3 Air Pollutants Monitored
3.1 Particulate matter
Particulate matter is an air pollutant that is associated with a variety of health and environmental effects.
Sources of particulates vary widely from location to location and reflect the wide range of emission sources of particulate concentrations in New Zealand. Typical sources include:
- fine particulates that result from fuel combustion such as those associated with road vehicles, power generation, industrial processes, domestic heating appliances, etc
- particulates formed by chemical reactions in the atmosphere. These comprise largely of sulphates and nitrates
- coarse particulates from a wide range of sources, including re-suspended dusts from road vehicles, construction works, mineral extraction processes, wind-blown dusts and soils, sea salt, and biological particles such as pollen.
There are a variety of measures which 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 diameter of 10 µm or less can be inhaled into the respiratory system. The main effect is on human health. The coarser fraction of airborne particles (2.5 µm to 10 µm) is 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 category, encompassing a wide range of chemically and physically diverse substances. Particulate matter includes all solid and aerosol matter that exists in ambient conditions.
3.1.2 Total suspended particulate (TSP)
TSP consists of all particles which range in size from 50 µm diameter downwards. Particles larger than 50 µm are too large to remain airborne for extended periods and thus form deposited particulate.
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 has an effect on both aesthetic and health quality of the ambient air.
3.2 Lead
Lead is present in the atmosphere in its elemental form and one of the principle sources has been motor vehicle emissions. Historically, lead was included in petrol as a catalyst for combustion but has been removed from fuel supplies since 1996.
As a result atmospheric concentrations of lead have dropped markedly since this time and, to reflect this, in October 2000 monitoring of lead was reduced from monthly samples to samples taken over a three-month period during the winter (June-August) only.
3.3 Sulphur dioxide
Sulphur dioxide is an acidic gas with a pungent odour. It 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 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 of objectionable levels of vehicle exhaust fumes.
3.5 Nitrogen oxides
Nitrogen oxides incorporates several species that exist in the atmosphere, collectively referred to as NOx. 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 the NOx 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.
NOx 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).
