2.3. PM from the vehicles
Different to the complex pathway of PM from coal-fired
combustors, particles from internal combustion engines are quite
simple and can be divided into solid and volatile particles. The
solid particles mainly consist of agglomerated carbonaceous
primary particles, which are usually described as soot. The volatile
nanoparticles are usually formed by nucleation of sulfuric acid,
water, and other species, which contribute not much. The two
different kinds of particles usually form separate modes in the
number size distribution, which are referred to as accumulation
mode and nucleation mode.