Preprints
https://doi.org/10.5194/egusphere-2025-2253
https://doi.org/10.5194/egusphere-2025-2253
05 Aug 2025
 | 05 Aug 2025

Simulated reductions in Heterogeneous Isoprene Epoxydiol Reactive Uptake from aerosol morphology in the contiguous United States using the Community Multiscale Air Quality Model (CMAQv5.3.2)

Sara L. Farrell, Quazi Z. Rasool, Havala O. T. Pye, Yue Zhang, Ying Li, Yuzhi Chen, Chi-Tsan Wang, Haofei Zhang, Ryan Schmedding, Manabu Shiraiwa, Jaime Greene, Sri H. Budisulistiorini, Jose L. Jimenez, Weiwei Hu, Jason D. Surratt, and William Vizuete

Abstract. Aerosol particles contain complex mixtures of polar and non-polar species that can undergo organic-inorganic phase separations. In phase-separated aerosol particles, the phase state of the outer organic coating can modulate heterogeneous chemistry. Heterogeneous chemistry leading to isoprene epoxydiol (IEPOX)-derived secondary organic aerosol (IEPOX-SOA) is encoded in the Community Multiscale Air Quality (CMAQ) model and has been the focus of previous aerosol phase separation and phase state work. In a previous study, a constant ratio of water in the organic coating (ws) was assumed in modeling phase separation and state. Recent studies, however, have highlighted ws as an important modulator of phase state. This work uses CMAQ version (version 5.3) with capabilities to model dynamic water uptake to the organic coating to better predict ws and its impact on the organic coating phase state. In addition, new parameterizations for estimating organic aerosol phase state were implemented in CMAQ, and the subsequent model predictions were used to compare their impacts on phase state and IEPOX-SOA predictions. These evaluations were completed simulating a summertime episode over the continental United States. Simulated diurnal profiles of aerosol phase state agreed within one standard deviation of observationally-derived field measurements. The implementation of phase separation and phase state parameterizations, on average, decreased IEPOX reactive uptake by up to 99.99 % compared to Base CMAQ, resulting in mixed model performance. While 2-methyltetrol performance improved with phase separation and phase state updates, methyltetrol sulfates and total IEPOX-SOA concentrations further underpredicted field observations in comparison to Base CMAQ.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics. The peer-review process was guided by an independent editor, and the authors also have no other competing interests to declare.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Journal article(s) based on this preprint

25 Sep 2026
Simulated reductions in heterogeneous isoprene epoxydiol reactive uptake from aerosol morphology in the contiguous United States using the Community Multiscale Air Quality Model (CMAQv5.3.2)
Sara L. Farrell, Quazi Z. Rasool, Havala O. T. Pye, Yue Zhang, Ying Li, Yuzhi Chen, Chi-Tsan Wang, Haofei Zhang, Ryan Schmedding, Manabu Shiraiwa, Jaime Green, Sri H. Budisulistiorini, Jose L. Jimenez, Weiwei Hu, Jason D. Surratt, and William Vizuete
Atmos. Chem. Phys., 26, 13557–13579, https://doi.org/10.5194/acp-26-13557-2026,https://doi.org/10.5194/acp-26-13557-2026, 2026
Short summary
Sara L. Farrell, Quazi Z. Rasool, Havala O. T. Pye, Yue Zhang, Ying Li, Yuzhi Chen, Chi-Tsan Wang, Haofei Zhang, Ryan Schmedding, Manabu Shiraiwa, Jaime Greene, Sri H. Budisulistiorini, Jose L. Jimenez, Weiwei Hu, Jason D. Surratt, and William Vizuete

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-2253', Anonymous Referee #1, 02 Sep 2025
    • AC2: 'Reply on RC1', Sara Louise Farrell, 13 Feb 2026
  • RC2: 'Comment on egusphere-2025-2253', Anonymous Referee #2, 06 Oct 2025
    • AC3: 'Reply on RC2', Sara Louise Farrell, 13 Feb 2026
  • RC3: 'Comment on egusphere-2025-2253', Anonymous Referee #3, 15 Oct 2025
    • AC1: 'Reply on RC3', Sara Louise Farrell, 13 Feb 2026

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Sara Louise Farrell on behalf of the Authors (13 Feb 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (18 Feb 2026) by Barbara Ervens
RR by Anonymous Referee #3 (20 Feb 2026)
RR by Anonymous Referee #1 (02 Mar 2026)
ED: Publish subject to minor revisions (review by editor) (02 Mar 2026) by Barbara Ervens
AR by Sara Louise Farrell on behalf of the Authors (12 Mar 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (13 Mar 2026) by Barbara Ervens
AR by Sara Louise Farrell on behalf of the Authors (07 Jun 2026)  Author's response   Manuscript 

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-2253', Anonymous Referee #1, 02 Sep 2025
    • AC2: 'Reply on RC1', Sara Louise Farrell, 13 Feb 2026
  • RC2: 'Comment on egusphere-2025-2253', Anonymous Referee #2, 06 Oct 2025
    • AC3: 'Reply on RC2', Sara Louise Farrell, 13 Feb 2026
  • RC3: 'Comment on egusphere-2025-2253', Anonymous Referee #3, 15 Oct 2025
    • AC1: 'Reply on RC3', Sara Louise Farrell, 13 Feb 2026

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Sara Louise Farrell on behalf of the Authors (13 Feb 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (18 Feb 2026) by Barbara Ervens
RR by Anonymous Referee #3 (20 Feb 2026)
RR by Anonymous Referee #1 (02 Mar 2026)
ED: Publish subject to minor revisions (review by editor) (02 Mar 2026) by Barbara Ervens
AR by Sara Louise Farrell on behalf of the Authors (12 Mar 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (13 Mar 2026) by Barbara Ervens
AR by Sara Louise Farrell on behalf of the Authors (07 Jun 2026)  Author's response   Manuscript 

Journal article(s) based on this preprint

25 Sep 2026
Simulated reductions in heterogeneous isoprene epoxydiol reactive uptake from aerosol morphology in the contiguous United States using the Community Multiscale Air Quality Model (CMAQv5.3.2)
Sara L. Farrell, Quazi Z. Rasool, Havala O. T. Pye, Yue Zhang, Ying Li, Yuzhi Chen, Chi-Tsan Wang, Haofei Zhang, Ryan Schmedding, Manabu Shiraiwa, Jaime Green, Sri H. Budisulistiorini, Jose L. Jimenez, Weiwei Hu, Jason D. Surratt, and William Vizuete
Atmos. Chem. Phys., 26, 13557–13579, https://doi.org/10.5194/acp-26-13557-2026,https://doi.org/10.5194/acp-26-13557-2026, 2026
Short summary
Sara L. Farrell, Quazi Z. Rasool, Havala O. T. Pye, Yue Zhang, Ying Li, Yuzhi Chen, Chi-Tsan Wang, Haofei Zhang, Ryan Schmedding, Manabu Shiraiwa, Jaime Greene, Sri H. Budisulistiorini, Jose L. Jimenez, Weiwei Hu, Jason D. Surratt, and William Vizuete
Sara L. Farrell, Quazi Z. Rasool, Havala O. T. Pye, Yue Zhang, Ying Li, Yuzhi Chen, Chi-Tsan Wang, Haofei Zhang, Ryan Schmedding, Manabu Shiraiwa, Jaime Greene, Sri H. Budisulistiorini, Jose L. Jimenez, Weiwei Hu, Jason D. Surratt, and William Vizuete

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Latest update: 09 Oct 2026
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Short summary
Fine particulate matter (PM2.5) has become increasingly important to regulate and model. In this study, we parameterize non-ideal aerosol mixing and phase state into the Community Multiscale Air Quality (CMAQ) model and analyze its impact on the formation of a globally important source of PM2.5, isoprene epoxydiol (IEPOX)-derived PM2.5. Incorporating these features furthers model bias in IEPOX-derived PM2.5, however, this work provides potential phase state bounds for future PM2.5 modeling work.
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