Charcoal air filters improve in-vehicle air quality

The report by WM Air, the West Midlands Air Quality Improvement Programme at Birmingham University, shows that charcoal filters, which cost around £10-£20, can effectively remove nitrogen dioxide (NO2) from the air within vehicle cabins.

NO2 is a common air pollutant that can aggravate diseases such as asthma and increase the risks of respiratory infections. Traffic emissions are a dominant source of NO2, and so road users inside vehicles are exposed as air circulates into vehicle cabins from outside through open windows and ventilation systems.

While ventilation systems do currently filter air, this is typically via a pollen filter. These prevent tiny particles and pollen getting inside the vehicle, but they have little effect on gases such as NO2, the Birmingham team explained.

The activated carbon filters, in contrast, remove NO2 through adsorption, in which the NO2 reacts with the carbon to stick to the surface area of the filter.

According to the team, as with the pollen filter, the effectiveness of the carbon filter decreases over time, meaning it should be replaced regularly when the vehicle is serviced.

“Our findings show clearly that there are benefits to switching to activated carbon air filters, reducing exposure to NO2 and the risk of related adverse health effects,” said lead researcher Dr Vasileios Matthaios.

“These filters are simple, effective and inexpensive and should be considered, particularly for people who spend long periods of time in vehicles such as professional drivers.”

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A research paper outlining the findings is published in Science of the Total Environment. In this study, the researchers tested NO2 in ten different vehicles, ranging in size and type (petrol, diesel, hybrid and electric were all included). Air quality measurements inside the vehicles were taken with a range of ventilation conditions, such as AC turned on or off and windows either closed or partially open.

Each vehicle was tested three times, firstly with its original air filter in place, then with a pollen filter, and lastly with the activated charcoal filter.

The researchers found that overall, in-vehicle NO2 concentrations were on average 1.6 times lower when the windows were closed and the ventilation system recirculated air, compared to levels when the windows were open. When new standard pollen filters were fitted, NO2 concentrations were almost unchanged between closed windows and fresh air coming through the ventilation system and with windows open.

However, with activated carbon filters fitted, in-vehicle NO2 levels were on average 14.3 times lower with closed windows and recirculated air. Even with fresh air coming through the ventilation system, NO2 levels were 6.6 times lower than levels with windows open. Maintaining appropriate ventilation is also important to prevent drowsiness, the team added.

Professor William Bloss, co-author on the paper, said: “These results show a fairly simple way to improve air quality inside vehicles, although as the main source of NO2 in our cities is diesel vehicles, reducing traffic emissions overall will bring the greatest air quality benefit across the general population.”