A low-cost charcoal air filter can decrease nitrogen dioxide (NO2) levels inside vehicles by up to 90% in comparison to levels outside the vehicle.
According to research presented in a report by WM Air, the West Midlands Air Quality Improvement Programme at the University of Birmingham, charcoal filters, which cost between £10 and £20, can effectively remove NO2 from vehicle cabin air.
NO2 is a prevalent air pollutant that can worsen asthma and raise the risk of respiratory infections. Because traffic emissions are a major source of NO2, road users inside vehicles are exposed as air circulates from outside through open windows and ventilation systems.
While ventilation systems currently filter air, it is usually through a pollen filter. These keep tiny particles and pollen out of the vehicle, but they have little impact on gases like NO2. In contrast, activated carbon filters eliminate NO2 through a process known as adsorption, in which NO2 reacts with the carbon and sticks to the surface area of the filter.
The carbon filter, like the pollen filter, loses effectiveness over time, so it should be replaced on a regular basis 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. 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.
Dr. Vasileios Matthaios, Lead Researcher, University of Birmingham
The findings are summarized in a research paper in Science of the Total Environment. The researchers tested NO2 in 10 different vehicles ranging in size and type for this research (diesel, petrol, hybrid, and electric were all included). Air quality measurements were taken inside the vehicles under various ventilation conditions (AC turned on or off and windows either closed or partially open).
Each vehicle was tested three times: once with its original air filter, once with a pollen filter, and finally with the activated charcoal filter.
The scientists determined that when the windows were closed and the ventilation system recirculated air, in-vehicle NO2 concentrations were 1.6 times lower than when the windows were open.
When new standard pollen filters were installed, NO2 concentrations remained nearly constant between closed windows and fresh air coming through the ventilation system, as well as when the windows were open.
In-vehicle NO2 levels were 14.3 times lower with closed windows and recirculated air when activated carbon filters were installed. Even with the ventilation system providing fresh air, NO2 levels were 6.6 times lower than when the windows were open. Sustaining proper ventilation is also important for avoiding drowsiness.
These results show a fairly simple way to improve air quality inside vehicles, although as the main source of NO2 is our cities is diesel vehicles, reducing traffic emissions overall will bring the greatest air quality benefit across the general population.
William Bloss, Professor, Study Co-Author, University of Birmingham
Matthaios, V. N., et al. (2023) NO2 levels inside vehicle cabins with pollen and activated carbon filters: A real world targeted intervention to estimate NO2 exposure reduction potential. Science of The Total Environment. doi.org/10.1016/j.scitotenv.2022.160395.