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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Convective Transport of Very-short-lived Bromocarbons to the Stratosphere

We use the NASA GEOS Chemistry Climate Model (GEOSCCM) to quantify the contribution of two most important brominated very short-lived substances (VSLS), bromoform (CHBr3) and dibromomethane (CH2Br2), to stratospheric bromine and its sensitivity to convection strength. Model simulations suggest that the most active transport of VSLS from the marine boundary layer through the tropopause occurs over the tropical Indian Ocean, the Western Pacific warm pool, and off the Pacific coast of Mexico. Together, convective lofting of CHBr3 and CH2Br2 and their degradation products supplies ∼8 ppt total bromine to the base of the Tropical Tropopause Layer (TTL, ∼150 hPa), similar to the amount of VSLS organic bromine available in the marine boundary layer (∼7.8-8.4 ppt) in the above active convective lofting regions. Of the total ∼8 ppt VSLS-originated bromine that enters the base of TTL at ∼150 hPa, half is in the form of source gas injection (SGI) and half as product gas injection (PGI). Only a small portion (< 10%) the VSLS-originated bromine is removed via wet scavenging in the TTL before reaching the lower stratosphere. On global and annual average, CHBr3 and CH2Br2, together, contribute ∼7.7 pptv to the present-day inorganic bromine in the stratosphere. However, varying model deep convection strength between maximum and minimum convection conditions can introduce a ∼2.6 pptv uncertainty in the contribution of VSLS to inorganic bromine in the stratosphere (BryVSLS). Contrary to the conventional wisdom, minimum convection condition leads to a larger BryVSLS as the reduced scavenging in soluble product gases, thus a significant increase in PGI (2-3 ppt), greatly exceeds the relative minor decrease in SGI (a few 10ths ppt.

bromine↗
NASA NTRS2020

Evaluation of the Stratospheric and Tropospheric Bromine Burden over Fairbanks, Alaska Based on Column Retrievals of Bromine Monoxide

In spring 2011, columns of bromine monoxide (BrO) were retrieved over Fairbanks, Alaska using a ground-based multifunction differential optical absorption spectroscopy (MFDOAS) instrument. MFDOAS vertical column BrO is consistently lower than retrievals from the satellite-based Ozone Monitoring Instrument (OMI), with a relative bias of 20 ± 14%. Numerous tropical-based studies suggest that 5 ± 2 ppt of bromine from very short-lived substances (VSLS) reaches the stratosphere. We evaluate upper limits on the contribution of VSLS to stratospheric bromine by treating the column retrievals of BrO as purely stratospheric and modeling the ratio of BrO to total inorganic bromine. The OMI and MFDOAS retrievals respectively present 8 and 5 ppt upper limits on the stratospheric injection of VSLS, and kinetic uncertainties in the daytime partitioning of bromine species decrease both values by ~1.6 ppt. The OMI-based estimate is in agreement with the 5 ppt tropical-based value for stratospheric injection of VSLS if the tropospheric column of BrO is 1.5 × 10(exp 13) molecules/cu. cm over Fairbanks, which is within the range of uncertainty of a second ground-based instrument that monitored tropospheric BrO during the campaign. Because our ground-based instruments detected no BrO near the surface, this value for tropospheric BrO would originate from the free troposphere and is in agreement with previous retrievals of background tropospheric BrO. Our calculations of tropospheric BrO over Fairbanks are most sensitive to uncertainties in the stratospheric loading of VSLS, followed by the difference between the OMI and MFDOAS retrievals of BrO.

Pamela A. Wales↗
NASA NTRS2013

Evaluating Global Emission Inventories of Biogenic Bromocarbons

Emissions of halogenated very short-lived substances (VSLS) are poorly constrained. However, their inclusion in global models is required to simulate a realistic inorganic bromine (Bry) loading in both the troposphere, where bromine chemistry perturbs global oxidizing capacity, and in the stratosphere, where it is a major sink for ozone (O3). We have performed simulations using a 3-D chemical transport model (CTM) including three top-down and a single bottom-up derived emission inventory of the major brominated VSLS bromoform (CHBr3) and dibromomethane (CH2Br2). We perform the first concerted evaluation of these inventories, comparing both the magnitude and spatial distribution of emissions. For a quantitative evaluation of each inventory, model output is compared with independent long-term observations at National Oceanic and Atmospheric Administration (NOAA) ground-based stations and with aircraft observations made during the NSF (National Science Foundation) HIAPER Pole-to-Pole Observations (HIPPO) project. For CHBr3, the mean absolute deviation between model and surface observation ranges from 0.22 (38 %) to 0.78 (115 %) parts per trillion (ppt) in the tropics, depending on emission inventory. For CH2Br2, the range is 0.17 (24 %) to 1.25 (167 %) ppt. We also use aircraft observations made during the 2011 Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere (SHIVA) campaign, in the tropical western Pacific. Here, the performance of the various inventories also varies significantly, but overall the CTM is able to reproduce observed CHBr3 well in the free troposphere using an inventory based on observed sea-to-air fluxes. Finally, we identify the range of uncertainty associated with these VSLS emission inventories on stratospheric bromine loading due to VSLS (Br(VSLS/y)). Our simulations show Br(VSLS/y) ranges from approximately 4.0 to 8.0 ppt depending on the inventory. We report an optimized estimate at the lower end of this range (approximately 4 ppt) based on combining the CHBr3 and CH2Br2 inventories which give best agreement with the compilation of observations in the tropics.

bromocarbons↗
DOE OSTI2026

Voltage Service Limits Smart Contract Using Distributed Ledger Technology for Electrical Utility Grid with Customer-Owned Generator

Modern electrical grids face growing stability risks from customer-owned generators, especially at points of common couplings (PCCs). Disruptive behavior from power-electronic sources can cause protective relays to isolate problematic generators, making measurement integrity critical. This article presents a distributed ledger technology (DLT) approach that uses smart contracts to evaluate PCC voltage measurements and trigger backup breaker operations. The approach is framed as a verifiable, multi-organization attestation and audit layer, not as a real-time control security mechanism. In the proposed architecture, voltage measurements from a hardware protective relay are anchored on a DLT through the Cyber Grid Guard (CGG) system for attestation by both the grid utility and customer-owned generator. A Voltage Service Limits (VSLs) smart contract evaluates the on-chain measurements against allowable phase-voltage limits derived from the ANSI C84.1 standard. The framework is validated in a hardware-relay-in-the-loop test bed under sustained-undervoltage, sustained-overvoltage, and transient line-to-line fault scenarios. The results show that the VSL smart contract can process these measurements and issue backup breaker actions consistent with the defined service-limit criteria, demonstrating the DLT potential as a verifiable audit layer at the PCC that complements primary protection.

cyber security↗
NASA NTRS2010

Finding the Missing Stratospheric Br(sub y): A Global Modeling Study of CHBr3 and CH2Br2

Recent in situ and satellite measurements suggest a contribution of ~5 pptv to stratospheric inorganic bromine from short-lived bromocarbons. We conduct a modeling study of the two most important short-lived bromocarbons, bromoform (CHBr3) and dibromomethane (CH2Br2), with the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to account for this missing stratospheric bromine. We derive a "top-down" emission estimate of CHBr3 and CH2Br2 using airborne measurements in the Pacific and North American troposphere and lower stratosphere obtained during previous NASA aircraft campaigns. Our emission estimate suggests that to reproduce the observed concentrations in the free troposphere, a global oceanic emission of 425 Gg Br yr(exp -1) for CHBr3 and 57 Gg Br yr(exp -l) for CH2Br2 is needed, with 60% of emissions from open ocean and 40% from coastal regions. Although our simple emission scheme assumes no seasonal variations, the model reproduces the observed seasonal variations of the short-lived bromocarbons with high concentrations in winter and low concentrations in summer. This indicates that the seasonality of short-lived bromocarbons is largely due to seasonality in their chemical loss and transport. The inclusion of CHBr3 and CH2Br2 contributes ~5 pptv bromine throughout the stratosphere. Both the source gases and inorganic bromine produced from source gas degradation (Br~SLS) in the troposphere are transported into the stratosphere, and are equally important. Inorganic bromine accounts for half (2.5 pptv) of the bromine from the inclusion of CHBr3 and CHzBr2 near the tropical tropopause and its contribution rapidly increases to ~ 100% as altitude increases. More than 85% of the wet scavenging of Br(sub y)(sup VSLS) occurs in large-scale precipitation below 500 hPa. Our sensitivity study with wet scavenging in convective updrafts switched off suggests that Br(sub y)(sup SLS) in the stratosphere is not sensitive to convection. Convective scavenging only accounts for ~0.2 pptv (4%) difference in inorganic bromine delivered to the stratosphere.

Liang, Q.↗
NASA NTRS2017

Concerns for Ozone Recovery

Reactive halogen gases containing chlorine (Cl) or bromine (Br) can destroy stratospheric ozone via catalytic cycles. The main sources of atmospheric reactive halogen are the long-lived synthetic chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), carbon tetrachloride (CCl4), methyl chloroform (CH3CCl3), and bromine-containing halons, all of which persist in the atmosphere for years. These ozone-depleting substances are now controlled under the Montreal Protocol and its amendments. Natural methyl bromide (CH3Br) and methyl chloride (CH3Cl) emissions are also important long-lived sources of atmospheric reactive halogen. Rising concentrations of very-short-lived substances (VSLSs) with atmospheric lifetimes of less than half a year may also contribute to future stratospheric ozone depletion. A greater concern for ozone layer recovery is incomplete compliance with the Montreal Protocol, which will impact stratospheric ozone for many decades, as well as rising natural emissions as a result of climate change.

VSLS↗