1.2 million premature deaths, not outright deaths. These will be people about to die anyway who died slightly sooner than otherwise. Car crashes kill people 50 years ahead of schedule, not 1 year.

Weapons are defined by intent, not body count.

I think he meant the intent of the creator of the compound/item.

A gun is created to kill. A taser to incapacitate. A knife is created to cut/stab things - and since human flesh is highly cuttable substance even kitchen knives are considered weapons. A car is created to transport people but can be used to kill. Cars are not weapons because in their conception there is no intent to harm someone.

What about a rock? The same analogy holds true. Anything can be a weapon, its simply absurd to contend that intent matters.

There has to be intent in there someone. A gun is a weapon. A rock can be a weapon. A dangerous polluting factory may be criminally negligent and morally despicable, but it's not a weapon unless it was deliberately deployed to maximize exposure to a target group. (Which isn't out of the question, given human nature, but I haven't heard of any evidence for it happening yet.)

What if we replace the gun and bullet with a bottle rocket? Is it a weapon now?

That's kinda the point of the article. Not only does it purify contaminated air for the occupants, it actually reduces contaminants outside the car. Tesla is marketing this to locales with literally dangerous levels of smog.

It is not a bioweapon. It is chemical weapon. Quite the different beast.