Published: 06 December 2016 Tuesday, 07:04 AM
Bonn, Dec 05 (deutschenews24.de/dpa) -- The city had tried just about everything to curb high air pollution, much of it from motor vehicle exhaust. It imposed speed limits, required cars to have an emissions sticker certifying they meet environmental standards, and promoted travel by bus and train.
Stuttgart, a car industry hub in Germany and home to Porsche and Mercedes-maker Daimler, nevertheless still has that traffic odour.
It lies in a bowl that often traps particulate matter (PM), which includes dust, dirt, soot, smoke and liquid droplets.
Now the city, in what seems like an act of desperation, is calling nature to the rescue: A 100-metre-long wall of moss is going up in a scientific experiment in extracting the harmful particles from the air. If it works, moss may soon be coming to a wall near you too.
Stuttgart authorities say the enormous surface area of the spongy plant`s millions of tiny leaves can collect PM electrostatically.
And, they add, the moss can absorb ammonium nitrates - which make up as much as 50 per cent of PM - and convert them into plant mass.
"We aim to test whether it`s really able to improve air quality in a street," said Jan Knippers, a professor at the University of Stuttgart`s Institute of Building Structures and Structural Design.
Two test sections of wall a few metres long have been set up so far at a major road junction near the city centre. By March the complete wall - an aluminium frame onto which moss mats are screwed - is to be in place. Several metres away is a pollution-measuring station.
European PM limits have been exceeded in Stuttgart this year, as in other years, along with those for the pollutant nitrogen dioxide.
Next year, four measuring sites near the moss wall will show what the little plant can do.
"If particulate matter can be reduced in a wide area, it`ll make sense to deploy moss walls in the city to combat it," remarked Fritz Kuhn, the mayor of Stuttgart, Germany`s sixth-largest city with 610,000 inhabitants.
"Utter nonsense" says Environmental Action Germany (DUH), an environmental and consumer protection NGO that has been fighting in court for years to ban cars so as to clean up the air in German cities.
It said the moss wall would look good but ultimately be ineffective, and that the city knew this. To improve air quality long term, vehicular traffic must be excluded from cities, it argues.
If cities don`t do this, they`ll be legally forced to, declared the DUH`s chief, Juergen Resch. He said Stuttgart was obligated to ensure that EU pollution limits were met everywhere in town, and that "moss walls will surely play no role."
"It`s a pilot project whose outcome is unclear," noted Stuttgart climatologist Ulrich Reuter. He said similar experiments had been conducted elsewhere, but the Stuttgart project, will be the first in Germany to be scientifically monitored.
It`s not only aimed at determining once and for all whether moss is effective in absorbing PM from motor vehicles, but also which moss types are best suited for this.