Need a heck of a lot more data...
Questions:
Is there really more soot in the air now than there was a hundred years ago? While all combustion creates CO2, not all combustion creates soot. The more modern the combustion system, the less soot created.
A hundred years ago. Lower population, fewer machines, but really, really dirty machines. I'd love to see a graph of manmade soot over that time.
I don't see any natural soot sources, like forest fires, mentioned. Are these a factor?
As Ed points out, the obvious solution, as with CO2, is nuclear power.