You'd probably need SCUBA to keep out carbon monoxide. A dust mask is hard to breathe thru because you have a small surface area that you have to force the air thru. A respirator has a "fractal-like" filter that gives the filter a much larger surface area.
Speaking as a SCUBA diver, the equipment is not designed to handle high airflow (such as you need when working hard on a bicycle), so even if the air tank itself wasn't a problem you'd need, at a minimum, a heavily-adjusted second-stage (the one with the mouthpiece) regulator. Possibly a different regulator set altogether. On the other hand, one of the design considerations of a second-stage reg is that the purge valve needs to resist water pressure, including the pressure of swimming; air would generally not have that problem (and you probably wouldn't ha...
A 2006 study showed that “280,000 people in the U.S. receive a motor vehicle induced traumatic brain injury every year” so you would think that wearing a helmet while driving would be commonplace. Race car drivers wear helmets. But since almost no one wears a helmet while driving a regular car, you probably fear that if you wore one you would look silly, attract the notice of the police for driving while weird, or the attention of another driver who took your safety attire as a challenge. (Car drivers are more likely to hit bicyclists who wear helmets.)
The $30+shipping Crasche hat is designed for people who should wear a helmet but don’t. It looks like a ski cap, but contains concealed lightweight protective material. People who have signed up for cryonics, such as myself, would get an especially high expected benefit from using a driving helmet because we very much want our brains to “survive” even a “fatal” crash. I have been using a Crasche hat for about a week.