I am running CMAQv5.5 with the Process Analysis ¶ module enabled. I am analyzing the output for a single grid cell, and I find that the following cloud‑related process variables (CLDS_ASO4I, CLDS_ASO4J, CLDS_O3, CLDS_HNO3) are exactly zero for every output time step over a period of more than 700 hours.
I would expect these terms to show at least some temporal variability (positive or negative) because cloud processes – including aqueous‑phase chemistry, scavenging, and mixing – are typically active.The sulfur tracking module (STM) indicates that I have enabled liquid-phase reactions in cloud water. Even if the net effect were occasionally zero, it seems highly improbable that they remain strictly zero over such a long simulation period. I have no idea where the problem lies.
A few questions may help us understand and diagnose this issue:
What mechanism are you using?
Are you using a CMAQ modeling platform that is readily available, ie one of the benchmark cases, to allow us to duplicate your observation?
In addition to using the Sulphur tracking model, are there any other non-default options selected? Please share your run script and build script, if possible.
Do you see the same results without the STM turned on?
Are you using the Budget tool for your analysis?
What does your Process Analysis Control file contain? It should be in the BLD directory and may be named pa_cb6r5_ae7_aq.ctl or pa_{mechanism}.ctl depending on what mechanism was selected.
Could the CLDS_xxx values be so small that the output is being rounded and reported as zero for that grid cell?
What does VERDI show for the other grid cells? Try setting a diverging pallete, and then create an animation of the tile plot for the CLDS_ASO4J variable.
Thank you very much for your kind assistance and thoughtful questions！
Mechanism: BLD_CCTM_v55_intel_cb6r3_ae7_aq_m3dry
Benchmark case? No – we simulated the Beijing area for December 2023–January 2024 using local inputs.
We used the official CMAQv5.5 run and build scripts. The run script run_cctm_Bench_2018_12NE3_CB6R5.csh was modified only for file paths.
Results are identical when STM is turned off.
Budget outputs are generated, but we have not yet analysed them in detail.
We modified it to define FAMILY ASO4 = ASO4J + ASO4I and set IPR_OUTPUT ASO4 = EMIS + CHEM + DDEP + CLDS + AERO + TRNM.
CLDS values appear extremely small. Retaining 7 decimal places reveals variations, and a summer simulation for Beijing shows clearly non‑zero CLD changes.
In summary, we attribute the zero CLDS outputs to very small contributions (likely due to limited cloud cover) that are rounded to zero at default precision. We truly appreciate your help in diagnosing this issue!
