Questions on the "O3_OTH" and "O3_BCO" tags in CMAQ/ISAM

CMAQ-ISAM
1

Hi,

I am currently working on a study using CMAQ/ISAM v5.4 to investigate the contributions to 8-hour ozone concentrations from various sources in specific regions. To achieve this, I have taken the following steps:

  1. Prepared all input data for MEGANv3.2 and activated CTM_BIOGEMIS_MG Y to enable in-line biogenic emissions with MEGAN.

  2. Explicitly tagged all emissions, including biogenic and lightning emissions using the control file setup:

TAG CLASSES |OZONE
….
TAG NAME |RG1
REGION(S) |REGION1
EMIS STREAM(S) |MIOG

TAG NAME |RG2
REGION(S) |REGION1
EMIS STREAM(S) |LGTN

While conducting the simulations, I came across an unexpected result. The “OTH” tag (O3_OTH), representing contributions from non-tagged emission streams and other processes in the model, appears to be about 6.72% and comparable to the contribution from biogenic emissions.

I have two questions that I would greatly appreciate your insights on:

  1. Does the “OTH” tag (O3_OTH) still include contributions from online biogenic emissions even after explicitly tagging them in the control file?

  2. Regarding the “O3_BCO” (contribution from boundary conditions) in the model, I have enabled potential vorticity at the top of the modeling domain. However, I am unsure if “O3_BCO” accounts for the top boundary contribution. If not, is the contribution of top boundary going to O3_OTH?

I look forward to your response and appreciate any additional references or resources you may have on this topic.

Thank you for your time and assistance.

Please also see 3 related posts for your references
post 1
post 2
post 3

2

Hi Feng,

The “OTH” tag also includes inline emissions streams. Check your model configuration to see if you have any of these not explicitly tagged. See the documentation for the details:

If you have potential vorticity enabled, this would go to the “OTH” tag unless you have that the “PVO3” tagclass defined. This was a later addition to the code and unfortunately not well documented. It is something we will address in the next update to the documentation.

Finally, there other considerations for the “OTH” tag, and these are explained to some extent in the documentation supplement here:

The bottom section of this document provides some details about interactions between tags. Some of the mass tracked through these interactions does end up in the “OTH” tag. So, it is essentially impossible to make this tag strictly zero.

Sergey

3

Sergey,

Thank you for your prompt response. Before delving into the Description of the ISAM Chemistry Method from the document you provided, I have a preliminary question.

In the control file, I already have tagged biogenic emissions using MIOG, which serves as default for MEGAN. There should be a risk of double-counting the biogenic emissions if the “OTH” tag includes inline biogenic emissions streams as you mentioned. However, after analyzing the SA_ACOUN result at one monitoring site, it appears that this is not the case. The total of all tagged sources, including “OTH”, “BCO”, and “ICO”, aligns with the modeled value (please refer to the attached table below for further details). That indicates “OTH” should not include contribution from biogenic emissions, am I right? Thank you.

unit: ppb

obs mod AREA NONRAD ONROAD EGU NONEGU OILGAS AIRPORT MIOG FIRE3D LGTN O3_OTH O3_BCO O3_ICO Total
71.16 72.57 4.73 7.57 16.29 1.63 0.61 0.10 4.25 6.53 0.04 1.10 2.37 27.35 0.00 72.57
4

OTH tag only includes MIOG emissions if you didn’t specifically request a tag for them. There should never be double counting. It would include potential vorticity impacts in your case, because I don’t see a tag for that.

Sergey