Chris de Freitas: Unseen enemies in exhaust

The Herald has fallen into the same trap as many of the public and those in government: confusing greenhouse gas emissions with air quality.

An editorial this week noted that "Decisive action ... is required if the Government wishes to significantly improve air quality by reducing greenhouse gas emissions from vehicles." Testing exhaust emissions is an air-pollution issue. None of the main greenhouse gases are pollutants. The greenhouse gas emitted from motor vehicles is carbon dioxide.

All green plants live and grow by absorbing carbon dioxide from the atmosphere. Low levels of the gas in the Earth's atmosphere limit photosynthesis and thus plant growth.

It is not uncommon for greenhouse farmers to improve conditions for crop growth by injecting carbon dioxide into their greenhouses to levels almost three times the concentration outside.

There is good evidence to prove that increases in carbon dioxide concentration in the atmosphere over the past 70 years has enhanced plant and tree growth. It is frequently referred to as the great "greening of the Earth", a response to the many biological benefits provided by the ongoing rise in the atmosphere's carbon dioxide content.

When it comes to motor-vehicle exhaust emissions, many people are surprised to learn that a poorly tuned engine emits less carbon dioxide than when it is well-tuned. An engine that is running at a nearly ideal air/fuel ratio of 14.5:1 will show about 14.5 per cent carbon dioxide and 2.5 per cent oxygen in the exhaust.

As combustion efficiency decreases, the oxygen content in the exhaust rises and carbon dioxide falls. This translates to an over-rich or over-lean air/fuel ratio, poor compression, or an ignition problem.

Nevertheless it is true that driving a motor vehicle is the single most polluting thing that most of us do. It is also true that New Zealand is the only country in the OECD without effective vehicle-emission control standards and vehicle checks.

Hundreds of people in New Zealand die each year from air pollution and many more get sick from it. A study carried out for the Ministry of Transport five years ago estimated that 970 people over 30 die prematurely each year from exposure to air pollution and 436 of these deaths occur in the Auckland region. The source of most air pollution in the Auckland urban area is vehicle emissions.

So what is the Government's plan of action? The answer reflects the Government's naivete in dealing with this serious matter. From October 27, subjective assessment of exhaust emissions will be based on visual evidence of smoke during routine warrant-of-fitness tests.

This is consistent with the so called "10-second rule" that took effect in March 2001. The legislation allows police to issue a $150 fine to the driver of any motor vehicle that emits smoke for 10 seconds or more.

This will do little to improve air quality, because most motor-vehicle emissions are too small to see. In fact, the most dangerous ones are invisible. They include oxides of nitrogen, carbon monoxide and hydrocarbons as well as invisible particulate matter. Even well-tuned diesel engines cause invisible pollution in the form of particles smaller than 10-millionths of a metre. Called PM10, they are especially dangerous as they penetrate deep into the sensitive lining of the lungs.

Asthmatics and people with heart and lung disease are particularly susceptible. A high concentration of PM10 is associated with an increase in hospital admissions and lost work days.

Alert levels for PM10 are reached at all air-pollution monitoring sites in the Auckland region. PM2.5 is four times smaller than PM10 and is even more damaging to human health. There are regular breaches of guidelines for PM2.5. PM10 and PM2.5 have no "safe threshold".

Invisible nitrogen dioxide affects the respiratory system, irritates the lungs, worsens asthma and lowers resistance to infections. It is also suspected of forming carcinogens and mutagens in combination with other substances.

Another poison emitted by motor vehicles unchecked in New Zealand is carbon monoxide (CO). CO interferes with the blood's ability to absorb and circulate oxygen and can be lethal.

At certain concentrations CO can affect people with heart conditions such as angina and can impair co-ordination and concentration. Auckland's figures for CO have been compared with London's for the period 1998 to 2004. The results show that CO concentrations in London are declining steadily; this is not the case in Auckland.

It's ironic, given that, for so many years, the Government has been falling over itself to win over support for the Kyoto Protocol, a costly and highly debatable policy which most countries have decided not to implement.

* Chris de Freitas is an Associate Professor in the School of Geography, Geology and Environmental Science at the University of Auckland.