At the present time hardly a day goes by without something to read on the subject of nitrogen oxide (NOx). In the exhaust emissions scandal which first hit the headlines in connection with the Volkswagen Group and in the meantime has now come to affect the whole of the automotive industry, people are talking about nitrogen monoxide (NO) and nitrogen dioxide (NO2). It has now been established that many diesel engines fitted in motor cars and trucks release considerably more of these poisonous gases than originally declared, and partly by several hundred per cent. According to a survey carried out by the German Federal Environmental Agency, Euro 5 Diesel vehicles are emitting on average 906 mg NOx into the air instead of the permitted 180 mg per kilometer. And even modern Euro 6 Diesels release an average of 507 mg/km instead of the allowed 80 mg/km.
The current annual limit value for nitrogen oxide in Germany is 40 micrograms per cubic meter air (µg/m³). There is a good reason for this. It is particularly nitrogen dioxide which irritates the respiratory tract, affects the function of the lungs and with a longer lasting higher concentration can lead to serious cardiovascular diseases which can lead to death. According to information from the German Federal Environmental Agency, the limit value was exceeded at roughly 60% of the urban measuring stations. Something which is less well-known is that in the cars themselves the concentration is often considerably higher than at an urban station nearby measuring the ambient air. A survey conducted by Heidelberg University found out that the vehicle occupants often sit in nitrogen oxide concentrations ranging from 90 µg/m³ in the city, 150 µg/m³ on the autobahn and up to 300 µg/m³ in tunnels. The main reason for this is that the car ventilation system sucks in the exhaust emissions of the cars in front which in tunnels are especially highly concentrated. If one considers that already a continuous concentration of 100 µg/m³ frequently leads to respiratory disorders, the general picture doesn’t look good.
However, already today we can do something about it. The key word here is the cabin air filter. In short, if the cabin air filter is coated with activated carbon, it can reduce the concentration of the harmful NO2 in the cabin by more than 80%. If the air conditioning system of the car is run in recirculation mode, the reduction effect is even stronger. How does that work?
Depending on the type of vehicle, a cabin air filter from MANN+HUMMEL on average contains 100 to 200 grams of highly activated carbon. The carbon forms a closely meshed pore system which has an internal surface area of approximately 1,000 square meters per gram of activated carbon. 100 gram of activated carbon in the filter therefore results in a total area which is comparable to the area of ten football pitches. When nitrogen oxide reaches the activated carbon a part remains in the pore system and is physically adsorbed, i.e. it remains stuck on the surface. A further part reacts with the water adsorbed on the surface from the ambient humidity and is chemically bound. In addition, the considerably more poisonous NO2 is reduced in a catalytic reaction to NO which has a further positive effect. All in all this results in a reduction in NO2 of more than 80% in comparison to conventional particulate filters without a coating of activated carbon, for an additional cost of roughly five euros.
As mentioned before, a cabin filter in fact does not solve the actual problem. This is a challenge for vehicle producers and politicians, who are already working on possible solution scenarios. But cabin filters today are already able to protect vehicle occupants from poisonous gases. As well as the very topical nitrogen oxide, activated carbon also binds hydrocarbons, sulfur dioxide and ozone which are also not good for human health. Furthermore, they filter particulate matter and with our latest filter generation FreciousPlus even retain almost all allergens. At the same time the special coating prevents the growth of bacteria and mold fungus.
So you see, even though cabin filters do not contribute much to the image of a car, their function is nevertheless important. They are usually replaced with every service and we recommend replacement every 15,000 kilometers or once per year. It’s worth it – also and especially for your health.