Some amount of dichloromethane \( (\mathrm{CH_2Cl_2}) \) is added to \( 671.141 \, \text{mL} \) of chloroform \( (\mathrm{CHCl_3}) \) to prepare \( 2.6 \times 10^{-3} \, \text{M} \) solution of \( \mathrm{CH_2Cl_2} \) (DCM). The concentration of DCM is ________ ppm (by mass). [Given : Atomic mass : \( \mathrm{C} = 12 \), \( \mathrm{H} = 1 \), \( \mathrm{Cl} = 35.5 \) density of \( \mathrm{CHCl_3} = 1.49 \, \text{g cm}^{-3} \)]