I have downloaded the pm10 and pm2.5 forecast data from CAMS real-time archive, but the value are all 0.
Step 0 indicates analysis, not forecast. In the current model setup, pm10 and pm2.5 are not computed at analysis time (Step 0), so zeros are stored instead.
Note that these fields are all instantaneous rather than time-averaged.
This issue has been fixed for data starting from September 2017.