# How to find the top level of the planetary boundary layer in WRF?

I am working on WRF_Chem, I would like to calculate the concentration of CO2 just in the Planetary boundary layer(I mean, I want to calculate CO2 from surface to top of PBL).in WRF How can I calculate the level of PBL. in WRF we have (PBLH: the height of PBL but it doesn't inform us what is the top level of PBL compare all level of the model?). my model has a 37vertical levels. If I Know the level of PBL, I will calculate the pressure weight of its level and calculate the contribution of PBL concentration. how can I find the concentration Of CO2 in PBL height considering the weight of PBL layer? thank you for all your guidance.

## 1 Answer

Well, the variable PBLH should tell you the PBL height. If you want the level that the PBL is, I suggest modifying the Registry.EM_COMMON file.

Perhaps I can refer you to WRF-Python to help you with your calculation. For example, wrf.interplevel might be the function to use to interpolate to the PBL height. If you interpolate to fractions of the PBL height, you could one of the integration methods to sum up the number of fractions of the PBL height and get the average concentration of $$\ce{CO2}$$ in the PBL (also, divide by the PBL height to actually get the average).

• thank you dear BarocliniCplusplus for your response. yes I would like to have and calculate the **column average of CO2**(summation of CO2) from surface to end of PBL height. can the program you have introduced me help me in this matter? Thank you very much indeed. – sara May 12 at 21:42
• Well, it can get you part way. Since it lets you interpolate to different heights, you can use any of the integration methods of your choice to integrate over the PBL height. For example, you can interpolate halfway and use the trapezoidal integration to get an estimate. – BarocliniCplusplus May 12 at 22:05