Question Regarding `force_use_old_data` and Emission Compatibility in WRF-Chem v4.6.0

Naser Mohammadzadeh

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Jun 26, 2026, 6:37:58 AM (12 days ago) Jun 26

to wrf-chem

Dear WRF-Chem Support Team,

I am currently running WRF-Chem v4.6.0. Previously, I successfully ran WRF-Chem v3.9.1. To migrate to v4.6.0, I updated several settings in my namelist.input.

One of the options I changed is:

force_use_old_data = .true.

Before enabling this option, I encountered an error when running WRF-Chem v4.6.0. After setting force_use_old_data = .true., the model ran successfully.

My main question is about the emission files. I generated my anthropogenic emissions using the EDGAR-HTAP emission preprocessor provided with older versions of WRF-Chem.

I would appreciate it if you could clarify the following:

Is the EDGAR-HTAP emission preprocessor intended only for WRF-Chem versions prior to v4?
Is there a different or updated method for generating emission files for WRF-Chem v4.6.0?
What exactly does force_use_old_data = .true. do? Does it simply allow WRF-Chem to read older-format emission files, or does it ignore certain compatibility checks or modify the way the emission data are processed?
Fundamentally, why do emission files generated for older WRF-Chem versions cause errors in v4.x? Were there changes in the emission file format or data structure?
I also noticed that the PM₂.₅ and PM₁₀ outputs are different between WRF-Chem v3.9.1 and v4.6.0, even though I am using the same model configuration and emission files. Could you please explain why these two versions produce different PM₂.₅ and PM₁₀ results? Are there any changes in the aerosol module, diagnostics, or PM calculation methods in WRF-Chem v4.6.0 that could account for these differences?

For reference, I have attached my namelist.input files for both WRF-Chem v3.9.1 and WRF-Chem v4.6.0.

I would greatly appreciate your guidance on these issues.

Thank you very much for your time and assistance.

Best regards,

Naser

TimeSeries_PM10_WRF460_MOZ_AAQ24_Anth24_YesMOZ_DEmiss_673hr_RMSE_MB_AAQ24.png

TimeSeries_PM25_WRF460_MOZ_AAQ24_Anth24_YesMOZ_DEmiss_673hr_RMSE_MB_AAQ24.png

TimeSeries_PM10_WRF391_MOZ_AAQ24_Anth24_YesMOZ_DEmiss_673hr_RMSE_MB_AAQ24.png

TimeSeries_PM25_WRF391_MOZ_AAQ24_Anth24_YesMOZ_DEmiss_673hr_RMSE_MB_AAQ24.png

namelist_3.9.1.input

namelist_4.6.0.input

Gabriele Pfister

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Jun 26, 2026, 10:44:46 AM (11 days ago) Jun 26

to naser.moham...@gmail.com, wrf-chem

Hello Naser,

since this forum only can handle requests related to our developments in WRF-Chem, please reach out with your question on force_use_old_data to the general WRF MPAS Forum. However, the answer is very simple. I assume you are using met data that were generated with WPS V3.9? If you have to tell later WRF-chem versions that your met input files come from an older WPS version.

As for the question on EDGAR-HTAP emission preprocessor provided with older versions of WRF-Chem - do you mean the anthro_emis preprocessor we provide on our website (and which should work with any WRF-Chem version) ? Or do you refer to some other tool? If you refer to any other tool, then we will not be able to help you.

Gabi

Naser Mohammadzadeh

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Jun 26, 2026, 8:32:26 PM (11 days ago) Jun 26

to Gabriele Pfister, wrf-chem

Hello dear Pfister

Thank you for your reply

You are right. I am using WPS 3.9.1 for WRF-chem 3.9.1 and WPS 4.6.0 for WRF-chem 4.6.0.

You mean if I use same WPS for both versions, result gets similar? And there is no diff in modules for calculation of PM10 and Pm2.5 in Mozcart?

About EDGAR-HTAP question, yes I am using your provided code for making emissions. I am using anthro_emis preprocessor on your website.