3 Air Pollutants Monitored

3.1 Particulate matter

Sources of particulates vary widely from location to location reflecting the diverse range of emission sources that contribute to particulate concentrations in New Zealand. Typical sources can include:

• fine particulates emitted as a result of fuel combustion such as road vehicles, power generation, industrial processes, domestic heating appliances etc
• particulates formed by chemical reactions in the atmosphere, comprising mainly sulphates and nitrates
• coarse particulates arising from a wide range of sources, including re-suspended dusts from road vehicles, construction works and mineral extraction processes, wind-blown dusts and soils, sea salt and biological particles such as pollen.

There are a variety of measurements that can be used to determine the different health and environmental effects of particulate matter. As part of the GEMS/AMIS programme two particle size fractions are monitored:

• fine particulates (PM₁₀)
• total suspended particulates (TSP).

3.1.1 Fine particulates (PM₁₀)

As described above, particles with a diametre of 10 μm or less can be inhaled into the respiratory system and affect human health. The coarser fraction of airborne particles (2.5 to 10 μm) are deposited in the trachea bronchial region where asthma attacks are triggered.

Particulate matter refers to numerous substances that exist in the atmosphere. It is a somewhat complex pollutant, encompassing a wide range of chemically and physically diverse substances. Particulate matter includes all solids and aerosols that exist in ambient conditions.

3.1.2 Total suspended particulates (TSP)

TSP consists of all particles that range in size up to 50 μm in diametre. TSP is sufficiently small to be inhaled, however the larger particles (10-50 μm) are readily filtered out in the nasal cavity. Particles 10 μm and less can be drawn into the respiratory system. TSP affects both the aesthetic and health quality of the ambient air.

3.2 Lead

Lead is a toxic metal emitted into the air both from motor vehicles that use leaded fuel and some industries. Since lead was removed from fuel in 1996, concentrations of lead in the air have dropped markedly. In October 2000, monitoring of lead was reduced from monthly samples to samples taken over a three-month period during winter only (June - August).

3.3 Sulphur dioxide

Sulphur dioxide is an acidic gas with a pungent odour which is mainly produced by the burning of fossil fuels. The gas is quite corrosive and can cause damage to buildings and other materials.

It can also have significant effects on the human respiratory system. Inhalation of high ambient concentrations of sulphur dioxide can cause stimulation of the nerves in the air passages, resulting in a reflex cough, irritation and chest tightness.

In addition, sulphur dioxide can also cause narrowing of the air passages, particularly in people suffering from asthma and chronic lung disease. These people frequently have narrowed airways, and any further restriction will have a disproportionately large effect compared to people with uncompromised respiratory systems.

3.4 Carbon monoxide

This colourless, odourless, toxic gas is formed as a product of incomplete combustion in the burning of fossil fuels. The main sources in most parts of New Zealand are motor vehicle exhaust emissions, and, as such, elevated levels are mainly found in areas of significant traffic congestion, particularly at busy intersections on inner-city streets.

Carbon monoxide acts on humans by displacing oxygen from the blood. Prolonged exposure at moderate levels can lead to symptoms such as headaches and dizziness, while at high levels it can lead to loss of consciousness and even death. At the lower levels typically encountered in urban areas, carbon monoxide measurements can serve as a useful indicator for objectionable levels of vehicle exhaust fumes.

3.5 Nitrogen oxides

Nitrogen oxides incorporates several species that exist in the atmosphere which are collectively referred to as NO_x. The two main oxides are nitrogen dioxide (NO₂), which is of concern due to its potential to cause health effects, and the monoxide form nitric oxide (NO), which is less toxic but may oxidise to NO₂ in the atmosphere.

Nitrogen oxides are formed in most combustion processes by oxidation of the nitrogen present in the atmosphere. Nitric oxide is the predominant primary product but, as indicated, this can then be oxidised to nitrogen dioxide in ambient air. Emissions from motor vehicles are the major source of NO_x in most parts of the country, although power stations and other large combustion units may be significant localised sources as well.

The main health effects of the oxides of nitrogen are due to NO₂ which is a respiratory irritant. Nitric oxide is believed to be quite harmless at the levels normally encountered in urban air.

NO_x is also an important air pollutant because of its role in photochemical smog. NO₂ is a reddish brown gas and has synergistic effects with other pollutants such as SO₂ and particulate.

3.6 Volatile organic compounds

Volatile organic compounds are chemicals that easily evaporate at room temperature. The term 'organic' indicates that the compounds contain carbon.

To rationalise air quality guidelines, the Ministry for the Environment has compiled a list of priority contaminants based on a review of international literature. The priority list includes the volatile organic compounds (VOC) benzene and 1,3-butadiene and provides ambient air quality guidelines for these contaminants (MfE 2002).