In: Civil Engineering
a.PM2.5 is a criteria pollutant that can have immense impact to our health and visibility. It is defined using the aerodynamic diameter. But how is this diameter being defined, i.e. what is the definition of aerodynamic diameter?
b. Why is PM2.5 defined using aerodynamic diameter?
c. What is the physical meaning of relaxation time of an atmospheric particle? And explain how the relaxation time is associated with the size of the particles.
d. Impactor and cyclone are commonly used size-selection devices to separate PM2.5 particles from the particle-laden air. Describe with sketches by hands to illustrate how the separation is achieved with the impactor. Please define relaxation time and explain how the particles separated with an impactor using the relaxation time concept. Be reminded to label the sketches clearly.
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