Wrong values of PURB (percentage of urban area) in MCIP

Hi all,

When I compared my CCTM output with the observation, I find the O3 value is much higher than the observation data. I searched the previous discussion https://www.cmascenter.org/cmaq/documentation/4.6/ADVECTION_DIFFUSION.txt . From the .txt, I guess there might be some mistakes with the Kzmin setting. I checked my GRIDCRO2D file and found the values of PURB are either -9.999*e+36 or 0.

I also found the discussion about the PURB MCIP cannot generate PURB (percentage of urban area) . Compared with the discussion, the LANDUSEF values in my geo_em.d01.nc file are between 0 and 1, and I did use the correct geo_em.d01.nc in the mcip script.

My question is that are the values of PURB correct? If not, how can I correct it? Thanks in advance!


FWIW, the “-9.999e36” is “missing” (I/O API BADVAL3).

For the record, since REAL arithmetic has inherent round-off problems, the standard test that you may see in the code for missing is

`X < AMISS3 (== -9.0E36)`

Carlie J. Coats, Jr., Ph.D. cjcoats@email.unc.edu
Senior Software Engineer I/O API Author/Maintainer
Center for Environmental Modeling for Policy Development,
UNC Institute for the Environment www.ie.unc.edu
100 Europa Dr., Suite 490 Rm 4051 / Campus Box 1105 919.843.5951
Chapel Hill, NC 27599-1105 Fax 919.966.9920

Hi Carlie,

Thanks a lot! Do you have any idea how I can get a valid value for PURB?

I don’t know how MCIP does it, but when I’ve needed it, I’ve used the NLCD land cover as a starting point. (t’s on a 30meter-resolution Albers-projection grid), and when doing land surface modeling, I’ve taken that and averaged it over my modeling grid to get land cover fractions (much more accurate than going through some intermediate grid, but also more compute-intensive).

– Carlie

Hi Carlie,

Thank you for the information! I will have a try.


As @cjcoats pointed out, there is something wrong with your PURB values. PURB is the “percentage of urban area (based on land coverage)”, so the values should range between 0 and 100. The values in PURB are not going to be straight conversions of the fractions of urban area in the cell, so please proceed carefully if you want to do this independently.

Are you sure that you correctly added your geo_em.d01.nc file into your MCIP run? Please check your MCIP log file to see if you can find any additional information.