3 Air Pollutants Monitored

3.1 Carbon monoxide

Carbon monoxide acts on humans by inhibiting oxygen uptake in 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.

3.2 Nitrogen oxides

Nitrogen oxides incorporate several species that exist in the atmosphere, which are 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 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 NOx in most parts of the country, although power stations and other large combustion units may be significant localised sources as well.⁴

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 health effects with other pollutants such as SO₂ and particulate matter.

3.3 Sulfur dioxide

Sulfur 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 sulfur dioxide can cause stimulation of the nerves in the air passages, resulting in a reflex cough, irritation and chest tightness.

In addition, sulfur 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 more significant effect compared to people with uncompromised respiratory systems.

3.4 Volatile organic compounds

Volatile organic compounds are chemicals that easily evaporate at room temperature. The term ‘organic’ indicates that the compounds contain carbon. VOCs include a wide range of carbon-based molecules, such as some aldehydes, ketones and hydrocarbons.

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 contaminants⁵.

3.5 Particulate matter

Particulate matter (PM) can be a significant air pollutant that is associated with a variety of health and environmental effects.

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

• fine particulates (less than 2.5 μm) emitted as a result of fuel combustion such as those associated with road vehicles, power generation, industrial processes and domestic heating appliances

• particulates formed by chemical reactions in the atmosphere. These comprise largely of sulfates and nitrates

• coarse particulates (between 2.5 and 10 μm) that arise 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 particulates such as pollen.

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 solid and liquid aerosols that exist in ambient conditions.

A variety of measurements 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:

• particulate matter less than 10 μm (PM₁₀)

• total suspended particulates (TSP).

3.5.1 Particulate matter as PM₁₀

The main effect of PM₁₀ is on human health as PM₁₀ can be inhaled into the respiratory system. The coarser fractions of airborne particles are deposited in the trachea bronchial region, where asthma attacks are triggered.

3.5.2 Total suspended particulate (TSP)

TSP consists of all particles which range in size up to 50 μm in diameter. TSP is sufficiently small enough to be inhaled; however, the larger particles (10–50 μm) are readily filtered out in the nasal cavity. TSP has an effect on both the aesthetic and health quality of the ambient air.

3.6 Lead

Lead is a toxic metal present in the atmosphere in its elemental form and one of the principal 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 winter (June–August) only.

Health effects of lead in air are caused when the small particulates are inhaled or swallowed. It can harm the central nervous system, kidneys, and blood cells. Growing children and foetuses are more at risk resulting in possible physical and mental problems.