The concentration of Sulfur Dioxide $(SO_2)$ in ambient atmosphere was measured as $30 \: \mu g /m^3$. Under the same conditions, the above $SO_2$ concentration expressed in ppm is _________.

Given: $P/(RT) = 41.6 \: mol/m^3$; where, $P=$ Pressure; $T=$ Temperature; $R=$ universal gas constant; Molecular weight of $SO_2 =64$.