What are the upsides and downsides of high-efficiency tires, compared to high-performance tires? I'm not familiar with the terms, in spite of having bought tires several times.

high-efficiency tyres have less rolling resistance and as a result are usually made of a harder rubber. as a result they also have less grip but this is fine if you adjust your speeds to match the conditions appropriately. some of them have additives in the rubber to try and get some of the lost grip back.

Distiction: Winter tires are made of a softer rubber compound, to be more flexible in winter termperatures. These softer winter tires wear very rapidly in summer temperatures, and experience a drive may have if they fail to change out their winter tires to the summer seasonal tires.

Half by what metric?

Mass pm2.5 and pm10 emissions per vehicle-km.

That doesn't seem particularly relevant when some of the other things are highly poisonous?

Why would you focus on that when the review is talking about studies showing health impacts and only mentions tires once, explaining that general environmental dust becomes "road dust" when kicked up by tires?

That's a good point, but it might not be the whole story. It's possible that tailpipe emissions are worse for your health than small rubber particles from tires