CHIMERE model has days when PM2.5 is bigger then PM10

Hello,

I am using regional reanalysis data from CAMS European air quality forecasts. To be precise, I am using data from CHIMERE model. During my research , I found out that in some area (e.g. the point whose coordinates are 44.7N and 19W) there are days when PM2.5 is bigger then PM10 (e.g. some days between 15th November and 26th December 2019.) . Can you please explain me why does this happen?


Thank you in advance.