Comprehensive isoprene and terpene gas-phase chemistry improves simulated surface ozone in the southeastern US

Schwantes, Rebecca H.; Emmons, L. K.; Barth, M. C.; Tyndall, G. S.; Hall, Samuel R.; Ullmann, Kirk; Clair, J. M. St; Blake, Donald R.; Wisthaler, Armin; Bui, T. P.

doi:10.5194/acp-20-3739-2020

Cited by 69 publications

(97 citation statements)

References 188 publications

(395 reference statements)

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“…Further improvement of the simulation of surface ozone will require simultaneous improvement of the emissions of ozone precursors (i.e, CO, hydrocarbons, and NO x ), the chemical mechanism for the oxidation of VOCs and NO x , and the representation of physical influences on ozone, such as dry deposition to land and ocean surfaces (e.g., Clifton et al, 2019). An expansion of the terpene oxidation chemistry has been developed (MOZART‐T2), which further improves the simulation of surface ozone particularly in forested regions (Schwantes et al, 2020). That work presents a detailed evaluation of the T1 and T2 mechanisms for the southeastern United States showing that the increased chemical complexity of T2 allows for reproduction of many observed oxidation products, as well as improving the simulation of surface ozone.…”

Section: Discussionmentioning

confidence: 99%

“…CESM provides flexibility in the chemical mechanism used in simulations, which can be readily modified by users. Future releases of CESM will include options for additional chemical mechanisms, such as a more comprehensive representation of terpene chemistry (Schwantes et al, 2020). A detailed mechanism of very short lived halogens has also been developed for CESM (Fernandez et al, 2019) and will be released in a future version.…”

Section: Discussionmentioning

confidence: 99%

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The Chemistry Mechanism in the Community Earth System Model Version 2 (CESM2)

Emmons

Schwantes

Orlando

et al. 2020

J Adv Model Earth Syst

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287

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The Community Earth System Model version 2 (CESM2) includes a detailed representation of chemistry throughout the atmosphere in the Community Atmosphere Model with chemistry and Whole Atmosphere Community Climate Model configurations. These model configurations use the Model for Ozone and Related chemical Tracers (MOZART) family of chemical mechanisms, covering the troposphere, stratosphere, mesosphere, and lower thermosphere. The new MOZART tropospheric chemistry scheme (T1) has a number of updates over the previous version (MOZART-4) in CESM, including improvements to the oxidation of isoprene and terpenes, organic nitrate speciation, and aromatic speciation and oxidation and thus improved representation of ozone and secondary organic aerosol precursors. An evaluation of the present-day simulations of CESM2 being provided for Climate Model Intercomparison Project round 6 (CMIP6) is presented. These simulations, using the anthropogenic and biomass burning emissions from the inventories specified for CMIP6, as well as online calculation of emissions of biogenic compounds, lightning NO, dust, and sea salt, indicate an underestimate of anthropogenic emissions of a variety of compounds, including carbon monoxide and hydrocarbons. The simulation of surface ozone in the southeast United States is improved over previous model versions, largely due to the improved representation of reactive nitrogen and organic nitrate compounds resulting in a lower ozone production rate than in CESM1 but still overestimates observations in summer. The simulation of tropospheric ozone agrees well with ozonesonde observations in many parts of the globe. The comparison of NO x and PAN to aircraft observations indicates the model simulates the nitrogen budget well.Plain Language Summary The set of chemical reactions for tropospheric chemistry used in the Community Earth System Model version 2 (CESM2) has been updated significantly over CESM1 in the Community Atmosphere Model with chemistry (CAM-chem) and Whole Atmosphere Community Climate Model (WACCM) configurations. The emissions used for the CESM2 simulations are documented here, with anthropogenic and biomass burning emissions based on the specified inventories for Climate Model Intercomparison Project 6 (CMIP6), and emissions of biogenic compounds, lightning NO, dust, and sea salt are calculated online and dependent on the simulated meteorology. Evaluation of the CAM-chem and WACCM configurations of CESM2 with observations indicate an underestimate of anthropogenic emissions of a variety of compounds, including carbon monoxide and hydrocarbons. The updated chemistry leads to an improvement in the simulation of tropospheric ozone.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The Chemistry Mechanism in the Community Earth System Model Version 2 (CESM2)

Emmons

Schwantes

Orlando

et al. 2020

J Adv Model Earth Syst

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287

169

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“…The reaction rate constant of isoprene + OH reaction matches the isoprene gas-phase reaction (Schwantes et al, 2020) . Similar high NOx yields for SOA formed from terpenes, benzene, toluene and…”

Section: No X -Dependent Yield Of Vbs Schemementioning

confidence: 57%

“…Because the isoprene SOA yield strongly depends on the gas-phase chemistry, we used the MOZART-TS2 (Model of Ozone And Related chemical Tracers, Troposphere-Stratosphere V2) detailed isoprene chemical mechanism recently developed by Schwantes et al (2020) . The MOZART-TS2 chemical mechanism includes more comprehensive and updated both isoprene and terpene chemistry, but for computational efficiency, we only implemented the new isoprene chemistry.…”

Section: Gas-phase Chemistry Of Isoprenementioning

confidence: 99%

Future changes in isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) under the shared socioeconomic pathways: the importance of explicit chemistry

Hodžić

Emmons

et al. 2020

Preprint

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Abstract. Secondary organic aerosol (SOA) is a dominant contributor of fine particulate matter in the atmosphere, but the complexity of SOA formation chemistry hinders the accurate representation of SOA in models. Volatility-based SOA parameterizations have been adopted in many recent chemistry modeling studies and have shown a reasonable performance compared to observations. However, assumptions made in these empirical parameterizations can lead to substantial errors when applied to future climatic conditions as they do not include the mechanistic understanding of processes but are rather fitted to laboratory studies of SOA formation. This is particularly the case for SOA derived from isoprene epoxydiols (IEPOX-SOA), for which we have a higher level of understanding of the fundamental processes than is currently parameterized in most models. We predict future SOA concentrations using an explicit mechanism, and compare the predictions with the empirical parameterization based on the volatility basis set (VBS) approach. We then use the Community Earth System Model 2 (CESM2.1.0) with detailed isoprene chemistry and reactive uptake processes for the middle and end of the 21st century under four Shared Socioeconomic Pathways (SSPs): SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5. With the explicit chemical mechanism, we find that IEPOX-SOA is predicted to increase on average under all future SSP scenarios, however with some variability in the results depending on regions and the scenario chosen. Isoprene emission is the main driver of IEPOX-SOA changes in the future climate, but IEPOX-SOA yield from isoprene emission also changes by up to 50 % depending on the SSP scenario, in particular due to different sulfur emissions. We conduct sensitivity simulations with and without CO2 inhibition of isoprene emissions that is highly uncertain, which results in a factor of two differences in the predicted IEPOX-SOA global burden, especially for the high-CO2 scenarios (SSP3-7.0 and SSP5-8.5). Aerosol pH also plays a critical role in the IEPOX-SOA formation rate, requiring accurate calculation of aerosol pH in chemistry models. On the other hand, isoprene SOA calculated with the VBS scheme predicts nearly constant SOA yield from isoprene emission across all SSP scenarios, as a result, it mostly follows isoprene emissions regardless of region and scenario. This is because the VBS scheme does not consider heterogeneous chemistry, in other words, there is no dependency on aerosol properties. The discrepancy between the explicit mechanism and VBS parameterization in this study is likely to occur for other SOA components as well, which may also have dependencies that cannot be captured by VBS parameterizations. This study highlights the need for more explicit chemistry, or for parameterizations that capture the dependence on key physico-chemical drivers when predicting SOA concentrations for climate studies.

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“…We used the default setting to conduct the simulations as a basis for estimating the different mixing state indices with the corresponding emulator in each grid cell. However, it should be noted that limitations and systematic biases in CESM (Hodzic et al., 2020; Schwantes et al., 2020) may be translated into the mixing state estimates.…”

Section: Partmc‐mosaic Emulator Development and Applicationmentioning

confidence: 99%

Estimating Submicron Aerosol Mixing State at the Global Scale With Machine Learning and Earth System Modeling

Zheng

Curtis

Yao

et al. 2021

Earth and Space Science

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This study integrates machine learning and particle‐resolved aerosol simulations to develop emulators that predict submicron aerosol mixing state indices from the Earth system model (ESM) simulations. The emulators predict aerosol mixing state using only quantities that are predicted by the ESM, including bulk aerosol species concentrations, which do not by themselves carry mixing state information. We used PartMC‐MOSAIC as the particle‐resolved model and NCAR's CESM as the ESM. We trained emulators for three different mixing state indices for submicron aerosol in terms of chemical species abundance (χa), the mixing of optically absorbing and nonabsorbing species (χo), and the mixing of hygroscopic and nonhygroscopic species (χh). Our global mixing state maps show considerable spatial and seasonal variability unique to each mixing state index. Seasonal averages varied spatially between 13% and 94% for χa, between 38% and 94% for χo, and between 20% and 87% for χh with global annual averages of 67%, 68%, and 56%, respectively. High values in one index can be consistent with low values in another index depending on the grouping of species and their relative abundance, meaning that each mixing state index captures different aspects of the population mixing state. Although a direct validation with observational data has not been possible yet, our results are consistent with mixing state index values derived from ambient observations. This work is a prototypical example of using machine learning emulators to add information to ESM simulations.

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Comprehensive isoprene and terpene gas-phase chemistry improves simulated surface ozone in the southeastern US

Cited by 69 publications

References 188 publications

The Chemistry Mechanism in the Community Earth System Model Version 2 (CESM2)

The Chemistry Mechanism in the Community Earth System Model Version 2 (CESM2)

Future changes in isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) under the shared socioeconomic pathways: the importance of explicit chemistry

Estimating Submicron Aerosol Mixing State at the Global Scale With Machine Learning and Earth System Modeling

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