Some amount of dichloromethane $\left({\mathrm{CH}}_2{\mathrm{Cl}}_2\right)$  is added to 671.141 ml of chloroform $\left({\mathrm{CHCl}}_3\right)$  to prepare $2.6\times {10}^{-3}\mathrm{M}$ solution of ${\mathrm{CH}}_2{\mathrm{Cl}}_2$ (DCM). The concentration of DCM is ____________ppm
 (by mass) Given :
 Atomic mass: C = 12 H = 1
 Cl = 35.5 Density of   = 1.49 g cm^-3