Inconsistency of sulfate emission estimation between STM and ISAM

Hi, friends

I am using CMAQ (5.3.3) to simulate the contribution of primary particulate sulfate to Shanghai over eastern China. I activated both the sulfur tracking method (STM) and integrated source apportionment method (ISAM) to track the primary sulfate species to the atmospheric sulfate concentration during the simulation. In the ISAM, I tracked sulfate emission contribution from 8 sources, including CBC, PPC, CEC, IRC, and 4 other sources. The simulation period is January 5 - January 31, 2019. Both the STM and ISAM results were averaged temperally.

Problem: I found that the sum of the particulate sulfate (4.08 μg/m3) from the CBC, PPC, CEC and IRC is greater than the sulfate emission (ASO4EMIS, 3.46 μg/m3) from STM over Shanghai. I am using the cb6r3_ae7_aq mechanism and more details are listed in the attached files. Any comment from you is appreciated!

run_cctm.txt (41.5 KB)
isam_control.txt (2.3 KB)
EmissCtrl_cb6r3_ae7_aq_nitrate.nml.txt (32.2 KB)

I am not sure the best way to help understand and diagnose this issue. Hopefully @sergey and @mathur.rohit will reply shortly.

In ISAM, the aerosol sulfate (ASO4) of tracked sources does not just include sulfate emissions but also includes how source’s other emissions such as SO2 produce sulfate via gas phase and cloud chemistry. This secondary component can cause the sulfate sum over ISAM’s tracked sources to exceed the ASO4EMIS from the sulfur tracked method. Note that both ISAM and STM account for ASO4 loss from its conversion to organosulfate. Check reaction HET_IEPOXOS in the cb6r3_ae7_aq mechanism.


@lizadams @bhutzell Thank you for your kind replies which point out my mistakes and solve the problem.