$3.$ HOW WELL DOES YOUR AIR FILTER WORK?

The BlueairTM HEPA $($High Efficiency Particulate Arresting$)$ air filter is designed to remove

particles from indoor air. Calculate the particle removal efficiency given the following data

$($you may assume all particles are the same size$)$:

Particle mass concentration in the ambient room air: $2\backslash$mu g m$-3$

Particle mass concentration leaving the HEPA filter: $1$ ng m$-3$

Air flow rate through the HEPA filter: $6$ m$3$ min $-1$