| Autor: |
Vermeuel, Michael P., Millet, Dylan B., Farmer, Delphine K., Pothier, Matson A., Link, Michael F., Riches, Mj, Williams, Sara, Garofalo, Lauren A. |
| Předmět: |
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| Zdroj: |
Journal of Geophysical Research. Atmospheres; 7/27/2023, Vol. 128 Issue 14, p1-20, 20p |
| Abstrakt: |
We use observations from dual high‐resolution mass spectrometers to characterize ecosystem‐atmosphere fluxes of reactive carbon across an extensive range of volatile organic compounds (VOCs) and test how well that exchange is represented in current chemical transport models. Measurements combined proton‐transfer reaction mass spectrometry (PTRMS) and iodide chemical ionization mass spectrometry (ICIMS) over a Colorado pine forest; together, these techniques have been shown to capture the majority of ambient VOC abundance and reactivity. Total VOC mass and associated OH reactivity fluxes were dominated by emissions of 2‐methyl‐3‐buten‐2‐ol, monoterpenes, and small oxygenated VOCs, with a small number of compounds detected by PTRMS driving the majority of both net and upward exchanges. Most of these dominant species are explicitly included in chemical models, and we find here that GEOS‐Chem accurately simulates the net and upward VOC mass and OH reactivity fluxes under clear sky conditions. However, large upward terpene fluxes occurred during sustained rainfall, and these are not captured by the model. Far more species contributed to the downward fluxes than are explicitly modeled, leading to a major underestimation of this key sink of atmospheric reactive carbon. This model bias mainly reflects missing and underestimated concentrations of depositing species, though inaccurate deposition velocities also contribute. The deposition underestimate is particularly large for assumed isoprene oxidation products, organic acids, and nitrates—species that are primarily detected by ICIMS. Net ecosystem‐atmosphere fluxes of ozone reactivity were dominated by sesquiterpenes and monoterpenes, highlighting the importance of these species for predicting near‐surface ozone, oxidants, and aerosols. Plain Language Summary: Reactive carbon species in the atmosphere have a strong influence on air quality and climate and require accurate modeling to understand their global impacts. Natural ecosystems such as forests both emit and take up reactive carbon to and from the atmosphere, acting simultaneously as the largest source and an important sink of these species. We performed the most comprehensive measurements to date of this two‐way reactive carbon exchange over a pine forest. We observed that the upward reactive carbon exchange was controlled by just a few known species and was much larger than the downward exchange, which was composed of far more species. We compared the observations to chemical model predictions and found that the model generally captures the net reactive carbon exchange over this forest because the few species dominating that exchange are included in the model. However, the model does not adequately simulate the many depositing species, leading to a large underestimate for this sink of atmospheric reactive carbon. Key Points: A small number of known organic compounds dominate the net and upward reactive carbon fluxes over a coniferous forestPTRMS captures VOCs controlling the net and upward fluxes, while ICIMS measures a range of important depositing speciesFar more VOCs contribute to the downward fluxes than are currently modeled, leading to a major sink underestimate [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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