CAMS ozone mass mixing ratio partial column


I would like to create ozone partial column using the CAMS ozone mass mixing ratio parameter. I integrated over the pressure levels ( 800hPa-400hPa) and I would like to convert this in DU.
I guess that perhaps the correct procedure is to first convert the ozone MMR in mass concentration (kg/m3), then integrate, and then convert in DU.
Is this the correct procedure?
Thank you in advance!

Best regards,