50% number of particulates might not amount to 50% of the health risk.
Not all particles are the same. Diesel exhaust particulates are polycyclic aromatic hydrocarbons, i.e. pure carcinogen. Whereas I really doubt tire and brake dust has the same health risk "per particle".
Granted it may even be higher! But comparing two different things by simply "number of particles" isn't helpful.
Not all particles are the same. Diesel exhaust particulates are polycyclic aromatic hydrocarbons, i.e. pure carcinogen. Whereas I really doubt tire and brake dust has the same health risk "per particle".
Granted it may even be higher! But comparing two different things by simply "number of particles" isn't helpful.