Near-zero SOA in wrfout (WRF-Chem v4.5.2 with chem_opt = 202)

[1 Zephy]

Hi all,

I am running WRF-Chem v4.5.2 with chem_opt = 202 (MOZART–MOSAIC, 4-bin). I am investigating aerosol–climate effects from anthropogenic emissions and biomass-burning (fire) emissions, but I am seeing extremely small SOA-related aerosol concentrations in the output (order ~1e−16), and in some cases essentially zero.

What I see:

• In wrfout, VBS aerosol-phase SOA species (e.g., asoa_a01–a04, bsoaa01–a04, and glysoa*_a01–a04) are ~1e−16 or ~0, with spatial structure but unrealistic magnitude.
• Condensable vapor variables (e.g., cvasoa*, cvbsoa*) are also ~0.
• Gas-phase VOC tracers such as BIGENE/BIGALK/ISOP are not zero in wrfout.
• My emission/species mapping appears correct (I can confirm the required MOZART species are present in wrfchemi_00z_d01; e.g., E_BIGENE, E_BIGALK, E_ISOP, E_TOLUENE, E_BENZENE, etc.). Boundary/IC mapping also appears consistent.

Questions:

1. Are there known configuration pitfalls in v4.5.2 that can lead to SOA being effectively shut off (e.g., chemistry options, aerosol options, emission switches, or compilation/config flags)?
2. which key intermediate variables or budget terms should I check?
3. if SOA is near-zero in this setup, how much could that bias aerosol–radiation/indirect effects when estimating climate impacts of anthropogenic + fire emissions? In other words, is it acceptable to proceed if my focus is climate response, or should I treat this as a critical issue requiring correction?

Environment:

• WRF-Chem: v4.5.2
• chem_opt: 202 (MOZART–MOSAIC 4-bin)
• Emissions: anthropogenic + biomass burning (wrfchemi / wrffirechemi); MOZART gas-phase species present in wrfchemi
• Output: BIGENE/BIGALK/ISOP non-zero; SOA aerosol-phase species ~1e−16; cvasoa/cvbsoa ~0

Any suggestions on the most likely causes and the best debugging steps would be greatly appreciated. If needed, I can share specific namelist options and a list of SOA-related variables present in my wrfout.

Thanks!

 

[Mary Barth]

Hi there,

I wonder if aerchem_onoff = 0 in your namelist. It should be = 1.

Mary 

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Mary Barth 

Senior Scientist   

phone: 303-497-8186    email: bar...@ucar.edu

NSF - National Center for Atmospheric Research

P.O. Box 3000

Boulder, CO 80307

Staff web page

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MUSICA Web Site

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[1 Zephy]

Hi Mary,

Thanks for the suggestion. In my namelist, aerchem_onoff is already set to 1 (see &chem below), and other chemistry switches are on as well (gaschem_onoff=1, wetscav_onoff=1, etc.). However, SOA-related aerosol variables (asoa/bsoa/glysoa*** in MOSAIC bins) remain ~1e−16 (or ~0) and cvasoa/cvbsoa** are also ~0, while other species look normal with reasonable output (BC, OC, BIGENE, BIGALK, ISOPR).

Do you have other recommended switches/diagnostics to check to confirm SOA/VBS production is active (or common pitfalls in v4.5.2 for chem_opt=202)?