# How to calculate SOA concentration

**URL:** <https://forum.cmascenter.org/t/how-to-calculate-soa-concentration/5894>\
**Category:** CMAQ\
**Tags:** cmaq\
**Created:** [July 3, 2025, 2:20pm UTC](https://forum.cmascenter.org/t/how-to-calculate-soa-concentration/5894 "2025-07-03T14:20:14Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![wxy](https://avatars.discourse-cdn.com/v4/letter/w/eada6e/32.png) [@wxy](https://forum.cmascenter.org/u/wxy)\
**Post date:** [July 3, 2025, 2:20pm UTC](https://forum.cmascenter.org/t/how-to-calculate-soa-concentration/5894/1 "2025-07-03T14:20:14Z")

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Hello everyone,

I’m a new user of CMAQ. I really need some help. The version I am using is CMAQv5.5\_cb6r5\_ae7\_aq\_m3dry, and I want to calculate the total concentration of SOA. After running “Combine”, I obtained a variable named ASOMIJ. According to some previous posts on this forum, ASOMIJ represents the total concentration of SOA. Is my understanding correct? If so, the ASOMIJ value I calculated seems a bit too high. My simulation region is located in East Asia. According to some literature, the maximum SOA concentration in this region should be around 5 μg/m³, but my simulation results are approximately 10 times the normal value. I’m new to this and I don’t know what mistake I made. I would be grateful for any replies.

WXY  
2025.7.3

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**Author:** ![hogrefe.christian](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@hogrefe.christian](https://forum.cmascenter.org/u/hogrefe.christian)\
**Post date:** [July 7, 2025, 4:01pm UTC](https://forum.cmascenter.org/t/how-to-calculate-soa-concentration/5894/2 "2025-07-07T16:01:00Z")

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Hello @wxy ,

yes, the post-processed variable ASOMIJ represents total SOA.

You do not mention whether you enabled the formation of PCSOA in your DESID control namelist file, and if so, which sector(s) it was enabled for. If PCSOA was enabled and you want to investigate whether it played a substantial role in your higher-than-expected simulated ASOMIJ, you could try recalculating ASOMIJ without species APCSOJ. Please see the comments on PCSOA in the DESID control namelist file.

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**Author:** ![system](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/1X/9a72c78e529465c3f1053af404e3033b0875428c.png) [@system](https://forum.cmascenter.org/u/system)\
**Post date:** [July 14, 2025, 6:28pm UTC](https://forum.cmascenter.org/t/how-to-calculate-soa-concentration/5894/3 "2025-07-14T18:28:23Z")

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Closed on July 14, 2025, 6:28pm UTC

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