Little biogenic contributions to O3 in CMAQ-ISAM results

Hi all, I’m performing a simulation for Southern California. As I was checking my SA outputs, I found my biogenic contributions to O3 over Los Angeles is very small (less than 1%), which seems a little strange. I checked my biogenic emissions and they were read correctly by the CMAQ. As I believe Los Angeles is in VOC-limited regime for O3 production, the biogenic emissions should have some contributions to O3. Currently I’m performing sensitivity tests using brute-force methods. Before I get those results, I have some questions:

  1. Is there any way that I could know if a cell of my interest is VOC limited or NOx limited for O3 chemistry? For example, can I get a nc output telling the O3 production regime for all cells at different time? Or I could print the information in the log files.

  2. Is CMAQ-ISAM able to track gridded area emission sources? My biogenic emission files are gridded area emissions.Only 4 out of my 9 sources have both gridded area emissions and inline point emissions. My results indicate that 3 sources have contributions to O3 larger than 1%, and those 3 sources are among those 4 sources, which makes me wonder if that’s a coincidence.


Hi Yusheng,
I think I can answer your first question. As for identifying the ozone formation sensitivity in a specific grid cell of interest, you can run the IRR tool which incorporated in the PROCAN module. By using the ratio of H2O2/HNO3 calculated by the IRR, you can get the ozone formation sensitivity in a specific grid cell of interest (There are boundary values for VOCs limited and NOx limited). Another way to verify it is to use satellite products from OMI/TROPOMI etc. The indicator for satellite products is FNR (formaldehyde / NO2 values). You can activate the IRR easily in CMAQv5.3.1.
As for the low contribution of BVOC in ozone conc over LA, personally, I am not surprised about your results because the BVOC emission calculated by the MEGAN model is relatively low over LA which can be attributed to the low tree cover in urban regions of the megacity. To further illustrate the point, I attach the quick shot of BVOC emission over California FYI.
You are also welcome to directly reach out to me.