In a bid to highlight the clean air advantage of the Toyota Mirai, a hydrogen fuel cell electric car, the company is putting up pollution-scrubbing billboards.

Although the dominant type of energy storage in today’s electric cars is lithium-ion batteries, not every car company is going in that direction, as Toyota demonstrates with its continued push for a different technology — hydrogen fuel cells. Once lauded as the future of clean transportation and energy storage in a variety of other applications, hydrogen-based fuel cell systems have a great many barriers to adoption, one of which is lack of hydrogen infrastructure, and the other is the need to develop hydrogen production sources that aren’t fossil fuel-based or that require more energy to produce than can be released in the fuel cell.

But that hasn’t stopped Toyota from moving along with its hydrogen fuel cell Mirai sedan, and one advertising angle being used to boost the brand’s green credibility is a forthcoming billboard campaign in and around Los Angeles and San Francisco, California.

A series of 37 "eco-billboards" touting the fact that the Mirai’s "only emission is water" (at least at the proverbial tailpipe, as there are definitely emissions other than water associated with hydrogen fuel cells and any new car) will be installed with Clear Channel Outdoor Americas, and these billboards are said to remove nitrogen oxides (NOx) from the air. NOx, which are produced by combustion, such as in fossil fuel vehicles, is one of the key components of both smog and acid rain, and the billboards are said to "reverse the equivalent of 5,285 vehicles" worth of NOx emissions per month.

Although the billboards are still made from vinyl, as most billboards are, they are coated with a titanium dioxide layer developed by PURETi Group which is said to act like an air purifier or "catalytic converter," at least of the NOx in the surrounding air.

"When oxygen reacts with the energized titanium dioxide catalyst, NOx is converted to nitrate and removed from the air. The light-activated, smog-reducing billboards continue to purify the air as long as light, humidity, airflow and the titanium dioxide coating are present." – Toyota

The 37 billboards will total "24,960 square feet of pollution scrubbing surface," but will only be up from April 3rd through May 28th, so while it’s a cool idea, the actual impact of the campaign will probably be minimal at best.