6 research outputs found

    Connecting Land–Atmosphere Interactions to Surface Heterogeneity in CHEESEHEAD19

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    The Chequamegon Heterogeneous Ecosystem Energy-Balance Study Enabled by a High-Density Extensive Array of Detectors 2019 (CHEESEHEAD19) is an ongoing National Science Foundation project based on an intensive field campaign that occurred from June to October 2019. The purpose of the study is to examine how the atmospheric boundary layer (ABL) responds to spatial heterogeneity in surface energy fluxes. One of the main objectives is to test whether lack of energy balance closure measured by eddy covariance (EC) towers is related to mesoscale atmospheric processes. Finally, the project evaluates data-driven methods for scaling surface energy fluxes, with the aim to improve model–data comparison and integration. To address these questions, an extensive suite of ground, tower, profiling, and airborne instrumentation was deployed over a 10 km × 10 km domain of a heterogeneous forest ecosystem in the Chequamegon–Nicolet National Forest in northern Wisconsin, United States, centered on an existing 447-m tower that anchors an AmeriFlux/NOAA supersite (US-PFa/WLEF). The project deployed one of the world’s highest-density networks of above-canopy EC measurements of surface energy fluxes. This tower EC network was coupled with spatial measurements of EC fluxes from aircraft; maps of leaf and canopy properties derived from airborne spectroscopy, ground-based measurements of plant productivity, phenology, and physiology; and atmospheric profiles of wind, water vapor, and temperature using radar, sodar, lidar, microwave radiometers, infrared interferometers, and radiosondes. These observations are being used with large-eddy simulation and scaling experiments to better understand submesoscale processes and improve formulations of subgrid-scale processes in numerical weather and climate models

    In-Canopy Chemistry, Emissions, Deposition, and Surface Reactivity Compete to Drive Bidirectional Forest-Atmosphere Exchange of VOC Oxidation Products

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    Dry deposition is an important sink of oxygenated volatile organic compounds (OVOCs) in forest ecosystems. In the summer of 2021, we measured concentration gradients and exchange velocities of oxidation products of isoprene and 3-methyl-3-buten-2-ol (MBO) from a Colorado Ponderosa pine forest as part of the Flux Closure Study (FluCS). MBO oxidation products exhibited bidirectional exchange over the forest. Vertical gradients of MBO oxidation products reveal in-canopy chemical production as a daytime source, whereas air transported from the urban outflow of the front range creates periods of enhanced deposition. Differences between our observed deposition velocities over the arid, sparse pine forest and those from a previous study over a temperate, dense mixed forest suggest that ecosystem type may impact deposition rates in ways not currently captured by GEOS-Chem. We show that a previously inferred increased OVOC solubility threshold on leaf cuticles is not likely to explain the observed rapid rates of deposition but instead suggest that peroxides/epoxides could undergo reactive uptake to broadleaf vegetation while organic nitrates could undergo reactive uptake to pine needles. We point to the need to understand the role of reactive OVOC uptake and its potential implications for bidirectional ecosystem-atmosphere exchange

    Rapid cloud removal of dimethyl sulfide oxidation products limits SO2 and cloud condensation nuclei production in the marine atmosphere.

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    Oceans emit large quantities of dimethyl sulfide (DMS) to the marine atmosphere. The oxidation of DMS leads to the formation and growth of cloud condensation nuclei (CCN) with consequent effects on Earth's radiation balance and climate. The quantitative assessment of the impact of DMS emissions on CCN concentrations necessitates a detailed description of the oxidation of DMS in the presence of existing aerosol particles and clouds. In the unpolluted marine atmosphere, DMS is efficiently oxidized to hydroperoxymethyl thioformate (HPMTF), a stable intermediate in the chemical trajectory toward sulfur dioxide (SO2) and ultimately sulfate aerosol. Using direct airborne flux measurements, we demonstrate that the irreversible loss of HPMTF to clouds in the marine boundary layer determines the HPMTF lifetime (Ď„HPMTF < 2 h) and terminates DMS oxidation to SO2 When accounting for HPMTF cloud loss in a global chemical transport model, we show that SO2 production from DMS is reduced by 35% globally and near-surface (0 to 3 km) SO2 concentrations over the ocean are lowered by 24%. This large, previously unconsidered loss process for volatile sulfur accelerates the timescale for the conversion of DMS to sulfate while limiting new particle formation in the marine atmosphere and changing the dynamics of aerosol growth. This loss process potentially reduces the spatial scale over which DMS emissions contribute to aerosol production and growth and weakens the link between DMS emission and marine CCN production with subsequent implications for cloud formation, radiative forcing, and climate
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