A filter bag system is used to remove lead $(Pb)$ particulate matter from a gas stream. A $7\frac{m^3}{m}in$ inlet stream $(320K,1$atm$)$ contains $1\mathrm{.}5\frac{ug}{\text{a}\text{c}\text{m}}$ of $Pb.$ Find the required removal efficiency if the cleaned outlet stream must contain no more $Pb$ than $100ppt[$parts per trillion $(1$ in ${10}^{12}].$

The molecular weight of $Pb$ is $207\frac{g}{\text{m}\text{o}\text{l}}$