When manufacturers shout about how clean their cars are, you can usually find holes in their claims if you really start researching the topic. Remember when Toyota said its non-plug-in hybrids were self-charging hybrids and this infuriated car buyers and members of the press alike for being misleading marketing, well, the manufacturer is at it again... kind of.

This time it claims its new Mirai fuel-cell sports sedan is not only tailpipe emissions-free, but that it actually cleans the air as you drive it and it sounds preposterous at first glance. However, while it is just as blatant a marketing slogan as ‘ self-charging hybrids,’ there may actually be more truth behind it.

Now in order to understand why that is, you need to know how a hydrogen fuel-cell works. Basically, the fuel-cell requires air for the chemical reaction of splitting hydrogen atoms and that air is preferably clean and free of any unwanted particles and pollutants.

And in order to clean the air before it is used, the system runs it through a special dust filter that eliminates particles as small as PM2.5, then an electrostatic paper and fabric filter that removes any unwanted chemicals. The manufacturer even included a dedicated air purification screen in the Mirai’s infotainment

that shows the amount of air purified when driving through an easy-to-understand graphic of runners and digital display. It also includes an Air Purification meter that shows how much air is purified during acceleration. The meter enables the driver to feel the contribution that the new Mirai is making to the environment.

However, as is the case with such claims made by automakers, there is always a but. In this case the but has to do with the way hydrogen is produced - mostly through steam reforming natural gas, coal gasification, biomass gasification or oxidation of methane. All these methods use quite a bit of energy and they bring down the vehicle’s overall efficiency and emissions go up.

This discussion is very similar to the one about how the electricity that powers EVs is produced. Even though a BEV has no tailpipe emissions, if you burn coal to power it, this negates most if not all the benefit. The same can be said for the production of hydrogen - it may be the most abundant element in the universe, but it is certainly not that easy to separate into its pure form.

With all of this in mind, I think it’s fair to say this is not a misleading claim, but one that should be viewed in a broader context, keeping in mind where the hydrogen is sourced. Green Car Reports recently test drove the new Mirai, and after covering 1,351 miles, the car said it had cleaned 1,457 kiloliters (about 48,000 cubic feet) of air during the journey.

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