Apart from volcanic eruptions, such as the recent emissions from Mount Ruapehu, there are few natural pressures on air quality. Although natural forces, such as wind and temperature inversions can influence the dispersion or concentration of air pollutants, the source of those pollutants is nearly always human activity.
Motor vehicles are responsible for air pollution in heavily used traffic corridors and are secondary contributors to winter-time ambient pollution which is primarily caused by domestic fires and is enhanced, in Christchurch, by the temperature inversion layer which prevents pollutants from dispersing (see Box 6.1). New Zealand, along with Australia, Japan, North America, and the countries of northwest Europe, has one of the highest vehicle ownership rates in the world. We have 46 cars for every 100 people, approximately one for every two persons (Statistics New Zealand, 1996). When trucks and other vehicles are included, our vehicle ownership rises to 69 vehicles per 100 people. This compares to a world average of 11 vehicles per 100 people, and continental averages of 2 per 100 in Africa, 3 per 100 in South America, 9 per 100 in the former Soviet Union, and 33 per 100 in Europe, 50 per 100 in Canada, and 100 per 100 in the United States (World Resources Institute, 1994). The number of licensed vehicles in New Zealand has grown at more than twice the rate of the human population since 1972.
While human numbers have increased by 18 percent, car numbers have gone up by 46 percent. The number of licensed vehicles peaked in 1986 at just over 2.4 million, then dipped slightly following the 1987 economic crash. By 1995, they had risen to a new peak of just under 2.5 million (see Figure 6.3).
The number of privately owned motor cars has increased from around 1,250,000 in 1980 to around 1,600,000 in 1995. When motor bikes, trucks, service vans, utilities and other types of motor vehicle are included, the numbers are around 2,200,000 in 1980 and 2,500,000 in 1995. In both cases there was a dip in 1987/88, with numbers coming close to 1980 levels.
Source: Statistics New Zealand, 1996
The trend in vehicle numbers is reflected in the increasing percentage of workers who drive to work and the falling numbers taking public transport. This information is gathered by the Census every five years. In 1971, 44 percent of full-time workers drove to work. By 1986 that figure had risen to 57 percent, and in 1991 it stood at 65 percent. (Department of Statistics, 1990; Statistics New Zealand, 1993). (The 1996 Census figures were not available at the time of writing.)
Conversely, the percentage taking public transport has plummeted from 14 percent in 1971 to 10 percent in 1986 and 5 percent in 1991. The percentage walking to work also declined from 11 percent in 1971 to 7 percent in 1986 and 1991. Those taking bicycles remained at 5-6 percent between 1986 and 1991.
New Zealand has no laws requiring vehicles to be fitted with pollution control devices or to meet emission standards. The only laws targeting air pollution from motor vehicles are the Petroleum Products Specifications Regulations 1995, issued pursuant to the Ministry of Energy Abolition Act 1989, which ban the sale of leaded petrol (see Box 6.7) and Traffic Regulation No 28, issued pursuant to the Transport Act 1962, which makes it an offence to emit smoke from a vehicle to such an extent that it obstructs the visibility of other drivers.
In many of the world's largest cities, emissions from motor vehicles are a significant source of air pollutants. In New Zealand cities, motor vehicles seem to play a secondary role to domestic fires but they can cause or contribute to pollution incidents, particularly in busy traffic corridors when wind speeds are low and traffic density exceeds 1,500 cars per hour (see Figure 6.9). The role of vehicles varies according to the pollutant. In Christchurch winters, for example, motor vehicles contribute roughly 50 percent to high carbon monoxide levels, but only about 4 percent to suspended particulate pollution.
All motor vehicles pollute to some degree, but the worst offenders are vehicles that have been poorly maintained, tampered with, or heavily used. In fact, in the United States, about half of all vehicle emissions come from just 10 percent of vehicles-namely, those whose engines are most poorly tuned (Calvert et al., 1993; Beaton et al., 1995). Until recently, lead was the most notorious air pollutant emitted by motor vehicles. Its residues were detectable even on country roadsides (Collins, 1988). With leaded petrol no longer sold in New Zealand, lead emissions are no longer a problem (see Box 6.7). Dioxin emissions from halogenated lead-scavengers are also likely to have declined. There is no evidence that other emissions have fallen, and, with the growth in New Zealand's vehicle fleet, it is likely that nonlead emissions have increased.
Emissions of concern to health researchers include: carbon monoxide (which can cause death from respiratory failure); dioxins (which have been linked to cancers); nitrogen oxides (possibly associated with asthma); fine particulate matter (linked to respiratory and cardiac deaths); 1,3-butadiene (linked to cancer in laboratory animals); and benzene (linked to leukaemia). Although the main source of exposure to benzene is tobacco smoke, a 1995 study estimated that benzene emissions from vehicles would go up slightly following the introduction of unleaded Super 96 octane petrol (M. Bates, 1996).
Petrol is not the sole cause of pollution from vehicle exhausts. Diesel fumes also emit high levels of fine particulate matter and cancer-causing chemicals (Bown, 1994b). Since 1990, diesel-powered vehicles have increased, accounting for 75 percent of new commercial vehicle registrations and 11 percent of new cars registered (McChesney, 1996). Even electric cars may not be as clean as they appear. According to one controversial estimate, if they replaced the petrol fleet in the United States, the smelting and recycling of lead for their batteries would cause an overall rise in lead emissions - though this view is contested (Lave et al., 1995a, 1995b; Allen, 1995; Stempel and Ovshinsky, 1995; Gellings and Peck, 1995; Gaines and Wang, 1995; Hwang, 1995; Rubenstein and Austin, 1995; Socolow, 1995; Sperling, 1995).
At present, petrol vehicles are responsible for 84 percent of the kilometres travelled in New Zealand (Kuschel, 1996). Of the more than 40,000 vehicles that went through the Canterbury Regional Council's Emission Testing Programme in Christchurch from 1993 to 1995, more than 17,000 (41 percent) were so poorly tuned that they failed to meet the programme's emission guidelines (Ayrey, 1996).
Many countries have combated vehicle emissions by imposing design rules on vehicles (engine controls and catalytic converters) and programmes of inspection and maintenance of vehicle emissions. Catalytic converters are devices that are fitted to the exhaust of a motor vehicle. They use chemical catalysts to convert some pollutants, such as carbon monoxide and nitrogen oxides, into less toxic forms, such as carbon dioxide, nitrogen and water. Over the life of a car, a catalytic converter can reduce emissions of carbon monoxide and volatile organic compounds (VOCs) by about 85 percent, and nitrogen oxides by about 60 percent. Catalytic converters have been the most important tool in controlling vehicle emissions in Japan and the United States through the 1980s (Calvert et al., 1993). However, they are only a partial answer. They can only be fitted to more modern petrol-driven cars, they cannot reduce particulate matter (PM10) and they actually increase the output of carbon dioxide (Kuschel, 1996). It is becoming clear that behaviour change, public transport systems and strategic urban planning have as great a role to play as technical solutions.
Home heating is the major cause of ambient urban air pollution because of the emissions from burning solid fuels (i.e. coal and wood). Both these fuels emit a range of contaminants. While coal emits twice as much particulate matter, wood emits twice as much as carbon monoxide. In absolute terms, though, most emissions come from wood fires as these are much more common than coal fires. Nationally, the number of homes with open fires has been declining, so that now only one-quarter of homes have them. Meanwhile, the proportion of homes with slow-combustion fires (e.g. woodburners) has been increasing (see Figure 6.4). This trend is not uniform, with wide variations from place to place.
A recent study of 14 Christchurch suburbs found that the percentage of homes using coal or wood fires ranged from 17 percent in one suburb to 57 percent in another (Kuschel and Foster, 1996). The suburb with the highest household air emissions was the one with the greatest number of open fires. The study also found that, for all suburbs, emissions were low in the morning and peaked between 4 and 10 pm on a typical winter's evening (which coincides with the onset of temperature inversion conditions in Christchurch).
Recent unpublished work by the Canterbury Regional Council suggests that about 90 percent of Christchurch's wintertime pollution from particulate matter comes from home fires, with coal fires, open wood fires and woodburners each contributing about a third of this. Motor vehicles contribute only about 4 percent. An earlier study estimated that up to 29 deaths a year and 80,000 lost work hours could be related to the fine particles in smoke (Foster, 1995). Household fires also contribute to about about 50 percent of Christchurch's wintertime carbon monoxide pollution. The Canterbury Regional Council has been developing plans to phase out open fires and bring in tougher emission standards for new woodburners.
Over the last decade there has been a switch from the majority of homes having open fires to the majority having slow combustion fires.
Source: Statistics New Zealand (1996)
Large industrial installations, such as factories and power stations, can generate considerable quantities of air contaminants from a single source. This is often more visible than the diffuse haze which arises from cars and domestic chimneys. But, although they burn more than half the solid fuels consumed in New Zealand and sometimes emit heavy metals and other chemical contaminants, their overall impact on air quality may not be so dramatic. New Zealand has relatively few large industrial emitters; these are often located at some distance from heavily populated areas and are subject to local authority rules which prohibit high emissions.
Under the Resource Management Act 1991, large emitters are controlled through air discharge permits issued by a regional council.
The permit specifies the amount that may be discharged in a given period and usually requires emissions to be monitored. Because the system is relatively new, it is not yet possible to assess the significance of industrial emissions in contributing to ambient air quality problems. In principle though, the system ought to ensure that emissions do not significantly reduce air quality.
Some of the country's biggest emitters are the Huntly power station, the Glenbrook steel mill, and the pulp and paper industry. One of these, the Tasman Pulp and Paper mill at Kawerau in the Bay of Plenty, became subject to an air discharge permit in 1994 after previously operating under a Clean Air Act licence. The mill produces 1 percent of the world's paper, 2 percent of New Zealand's export earnings, and 3 percent of our discharges of the 'greenhouse gas', carbon dioxide. Its smokestacks currently emit 450 tonnes of particulate matter per year using state of the art control technology, and approximately 1,000 tonnes of reduced sulphur compounds per year, including the 'rotten egg' gas, hydrogen sulphide, which creates a local odour nuisance. (Ninety percent of the sulphur emissions come from the plant's geothermal energy source.) Under its discharge permit, the mill is committed to reducing these emissions, and trying to eliminate the odour problem for the surrounding community.
While the vast majority of pressures on air quality tend to occur in urban areas, spraydrift from agricultural chemicals is largely a rural problem, especially where residential communities and those on lifestyle blocks rub shoulders with those involved in rural activities. Numerous complaints about spraying are received every year by government agencies, health authorities, and district, city and regional councils (Gazely and Bird, 1993; Parliamentary Commissioner for the Environment, 1993). The principle concerns are the potential for damage to susceptible non-target crops, and the perceived risk to human health either directly through spraydrift or indirectly through environmental contamination (Sheridan, 1995). Aerial spraying appears to produce a larger number of complaints than ground-based spraying, perhaps because of the greater noise and visibility of aircraft and helicopters. Another factor cited in many complaints is the chemicals' odour, which can often contribute to a complainant's perception that their health maybe at risk (Baker and Selvey, 1992).
The most widely criticised chemical sprays have been the butyl ester formulations of 2,4-D (2,4-dichlorophenoxyacetic acid) New Zealand's most widely used weedkiller (Ansley, 1996a and 1996b; Parliamentary Commissioner for the Environment, 1993; Watts, 1995). The herbicide was developed in the 1940s to control broad-leaved weeds. Its effectiveness and low cost made it New Zealand's most widely-used pasture spray.
In response to public complaints about off-target plant damage, odour, and the perceived risk to human health, regional councils in areas of high usage considered introducing restrictions on the use of this particular form of the compound and promoting other, less drift-prone, alternatives, such as 2,4-D amine formulations which have lower vapour pressures (Northland Regional Council, 1995). In October 1996 the Pesticide Board decided to ask the manufacturers and marketers of the 2,4-D isobutyl ester formulation to withdraw it and replace it with the less volatile ester formulation. Those approached agreed to the request, and the product will not be procurable after 1 October 1997. The Ministry for the Environment's Sustainable Management Fund is currently supporting research on the use and impacts of 2,4-D.
Other sources of ambient (outdoor) air emissions include:
- lead-contaminated paint dust from old buildings (see Box 6.2)
- nuisance odours from agricultural or industrial activities (see Box 6.4)
- scrub fires and agricultural burn-offs
- dust from unpaved roads, ploughed fields, quarries, road construction and building sites.