# BCO tag in CMAQ-ISAM **URL:** \ **Category:** CMAQ-ISAM\ **Created:** [November 30, 2024, 2:03pm UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396 "2024-11-30T14:03:47Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![lotso](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@lotso](https://forum.cmascenter.org/u/lotso)\ **Post date:** [November 30, 2024, 2:03pm UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396/1 "2024-11-30T14:03:47Z")
I simulated two scenarios with CMAQ-ISAM respectively, and the main difference between the two scenarios is the emission inventory. The BASE scenario includes emissions from anthropogenic sources and natural sources, while the Background scenario only includes emissions from natural sources. Comparing the ISAM results of the two scenarios, it is found that the contribution of BCON changes. Is this normal? (The same BCON file is used for both scenarios) ![image](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/8/87990406b88cde57f3807d7af014e43b7c04cb98.png) ---
**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:** [November 30, 2024, 7:57pm UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396/2 "2024-11-30T19:57:01Z")
Hello lotso, yes, the results of the BCO tag (or other tags) can change between simulations if the number and/or definition of tags differs between simulations, even if the definition of the tag in question (like BCO) does not change between simulations. This is discussed on pages 4 - 7 of the [ISAM chemistry supplement](https://github.com/USEPA/CMAQ/blob/main/DOCS/Users_Guide/Supplement/CMAQ_ISAM_Chemistry_Supplemental_Equations.pdf) linked from the [ISAM chapter of the users guide](https://github.com/USEPA/CMAQ/blob/main/DOCS/Users_Guide/CMAQ_UG_ch11_ISAM.md). This ISAM behavior was also discussed in posts 11 - 13 of this [earlier thread](https://forum.cmascenter.org/t/sensitivity-of-boun-and-pvo-in-cmaq-ddm/4298/11). Christian ---
**Author:** ![lotso](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@lotso](https://forum.cmascenter.org/u/lotso)\ **Post date:** [December 5, 2024, 2:26am UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396/3 "2024-12-05T02:26:16Z")
Hello Christian, Thank you very much for your answer. I would also like to ask why the value of O3 \_ ICO is so large in my ISAM results (the spatial distribution of O3 \_ ICO for both scenarios is shown in the figure)? How can I modify it? ![image](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/f/fe904cb4a230ca79bf0af6c973b0fe02adc49dee.png) Lotso ---
**Author:** ![whr](https://avatars.discourse-cdn.com/v4/letter/w/22d042/32.png) [@whr](https://forum.cmascenter.org/u/whr)\ **Post date:** [December 5, 2024, 3:12am UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396/4 "2024-12-05T03:12:35Z")
Hello Lotso, What is your spin-up time? If the spin-up time is not long enough, it is likely that the contribution from the ICO will be high. Haorui Wang ---
**Author:** ![lotso](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@lotso](https://forum.cmascenter.org/u/lotso)\ **Post date:** [December 5, 2024, 4:31am UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396/5 "2024-12-05T04:31:34Z")
Hello whr, My spin-up time is 8 days. Lotso ---
**Author:** ![whr](https://avatars.discourse-cdn.com/v4/letter/w/22d042/32.png) [@whr](https://forum.cmascenter.org/u/whr)\ **Post date:** [December 5, 2024, 5:18am UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396/6 "2024-12-05T05:18:18Z")
Hello Lotso, I have done several long-term simulations in the Asian domain using CMAQ-ISAM, which may be helpful to you. Can you share your email address? I will contact you to get more details. Haorui Wang ---
**Author:** ![lotso](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@lotso](https://forum.cmascenter.org/u/lotso)\ **Post date:** [December 5, 2024, 6:49am UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396/7 "2024-12-05T06:49:55Z")
Hello Haorui Wang, My email address is [kongzh1@126.com](mailto:kongzh1@126.com). Thank you for your share! Lotso ---
**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:** [December 5, 2024, 12:30pm UTC](https://forum.cmascenter.org/t/bco-tag-in-cmaq-isam/5396/8 "2024-12-05T12:30:55Z")
A spin-up period of 8 days is indeed on the short side for simulations that span a large geographical area like yours. As @whr noted, a longer spin-up period will reduce the magnitude of the ISAM ICO tag. The exact length of the spin-up period will depend on domain size, season, and meteorological conditions. In some annual ISAM applications our group performed over the entire US, using a spin-up period of 1 month (starting on December 1 for an analysis period starting on January 1) was sufficient to reduce the ISAM O3\_ICO tag to \<= 1ppb throughout the domain.