Car tax changes could hurt air quality in parts of Helsinki

Nitrogen oxides from diesel cars could increase

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By Anna-Leena Pyykkönen
     
      The upcoming changes to car taxation, which have been promoted as environmentally friendly, may not necessarily lead to cleaner city air.
      The tax reform favours diesel-powered cars, which have lower carbon dioxide emissions, but could lead to an increase in dangerous nitrogen dioxide in streets in the centre of Helsinki.
      Already now the maximum levels set for nitrogen dioxide can sometimes be exceeded in the centre of Helsinki and along large highways.
     
Small airborne particles which have also long plagued Helsinki residents would also continue to be a problem.
      The tax reform would favour cars with diesel engines, in which particle emissions are much higher than with a petrol-fuelled car, if no particle filter is installed.
      Not all new diesel cars have particle filters, and no tax measures have been moved forward to encourage their use.
      Under European Union exhaust gas rules, particle filters are required in all new models by the autumn of 2009, and in all cars sold as new in 2011.
     
Suspicions raised by climate and emissions experts stem from the higher nitrogen oxide emissions that are permitted for diesel engines than for petrol engines. Even after tighter rules are put in place, the difference will remain considerable.
      Some even fear that air quality could grow worse in Helsinki. Others are more cautious, preferring to wait until the real emission levels can be measured. The Technical Research Centre of Finland (VTT) is currently measuring nitrogen dioxide emissions.
      "A good thing about the reform is that it will probably push older cars out of traffic. If diesel cars become more popular, the clear problem is that their filters will not clean away nitrogen dioxide", says Jari Viinanen of the Helsinki City Environment Centre.
      Viinanen fears that "when one emission is reduced, the other is increased".
      Not even those preparing EU legislation noticed this. The emission limits have been given for the total combined amount of nitrogen monoxide and nitrogen dioxide, which does not take into account the effect they have on urban air in particular.
     
Special researcher Juhani Laurikko of VTT feels that much remains uncertain.
      The final result from the point of view of air quality depends on how cars are sold and what the emissions in new diesel cars are really like.
      He points out that filtering technology has been in use in new cars for more than ten years, but that the nitrogen dioxide levels in urban air have not gone down. "Technology does not affect nitrogen dioxide emissions as well as had been assumed", Laurikko notes.
     
Nitrogen dioxide coming straight from a car exhaust pipe is the most harmful from the point of view of health and the environment.
      Exhaust gas which passes through the catalytic converters of cars with petrol engines mainly contains nitrogen monoxide. It turns into the more harmful nitrogen dioxide only when it bonds with oxygen.
      This usually takes a few hours, unless the ozone level in the air is high, which speeds up the reaction.
      During that time, the emissions get a chance to be diluted in the air and to drift away from busy thoroughfares, which means that overall level of the harmful gas in the air is reduced.
     
Helsingin Sanomat / First published in print 10.11.2007


Previously in HS International Edition:
  Emission-based car tax to bring down price of new vehicles next year (2.11.2007)
  Helsinki considers restrictions on car traffic because of increased air pollutants (27.1.2006)
  Sudden and deep decline in air quality in Helsinki region (23.11.2005)
  Poor air quality caused by cold weather, street dust, and exhaust fumes troubles Helsinki residents (17.3.2005)

ANNA-LEENA PYYKKÖNEN / Helsingin Sanomat
anna-leena.pyykkonen@hs.fi