A couple of centuries ago it was normal to see dirty water streams on the streets of any city. Then it became unacceptable, as citizens became aware that they were a source of infection. Maybe one day the same will happen with the pollution of cars. Scientists are making the traces of dirt that the vehicles leave in the streets: gases and particles that cause cancers and delay in the development of children.
This is what a study published in May in the magazine has done in Barcelona Science of the Total Environment. This has shown, for example, that pollution is trapped in narrow streets that run between tall buildings, such as Travessera de Gràcia.
It has also shown that in the streets parallel to the sea, as Industry or València For example, pollution accumulates on the ground floor on the side towards the sea. Living on high floors does not mitigate these effects, depending on the job. The pollution is reduced very little between the road and the roof.
In the same way that no one would make a playground next to an open-air sewer, experts recommend Ward off from contaminated locations such as bicycle lanes or day care centers. Although they remember that the most hygienic solution is to free the cities from the pollution of the cars – as at the time they were freed from the dirty waters.
At street level and in height
"You can not dismantle buildings in the city, so it's best to reduce traffic, but as long as that does not happen, you can reduce exposure by distancing the most vulnerable," Fulvio Amato, researcher of the Institute of Environmental Diagnostics and Water Studies (IDAEA) of the CSIC and co-author of the work.
The researchers placed meters on the street and on the roofs of two dozen buildings. Thus, they measured how pollution is reduced as one moves away from the road, both in horizontal like in vertical.
Specifically, they measured concentrations of black carbon and NO2, substances emitted mainly by diesel, which is used in half of the private cars of Barcelona.
Never like in a park
The measures reveal that, in general, you have to get away 25 meters from the edge of the street so that pollution is reduced by half, and 67 meters so that it reaches the level of an urban park.
This last distance is almost never reached in Barcelona, because before there is usually another street with traffic. "Also, those distances vary a lot depending on the geometry of the street, the wind and the traffic ", says Amato.
For example, at a time when there is the same traffic on the Diagonal and Travessera de Gràcia, there will be more pollution on the second street, which looks like canon of a river. In the first, the wind will spread pollutants more.
The study also finds that contaminants accumulate in the side towards the sea of the streets parallel to it. This is due to the dynamics of the vortices inside the buildings canyon.
Finally, you have to climb to heights higher than 26 meters to reduce pollution by half. But Barcelona's buildings are only 21 meters high on average.
"The quantitative understanding of these variations, offered by the article, is something sensational to minimize exposure," he says. Lidia Morawska, director of the International Laboratory of Air Quality and Health of the World Health Organization (WHO), not involved in the work.
Amato suggests moving the bike lanes and playgrounds away from the road. "It does not have to be much: the main problem is in the first meters"Another suggestion is to place the classrooms as high and away from the possible street." Amato also remembers that there is a lot of variability of geometries and that before worrying, local measures must be taken.
"The buildings are there and you can not change the physics of the wind, you have to reduce emissions," he concludes. Jennifer Richmond-Bryant, researcher at the University of North Carolina, not involved in the work.
(tagsToTranslate) pollution Barcelona study spatial distribution