Do pollen/intake vehicle filters remove harmful exhaust fumes?

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Car Clinic: Do intake filters remove harmful exhaust particles from entering a vehicle's cabin

Q. I am worried about exhaust fumes from other vehicles entering the cabin of my BMW 3-series and Jaguar S-type. Will the pollen/intake filter remove at least some of the harmful particles?
JM, Orpington, London

A. The most common exhaust pollutants that damage health are oxides of nitrogen (NOx) and soot — both by-products of burning diesel. Modern engines’ emissions-control equipment, such as diesel particulate filters and catalytic convertors, intercept a lot of these harmful emissions but not all.

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Don’t panic, though. On both your cars — and indeed on most modern vehicles — the air that enters the cabin through the heater or air-conditioning first must pass through a very fine pollen filter. This extracts virtually all particles down to a diameter of 5 microns (five-millionths of a metre), and 80% of particles as small as 3 microns. As the soot that harms health is in the range of 2.5-25 microns the pollen filter will trap almost all these particles. In addition, charcoal granules will absorb noxious gases.

This assumes that your filters are up to scratch. They should be swapped each year or every 12,000-15,000 miles, so check with your garage to see when they were last renewed. You could change them yourself — new filters typically cost £15-£25. It is a simple DIY job on most BMW 3-series models but the S-type is trickier. On post-2004 cars it requires the removal of the windscreen wiper arms, so you might want a garage to do this.

Sunday Times Driving Car Clinic: Tim Shalcross, advance driving advice

Tim Shallcross used to train AA patrols to fix cars. Now he advises the Institute of Advanced Motoring – read more from Tim here.

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