Sign of a superpolluter. Click to enlarge. Credit: Credits: Philip Siegmann-UAH/SINC

The report concludes that were these vehicles removed from the flow of traffic, the total active surface (TAS) concentration of the nanoparticles (the particle surface that interacts with the environment) could be reduced by up to 25%, and the concentration of particulate polycyclic aromatic hydrocarbons (PPAH) absorbed by the nanoparticles, which are known toxic substances, could be reduced by up to 48%.

Usually you can see the ‘super-polluters’ simply just by looking; particularly when they accelerate or climb a hill and a cloud of smoke comes out of the exhaust pipe. People usually complain about the bad smell and the smoke, but the worst thing is that the nanoparticles that nobody can actually see or smell are always present in Madrid, for example, even when you think that you are breathing in clean air.

—Philip Siegmann, Department of Signal Theory and Communications at the University of Alcalá (UAH) and co-author

The study, published recently in the journal Atmospheric Environment, has focused on distinguishing and quantifying which types of vehicles have a higher emission rate of ultrafine nanoparticles (<100 nm) that are implicated in the development of different diseases. Their reduced size enables them to be distributed within the body with hardly any detection by the defences of the organism, and can even cross the cell membranes. Some studies have already shown that these small particles stimulate allergic reactions, such as asthma, and the development of multiple sclerosis. Moreover, under continued and prolonged exposure, they can produce cancer.

The researchers noted that one of the main emission sources of these ultra-fine particles comes from diesel powered vehicles, but this is less so for gasoline-powered vehicles.

To obtain measurements, the scientists followed moving vehicles and, through the window, recorded the data using two sensors located at the end of a tube. The recordings were taken every ten seconds and were made by sucking in the air so that the sensors could pick up the measurement peaks when they entered the trail of smoke emitted by a vehicle. In the case of the super-polluters, the PPAH measurement peaks ranged from 100 to 1,000 nm/m³, but in some cases this even exceeded this high quantity.

The study data were taken in Madrid in 2001 and 2006 and in Mexico City in 2001, one of the most polluted cities in the world. Although they do not appear in the report, measurements were also taken in Boston (USA). The highest number of emissions of nanoparticles corresponded to Madrid, and the scientists relate the data to the fact that a high percentage of the cars in this city are diesel (nearly 30% in 1999-2001 and 50% in 2006), whereas in Boston there are fewer emissions of this type because nearly all the vehicles travelling on the roads are gasoline driven. Mexico City finds itself in the middle, although there is a plethora of super-polluters in this city.

Nevertheless, in Madrid, the results confirm that over the last 6 years pollution from nanoparticles has reduced by nearly 65%. The researchers say this is because of the improvements that have been incorporated into new vehicles in order to comply with the European regulations regarding emissions, such as the Euro 4 level which will be replaced by the Euro 5 level in 2009.

Resources

• P. Siegmann, F. J. Acevedo, K. Siegmann, S. Maldonado-Bascón. “A probabilistic source attribution model for nanoparticles in air suspension applied on the main roads of Madrid and Mexico City”. Atmospheric Environment 42 (17): 3937–3948, 2008 doi: 10.1016/j.atmosenv.2007.05.021