal smelting would have added to the mix-though the early smiths tended to live apart from the main community to protect their magical trade secrets (a tradition which lingers on in Europe's gypsies and tinkers). Metal smelting was probably discovered by accident when implements made of hammered copper, or ores containing copper, lead, and other metals, found their way into high temperature pottery kilns. This happened separately in southern Europe and China about 6,000 years ago. It took several thousand years for smelting to become widespread, and it was not until the era of the Greek and Roman civilisations about 1,700 years ago (500 b.c. to a.d. 300) that large-scale air pollution resulted (Hong et al., 1994, 1996).

The widespread use of lead in ancient Rome probably caused a considerable amount of lead poisoning (Nriagu, 1983). The impact of this on Roman society is a matter of speculation, but its scale is not. The evidence of extensive lead and copper pollution has been faithfully preserved in polar ice caps, bogs and aquatic sediments. Modern studies indicate that for some 800 years, from roughly 500 b.c. to a.d. 300, lead concentrations in the air appear to have been up to four times higher than the natural background level while copper levels were a dramatic 400 times higher.

After the fall of Rome, lead pollution disappeared for some 500 years, causing the air to lighten somewhat during the otherwise unenlightened Dark Ages. Copper levels also declined significantly but rose to another peak some centuries later when China's Sung Dynasty began extensive copper and tin smelting to produce bronze (see Figure 6.1).

It has been estimated that the total amount of copper dust deposited in the Northern Hemisphere during the 800-year flowering of Greco-Roman civilisation was about ten times greater than that deposited within the last 200 years by industrial society (Hong et al., 1996). However, the reverse is the case with lead. In just two centuries, modern society has emitted ten times more lead than the ancient civilisations could deposit in eight centuries (Hong et al., 1994). The main reason is the widespread use of leaded petrol in motor cars for most of this century.

Even an area as pristine, and as far away from the industrial North as Antarctica, has not escaped the global lead pollution of modern times. Recent analyses of Antarctic ice have found that snow deposited in the 1920s contains lead levels five times higher than natural background levels, making it slightly more polluted than the Arctic snow deposited in the time of ancient Rome (Nriagu, 1996). More recent Antarctic snow has even higher levels.

Air pollution in New Zealand began long before our arrival here. Volcanic eruptions have occasionally formed clouds of ash and smoke that proved lethal to plants and animals. Human-induced air pollution probably began with the extensive Māori forest fires which were lit repeatedly over several centuries and are still dimly recalled in the stories of Tamatea (Orbell, 1985). But vast as these smoke clouds would have been, they were episodic, not persistent. Four centuries later, when European farmers arrived to clear more forest and scrub for pasture, large fires again clouded the air and charred the hillsides, but they too were ephemeral.

It was in some of the newly-established colonial towns and cities that air pollution became a more persistent problem. Aside from chimney smoke, the towns also generated other air problems, such as the odours of rotting garbage, factory wastes, horse dung, and human sewage. These problems were probably worst in Christchurch where the swampy terrain and the frequent air inversions contributed to their intensity. Strident protests eventually led the city fathers to install a sewerage system, but, except for some factory emissions, nothing was done about the smoke and most people seemed content to put up with it.

The lack of alternatives to the open fire probably accounted for this general air of acceptance, perhaps aided by memories of far worse conditions in the big cities back home. As early as 1661, for example, before the Industrial Revolution had even begun to gather steam, one writer, John Evelyn, described the city of London as more like:

the face of Mount Aetna, the Court of Vulcan ... than an Assembly of Rational Creatures and the Imperial Seat of our incomparable Monarch ... For there is under Heaven such Coughing and Snuffing to be heard, as in London churches and Assemblies of People, where the Barking and the Spitting is uncessant and most importunate ... It is this horrid Smoake which obscures our Churches, and makes our Palaces look old, which fouls our Clothes and corrupts the Waters, so as the very Rain, and refreshing Dews which fall in the several Seasons, precipitate this impure vapour, which, with its black and tenacious quality, spots and contaminates whatever is exposed to it. (Quoted in Ponting, 1991).

By the time cities were being established in New Zealand, London's infamous smogs were killing people-a situation which continued to worsen until the terrible smog of December 1952 when over 4,000 people died (Ministry of Health, 1954). Compared to this, Christchurch's problems must have seemed mild. Nevertheless, occasional efforts were made to measure the city's air pollution (Gray, 1910). From 1884 to 1888 and again from 1907 to 1909 the dissolved solids in Christchurch's rainwater were measured and were found to be about 50 milligrams per square metre (mg/m2) per day, a level not too much lower than the 70 mg/m2 recorded many years later in the 1970s (Pullen, 1977).

By the 1930s, an organisation called the Christchurch Sunlight League began agitating for cleaner air, a cause taken up in later decades by the Clean Air Society. These Christchurch-centred campaigns eventually led to the estab-lishment of the Clean Air Act 1972, which contained measures for reducing pollution pressures in known trouble spots. That Act has now been superseded by the Resource Management Act 1991 which requires local communities, through their regional councils, to sustain the physical and natural environment, and to monitor it as necessary.

As councils attempt to meet their air management obligations, attention has been drawn to the general lack of information on air quality, outside of a few city centres, and has stimulated a rush of activity to improve the situation. The fruits of this activity will become apparent in the years ahead. In the meantime, using existing information it is still possible to derive a general picture of the state of our air, in the main centres at least, and of the current pressures affecting it.

This chapter reviews what is known of New Zealand's air quality and what has been done to remedy perceived problems. It begins by describing the general characteristics of the air over New Zealand and the pressures which human activity can put on air quality. It then assesses the state of our air, based on existing data, and summarises the responses which the community has made to address air quality problems.