New Zealand Engineering 1997 May

Auckland Air Quality - Can we breathe easy ?

Michelle Wilkinson is an air quality technician working at NIWA, Auckland.

Dr Gerda Kuschel is an environmental engineer working in air quality at NIWA, Auckland.

Michael Bird is an air quality scientist working for the Auckland Regional Council.

In Auckland where more cars are owned per capita (see Figure 1) and motorists travel double the kilometres of motorists elsewhere in New Zealand, people are becoming increasingly concerned about their exposure to air pollution. Can we really breathe easy in Auckland?

In New Zealand, we currently experience reasonably good air quality in our urban, rural and coastal areas, primarily due to a number of factors that work in our favour. We have a relatively low level of industrialisation and New Zealand's geography and meteorological conditions favour the dispersion of pollutants.

However, in some locations, such as Auckland and Christchurch, the air quality is at times already degraded, whilst in other centres it is under threat. With the trends in population growth observed (7.2 percent increase for New Zealand and 13.2 percent increase for Auckland between 1991 and 1996¹) and increasing industrialisation, air quality will become vulnerable in the future.

What is air quality

Air quality is the measure of the cleanness of our surrounding air. As we all need to breathe air to survive, the cleaner the air the better it is for us. Air quality can be affected by emissions from a number of sources. These include industrial areas, motor transportation, domestic households, and natural sources such as tidal mud flats and geothermal activity.

Maintaining a high standard of air quality contributes a great deal to our quality of life. Clean air benefits both people and the surrounding environment by providing aesthetic value through improved quality of life, and direct economic value through activities such as tourism.

Tourism is one of our major export earners, and in order to maintain our current image it is vital that we continue to have good visibility. This is important to the perception of this country as a clean environment. The economic benefit of tourism is spread throughout the country.

Sulphur oxides, nitrogen oxides and particulates can pollute streams and lakes when they are emitted into the air. This can place recreation areas at risk for swimming and fishing and can also result in a loss of aesthetic value.

In many countries where air quality is poor, the population's health is affected. This results in lower productivity as work days are lost and health care costs accumulated. Commercial harvests can also be affected by a reduction in air quality, resulting in crop, timber and stock losses.

New Zealand has many indigenous species about which not much is known with regard to their vulnerability to varying types and concentrations of pollutants in the air. If air quality degrades we may see sensitive populations disappearing.

Particulates soil buildings, sulphuric and nitric acids corrode construction materials and burn coatings and paints, resulting in additional costs being incurred for building maintenance.

Air quality guidelines

Air quality guidelines are developed to provide "a basis for protecting public health from adverse effects of air pollution and for eliminating, or reducing to a minimum, those contaminants of the air that are known or likely to be hazardous to human health and well-being"².

Ambient air quality guidelines refer to the air outside buildings or structures and does not include indoor air or air in the workplace. New Zealand's guidelines³ were developed by the Ministry for the Environment, and are guidelines only, not standards. It is up to local authorities to either accept these guidelines as local standards or modify them to suit their geographical and meteorological conditions. These guideline levels are not maximum discharge levels for industry to pollute up to. They are there to provide a basis for protecting public health and the environment from the adverse effects of air pollution.

Ambient air quality pollutants are those substances that can have a direct and adverse effect on the local environment (including plants, animals, and occasionally man-made structures) but generally exhibit no carcinogenic health effects. New Zealand has one of the highest asthma rates in the developed world. In a recent address, the Minister of Health was quoted as saying that 20 percent of the population suffer from asthma to some degree. Consequently those ambient pollutants which adversely affect the human respiratory system are of particular concern in New Zealand.

Some of the substances classified as ambient air quality pollutants in Auckland, their associated health effects and main sources are listed below:

• Fine particulate matter less than 10 mg in diameter (PM 10 ) When exposed to particulates in the air lung function can be reduced, and in extreme cases, the development of cancer has been attributed to high levels of particulates. The main sources of particulates are motor vehicles, domestic (such as home heating) and industry (see Figure 2a).

• Carbon monoxide (CO) It is readily absorbed from the lungs into the blood stream resulting in the decreased oxygen carrying efficiency of blood; in severe cases this can lead to asphyxiation. Neurological symptoms can also be detected, and these include dizziness and headaches. The main sources of carbon monoxide in the air are motor vehicles and industry (see Figure 2b).

• Sulphur Dioxide (SO 2 ) This gas is a known asthma trigger, causing sudden constriction of the airways. It also affects respiratory function in non-asthmatics. The key sources of this gas are motor vehicles, industry and domestic (home heating) (see Figure 2c).

• Nitrogen dioxide (NO 2 ) When this gas enters the respiratory system it increases the susceptibility to, and the severity of, infections and asthma. Long-term exposures can lead to a weakening of the lungs' defences against bacterial infection. Home heating (domestic) and motor vehicles are the main sources of this pollutant (see Figure 2d).

• Ozone (O 3 ) Ozone has been identified as a lung irritant, and exposure to it can lead to reduced lung function. It is formed from nitrogen oxides and organic compounds reacting in the presence of sunlight (UV). It is usually associated with heavily populated industrialised cities with high numbers of motor vehicles and industry.

Air quality monitoring

Monitoring the air for pollutants is difficult because the atmosphere is three-dimensional and largely unconstrained. Many pollutants are present in very low concentrations and some undergo complex chemical processes over short time scales. Also, air quality is greatly affected by the weather, which is difficult to predict. As a result, the determination of a monitoring programme, the choice of methods, the sites, and the use of the results are all specialised tasks.

Monitoring is undertaken for a number of reasons. Some pollutants are obvious, strong odours and particulates can easily be sensed by much of the population. However, there are many contaminants which are not easily detected and have cumulative effects which may not be obvious until many years after exposure. Others may not have direct effects, but may alter the long-term balance.

Monitoring is also very valuable for detecting trends. For example, levels of a contaminant may be low initially, but a significant upward trend may indicate problems for the future. Also identifying daily and seasonal fluctuations is useful for distinguishing between pollution events and recognised trends.

Monitoring is used to determine where the ambient levels of a pollutant are in comparison to the national guidelines. Regional councils are required under the Resource Management Act to maintain sustainable air quality in their regions, and most of them have adopted the ambient air quality guidelines as regional guidelines.

Compliance monitoring is used by councils to ensure that existing industry is meeting emission requirements.

Special interest cases also use monitoring to determine existing levels in order to discover if additional industries are viable. Basically, monitoring is required to know, rather than guess, what is in the air.

Monitoring techniques can range from simple gas specific filters (passive samplers) that cost around $200 per pollutant and give a monthly average, to sophisticated open path monitoring systems (differential optical absorption spectrometry) which cost about $200,000 and give real time measurements of multiple pollutants simultaneously, and can be designed to be moved from site to site. However, the most commonly used techniques are continuous monitors that are specific to one pollutant, provide real time data, remain fixed at one site, and cost between $20,000 and $40,000.

Air quality in Auckland

One of the main types of pollution of concern in Auckland is brown haze. One component of brown haze is photochemical smog. Photochemical smog, is the result of nitrogen oxides combining with oxygen and volatile hydrocarbons in the presence of sunlight. The characteristic brown colour is caused by nitrogen oxide gases. One major contributor to photochemical smog is motor transport emissions.

Photochemical smog is the source of many oxidant pollutants, including ozone, nitrogen dioxide and aldehydes, which can build up to high local levels in still air conditions. There are a number of ways to monitor the build up of photochemical smog and they include analysing the air for ozone and nitrogen dioxide. Days in which high levels of these pollutants are detected are often indicative of a photochemical event taking place.

Photochemical smog can develop in Auckland when sea breezes blowing inshore from the west and east concentrate rather than disperse air pollution, which then undergoes the chemical reactions facilitated by sunlight.

Los Angeles style photochemical smog was first detected in Auckland in the late 1970s. The number of days in which photochemical events take place varies depending upon the weather conditions. On average Auckland experiences photochemical build up only a few times a year. This compares with Sydney with an average of 20 photochemical smog days a year, Adelaide and Perth with two to ten photochemical smog days a year, and Los Angeles in which a third of the days of the year experience photochemical build up.

With the elevated concentrations that are typically observed in the less windy La Nina years, and given that Auckland and its motor vehicle fleet is growing quite rapidly, there is the potential in the future for higher and more frequent concentrations of photochemical pollutants to develop.

Many of the pollutants identified as being important in the New Zealand environment originate from transport emissions. Private motor vehicles have been identified as the dominant contributor to transport emissions, and to the air shed. Transport emissions are estimated to vary significantly with the season and day of the week. With Aucklanders having about 500 cars per 1000 people, compared to Los Angeles County with about 540 cars for every 1000 people and metropolitan Sydney with about 450 (see Figure 1), the potential for an increase in pollution events is growing. The annual increase in the number of vehicles on New Zealand roads is estimated by the Land Transport Safety Authority as being three percent.

There is greater pressure on air sheds due to increased population and transport issues. To address this and the RMA requirements, the Auckland regional council and other regional councils in New Zealand are developing air emissions inventories⁴ to assist with determining appropriate, effective and equitable reduction strategies.

With monitoring data and an understanding of the nature of the source, emissions inventories can be used to identify the main contributors, determine the effectiveness of any action proposed, and provide a baseline assessment of future trends.

Compared to large overseas cities, the maximum levels of pollutants that Auckland records seem low. However, many are showing an increasing trend with higher and higher values being measured.

The maximum one hour concentrations recorded in Auckland in 1996 for ozone and nitrogen dioxide (indicators of photochemical smog) are below the national ambient air quality guidelines. They also compare favourably with the maximum levels recorded overseas (see Figure 3).

Exceedences of the eight hour New Zealand guidelines occur for carbon monoxide, with the maximum value recorded being 13 mg/m³. This level is not too far below that recorded for Southern California (see Figure 4).

The maximum level of PM 10 particulates in Auckland is well below the New Zealand guideline, and below the value recorded in Southern California (see Figure 3).

Equipped with a variety of air quality management tools, such as monitoring information and emissions inventories, more is being learnt and action taken to address air quality in Auckland and New Zealand, so that we can all breathe easy in the future.

References

1. Statistics New Zealand. Census 1996. Statistics New Zealand, 1997.

2. World Health Organisation (WHO). Air Quality Guidelines For Europe. WHO Regional Publications, European Series, Number 23. Copenhagen, 1987.

3. Ministry for the Environment (MfE). Ambient Air Quality Guidelines. Ministry for the Environment, Wellington, 1994.

4. Auckland Regional Council.......Auckland Air Emissions Inventory, in prep