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Johannes Köbler

Marcel Mendler

NOx capture
Nitrogen oxides are a focal point of public attention. What would it be like if we could filter it directly out of the atmosphere? Audi is working with a partner company on exactly such a capturing tech­nology. A prototype will soon be entering field trials.

NOx capture can potentially make a revolutionary contribution to clean­ing the air in our cities. And it’s unobtrusive, at least visually. The new technology is packaged in a regular freight container marked only by the four rings. Toward the end of the summer, Audi aims to erect it in a busy street in Heilbronn. Alexander Krajete, owner of a startup in Linz dealing with environmental technology, explains the fundamental principle behind NOx capture: “Inside our container are three adsorber units. They’re filled with a special granulate – little dry beads of one to three millimeters in diameter. A fan sucks the ambient air into the adsorber and the NOx is captured by the beads. The air that comes back out of the container has had more than 85 percent of the NOx stripped out of it.”


Road traffic
Road traffic is responsible for a large proportion of NOx emissions. Diesel engines emit more nitrogen oxides than gasoline engines.

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85 percent or more is the degree of purification achieved by Audi’s partner, Alexander Krajete.

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Audi cooperation partner –
Alexander Krajete runs a startup in Linz (Austria) dealing with environmental technology.

The technology from upper Austria promises to be practicable and robust. Krajete again: “The process is so efficient that one fill of granulate should last for several months. Our process works just as well on very cold winter days as it does in the summer heat, and it even draws nitrogen oxides out of the air when they’re in low concentrations. The electricity costs for the fan currently amount to a few euros per day.”


A fan in the container sucks ambient air into adsorbers, which are filled with a special granulate that captures NOx. The clean air is returned to the atmosphere..

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What is NOx?

Nitrogen is crucial for life on Earth. 78.1 percent of the atmosphere is made up of nitrogen (almost all of the remainder is oxygen). Nitrogen also drives plant growth and is a fundamental element of fertilizer. However, the combustion process causes it to oxidize into vast numbers of gaseous molecules – nitrogen oxides (NOx) made up of nitrogen (N) and oxygen (O) atoms. The most important of them are nitrogen monoxide (NO) and nitrogen dioxide (NO2). Nitrogen oxides have various negative effects on people, the environment and the climate.

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Adsorber unit –
Three such cylinders filled with granulate are inside the container..

80 g

Die Anlage kann am Tag 80 Gramm NOx aus der Luft binden – so viel, wie rund 10.000 Fahrzeuge NOx ausstoßen.

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And how much NOx can the adsorber in the container store? “At its peak, we’re pulling 1,500 cubic meters of air through the system,” says Krajete. “We plan on filtering 30,000 cubic meters of air per day, capturing 80 grams of NOx. This equates to the amount emitted by 10,000 vehicles crossing the intersection every day.”

Nitrogen oxide emissions are quickly diluted in the air. At the point of emission, NOx concentration is still high, but just a light breeze is enough to disperse it and rain washes it away. Therefore, suction into the container is positioned low down and the equipment is located as close to the edge of the road as possible. The project in Heilbronn is an initial pilot test that Audi and Krajete want to use to garner information for the next development phase. But it will bring benefits to local residents and the environment from day one.

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Audi Air Capturing? Hagen Seifert, Head of Sustainable Product Concepts explains what’s involved..

Mr. Seifert, Audi has embarked on a program
called Audi Air Capturing, which relates to nitrogen oxides.
What’s the idea behind it?

Seifert: The fundamental idea is to trap pollutants from the air. And to be able to do so in high concentrations such as those from a vehicle powertrain as well as in very low concentrations such as those in ambient air.

How do you want to achieve that?

Seifert: We’re developing a whole toolkit of measures for capturing CO2, nitrogen oxides and other emissions. Different direct air capturing (DAC) processes are considered based on the concentration of these emissions, with all of them functioning on the same basic principle – the respective emissions are captured by a dry adsorber that is then simply washed with heat or water-based media. We’re already able to capture CO2 and NOx very efficiently and inexpensively – from regular ambient air, from closed spaces or from exhaust emissions.

Which route is the most promising?

Seifert: We’ve gained the most experience so far in capturing CO2 directly from ambient air. Together with Climeworks from Zürich, we’ve spent the last four years developing the necessary technology. Toward the end of 2018, this will result in a commercial facility which can capture around three metric tons of CO2 per day that will then be supplied to one of the biggest producers of soft drinks. One well-known process is also the use of CO2 in the production of synthetic fuels like the Audi e-gas facility in Werlte in Emsland. The prospects for NOx capture are also extremely promising. We’re currently working with our cooperation partner on a new kind of stationary container capable of capturing almost all the NOx emitted daily at a busy intersection in Heilbronn.

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