The Faustian Bargain - Health or Economic Growth
Every day politicians and scientists make trade-offs between our health and GDP. Today NOx (nitrogen oxides) and PM (particulate matter), which are emitted from engines are seen as a necessary evil, as they literally fuel economic growth. They are also known however to cause smog and acid rain. Both are easily inhaled and both damage lung tissue. A UK study found that mortality increases 7% with each 5 micro-gram increase in PM.
The effects are so severe that cities in China are closed on a regular basis because the air is too unhealthy to breathe, affecting hundreds of millions of people. Hospitals are reporting surges in children with respiratory diseases. The world health organization defines a safe level of PM at 25 micrograms per cubic meter, but China regularly reaches levels as high as 500. Beijing airport sometimes has a visibility of only 300 metres due to smog, and the city often closes down roads.
Because of these threats regulators worldwide are getting tough on NOx and PM with regulations tightening in waves to allow industry time to adjust. Cleaning up our engines is expensive and it is not optional. We have both a legal and moral obligation to comply.
The Quick Fixes
There is no doubt that this is a true crisis, and yet a real solution remains elusive. Today manufacturers deal with emissions at the exhaust or reduce their production during combustion:
SCR (selective catalytic reduction) is an after-treatment where NOx is neutralized at the exhaust by combining it with urea. The problem with this technology is that it is expensive and requires the user to carry a urea supply. PM is dealt with using a DPF (diesel particulate filter), but it requires a low level of sulphur in the fuel which is not always possible. SCR is also known to malfunction in cold temperatures.
EGR (exhaust gas recirculation) reduces NOx creation in the engine by cooling some exhaust gas and recirculating it back into the air intake of the engine, resulting in lower oxygen and nitrogen and a lower temperature inside the combustion chamber. NOx is formed at high temperature and hence the lower oxygen/nitrogen combined with lower engine temperature reduces NOx formation. The problem with EGR is it reduces engine performance and also increases PM because it decreases the efficiency of combustion.