8 is not 50% of 12. But we're talking about massive numbers here. If that "100" is 1,000,000 tons of soot, reducing human-produced soot from 12 to 8 is taking 40,000 tons of soot out of the environment. And that's likely not uniformly distributed across the country: you're far more likely to have hot spots of human-produced soot, which adds up to tens of thousands of kids who don't end up getting (or are affected less by) asthma, thousands of adults whose lifespans are materially lengthened, and greatly reduced healthcare costs.