Chapter 2
Aerosol Dynamics
2.1 Introduction
Airborne particulate matter (PM) contains various chemical components and ranges in size from few nanometres to several hundred micrometres (Hinds, 1999). It is apparent that PM is not a single pollutant, and its mass includes a mixture of numerous pollutants distributed differently at different sizes. Particle size is an essential parameter that determines the chemical composition, optical properties, deposition of particles and inhalation in the human respiratory tract (RT) (Hinds, 1999; Friedlander, 2000; Seinfeld and Pandis, 2006; Lazaridis, 2011). Particle size is specified by the particle diameter, 
, which is most commonly expressed in micrometres. Particles represent a very small fraction, less than 0.0001%, of the total aerosol mass or volume (Drossinos and Housiadas, 2006). The gas phase mainly influences the particle flow through hydrodynamic forces.
Particles may be classified into a number of categories; based on their size, they can be categorized according to (i) their observed modal distribution, (ii) the 50% cut-off diameter of the measurement instrument or (iii) dosimetric variables that are related to human exposure to atmospheric concentrations. However, ...
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