The “physical laws” that regulate the diffusion and deposition of particles in the air

The here repor ted de nitions of few fundamental physical laws can help to understand the mechanism of particle behavior and consider the consequent air sampling difficulties. Brownian motion: As the par ticles migrate through a body of air, random impacts from individual molecules will cause them to veer from course. Drag coefficient: It is the ratio of the force of gravity to the iner tial force on a par ticle in uid. It indicates how a par ticle will resist any force that could cause a change in the par ticle velocity. Smaller par ticles have smaller drag coef cients due to their lesser masses.

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