SOAS emission in OFFLINE_BIOGENICVOC

[YanshunLi-washu]

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Yanshun Li

Your affiliation

Washu

Please provide a clear and concise description of your question or discussion topic.

Hi Support Team,

I notice that in the OFFLINE_BIOGENICVOC section of HEMCO_Config.rc, there are SOAS emission scaled from precursors:

...
0 BIOGENIC_ISOP_SOAP -                                                                                                            -             -                     -   -  -       SOAP 610 4 2
0 BIOGENIC_ISOP_SOAS -                                                                                                            -             -                     -   -  -       SOAS 610 4 2
...
0 BIOGENIC_LIMO_SOAP -                                                                                                            -             -                     -   -  -       SOAP 611 4 2
0 BIOGENIC_LIMO_SOAS -                                                                                                            -             -                     -   -  -       SOAS 611 4 2
...
0 BIOGENIC_MTPA_SOAP -                                                                                                            -             -                     -   -  -       SOAP 611 4 2
0 BIOGENIC_MTPA_SOAS -                                                                                                            -             -                     -   -  -       SOAS 611 4 2
...
0 BIOGENIC_MTPO_SOAP -                                                                                                            -             -                     -   -  -       SOAP 611 4 2
0 BIOGENIC_MTPO_SOAS -                                                                                                            -             -                     -   -  -       SOAS 611 4 2
...
0 BIOGENIC_SESQ_SOAP -                                                                                                            -             -                     -   -  -       SOAP 612 4 2
0 BIOGENIC_SESQ_SOAS -                                                                                                            -             -                     -   -  -       SOAS 612 4 2

Have two questions:
(1) I thought the formation of SOAS should be 100% during chemistry, why we put it into the HEMCO emission module? Feel free to correct me if my understanding is wrong.
(2) Why the scaling factors for SOAP & SOAS are the same?

Thanks,
Yanshun

[yantosca]

Thanks for writing @YanshunLi-washu. I'm tagging the co-chairs of the Emissions WG who may be able to provide more information than I can: @eamarais @jaegle [email protected]

[eamarais]

Hi @YanshunLi-washu, these are fixed mass yields for biogenic VOCs for the simple SOA scheme. These are applied in HEMCO_Config.rc, as these fixed mass yields are tied to emissions.
In version 14.1.0, the SOA mass yields are 3% for isoprene and 10% for the other biogenic VOCs distributed equally between SOAP and SOAS. GEOS-Chem includes an aging lifetime for SOAP to convert to SOAS. This I think is still dealt with in carbon_mod.F90.

[YanshunLi-washu]

Hi @eamarais , thanks a lot for these info! So the mass yields of SOA from isoprene and other VOCs are actually chemical process and we put it in the HEMCO module just for easy implementation? Or do we really have primary SOAS emissions?

[eamarais]

Hi @YanshunLi-washu, these mass yields are in HEMCO because these are tied to the emissions and HEMCO is the emissions processing package for GEOS-Chem. As stated in Pai et al. (https://acp.copernicus.org/articles/20/2637/2020/acp-20-2637-2020.pdf), the simple scheme assumes 50% of the SOA (SOAS) is formed promptly (soon after emission) and the other 50% (SOAP) evolves gradually to SOAS with a lifetime of a day.

[YanshunLi-washu]

Got it @eamarais Thank you so much for the explanation and recommending the paper! Just further curious about the relationship between VOCs and SOAP. Is SOAP some special category of VOC that will form SOA through aging?

[eamarais]

@YanshunLi-washu, I'd be hesitant to categorise SOAP as a special VOC, as we don't include it in the VOC budget and doing so might lead to oddities like double counting. It's a simple way to represent the delayed formation of SOA from VOC precursors that might undergo reactions that yield higher molecular weight, lower volatility compounds that are ideal SOA precursors.

[YanshunLi-washu]

Thanks @eamarais for the explanation. It's really helpful!