163 research outputs found
Flavor hierarchies, flavor anomalies, and Higgs mass from a warped extra dimension
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement 833280 (FLAY), and by the Swiss National Science Foundation (SNF) under con-tract 200020_204428. The work of JF has been supported by the Spanish Ministry of Science and Innovation (MCIN) and the Euro-pean Union NextGenerationEU/PRTR under grant IJC2020-043549-I, by the MCIN grant PID2019-106087GB-C22, and by the Junta de Andalucía grants P18-FR-4314 (FEDER) and FQM101.The recent B-meson anomalies are coherently explained at the TeV scale by 4321 gauge models with hierarchical couplings reminiscent of the Standard Model Yukawas. We show that such models arise as the low-energy limit of a complete theory of flavor, based on a warped fifth dimension where each Standard Model family is quasi-localized on a different brane. The Higgs is identified as a pseudo-Nambu-Goldstone boson emerging from the same dynamics responsible for 4321 symmetry breaking. This novel construction unifies quarks and leptons in a flavor non-universal manner, provides a natural description of flavor hierarchies, and addresses the electroweak hierarchy problem.European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement 833280 (FLAY)Swiss National Science Foundation (SNF) under con-tract 200020_204428Spanish Ministry of Science and Innovation (MCIN) and the European Union NextGeneration EU/PRTR under grant IJC2020-043549-IMCIN grant PID2019-106087GB-C22Junta de Andalucía grants P18-FR-4314 (FEDER) and FQM10
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Highly Speciated Measurements of Terpenoids Emitted from Laboratory and Mixed-Conifer Forest Prescribed Fires
Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol
To better understand the effects of wildfires on air quality and climate, it is important to assess the occurrence of chromophoric compounds in smoke and characterize their optical properties. This study explores the molecular composition of light-absorbing organic aerosol, or brown carbon (BrC), sampled at the Missoula Fire Sciences laboratory as a part of the FIREX Fall 2016 lab intensive. A total of 12 biomass fuels from different plant types were tested, including gymnosperm (coniferous) and angiosperm (flowering) plants and different ecosystem components such as duff, litter, and canopy. Emitted biomass burning organic aerosol (BBOA) particles were collected onto Teflon filters and analyzed offline using high-performance liquid chromatography coupled to a photodiode array spectrophotometer and a high-resolution mass spectrometer (HPLC-PDA-HRMS). Separated BrC chromophores were classified by their retention times, absorption spectra, integrated absorbance in the near-UV and visible spectral range (300-700 nm), and chemical formulas from the accurate m/z measurements. BrC chromophores were grouped into the following classes and subclasses: lignin-derived products, which include lignin pyrolysis products; distillation products, which include coumarins and flavonoids; nitroaromatics; and polycyclic aromatic hydrocarbons (PAHs). The observed classes and subclasses were common across most fuel types, although specific BrC chromophores varied based on plant type (gymnosperm or angiosperm) and ecosystem component(s) burned. To study the stability of the observed BrC compounds with respect to photodegradation, BBOA particle samples were irradiated directly on filters with near UV (300-400 nm) radiation, followed by extraction and HPLC-PDA-HRMS analysis. Lifetimes of individual BrC chromophores depended on the fuel type and the corresponding combustion condition. Lignin-derived and flavonoid classes of BrC generally had the longest lifetimes with respect to UV photodegradation. Moreover, lifetimes for the same type of BrC chromophores varied depending on biomass fuel and combustion conditions. While individual BrC chromophores disappeared on a timescale of several days, the overall light absorption by the sample persisted longer, presumably because the condensed-phase photochemical processes converted one set of chromophores into another without complete photobleaching or from undetected BrC chromophores that photobleached more slowly. To model the effect of BrC on climate, it is important to understand the change in the overall absorption coefficient with time. We measured the equivalent atmospheric lifetimes of the overall BrC absorption coefficient, which ranged from 10 to 41 d, with subalpine fir having the shortest lifetime and conifer canopies, i.e., juniper, having the longest lifetime. BrC emitted from biomass fuel loads encompassing multiple ecosystem components (litter, shrub, canopy) had absorption lifetimes on the lower end of the range. These results indicate that photobleaching of BBOA by condensed-phase photochemistry is relatively slow. Competing chemical aging mechanisms, such as heterogeneous oxidation by OH, may be more important for controlling the rate of BrC photobleaching in BBOA
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Primary emissions of glyoxal and methylglyoxal from laboratory measurements of open biomass burning
We report the emissions of glyoxal and methylglyoxal from the open burning of biomass during the NOAA-led 2016 FIREX intensive at the Fire Sciences Laboratory in Missoula, MT. Both compounds were measured using cavity-enhanced spectroscopy, which is both more sensitive and more selective than methods previously used to determine emissions of these two compounds. A total of 75 burns were conducted, using 33 different fuels in 8 different categories, providing a far more comprehensive dataset for emissions than was previously available. Measurements of methylglyoxal using our instrument suffer from spectral interferences from several other species, and the values reported here are likely underestimates, possibly by as much as 70 %. Methylglyoxal emissions were 2-3 times higher than glyoxal emissions on a molar basis, in contrast to previous studies that report methylglyoxal emissions lower than glyoxal emissions. Methylglyoxal emission ratios for all fuels averaged 3.6±2.4 ppbv methylglyoxal (ppmv CO) 1, while emission factors averaged 0.66±0.50 g methylglyoxal (kg fuel burned) 1. Primary emissions of glyoxal from biomass burning were much lower than previous laboratory measurements but consistent with recent measurements from aircraft. Glyoxal emission ratios for all fuels averaged 1.4±0.7 ppbv glyoxal (ppmv CO) 1, while emission factors averaged 0.20±0.12 g glyoxal (kg fuel burned) 1, values that are at least a factor of 4 lower than assumed in previous estimates of the global glyoxal budget. While there was significant variability in the glyoxal emission ratios and factors between the different fuel groups, glyoxal and formaldehyde were highly correlated during the course of any given fire, and the ratio of glyoxal to formaldehyde, RGF, was consistent across many different fuel types, with an average value of 0.068±0.018. While RGF values for fresh emissions were consistent across many fuel types, further work is required to determine how this value changes as the emissions age
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Airborne measurements of western U.S. wildfire emissions: Comparison with prescribed burning and air quality implications
Wildfires emit significant amounts of pollutants that degrade air quality. Plumes from three wildfires in the western U.S. were measured from aircraft during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and the Biomass Burning Observation Project (BBOP), both in summer 2013. This study reports an extensive set of emission factors (EFs) for over 80 gases and 5 components of submicron particulate matter (PM1) from these temperate wildfires. These include rarely, or never before, measured oxygenated volatile organic compounds and multifunctional organic nitrates. The observed EFs are compared with previous measurements of temperate wildfires, boreal forest fires, and temperate prescribed fires. The wildfires emitted high amounts of PM1 (with organic aerosol (OA) dominating the mass) with an average EF that is more than 2 times the EFs for prescribed fires. The measured EFs were used to estimate the annual wildfire emissions of carbon monoxide, nitrogen oxides, total nonmethane organic compounds, and PM1 from 11 western U.S. states. The estimated gas emissions are generally comparable with the 2011 National Emissions Inventory (NEI). However, our PM1 emission estimate (1530 ± 570 Gg yr-1) is over 3 times that of the NEI PM2.5 estimate and is also higher thanthe PM2.5 emitted from all other sources in these states in the NEI. This study indicates that the source of OA from biomass burning in the western states is significantly underestimated. In addition, our results indicate that prescribed burning may be an effective method to reduce fine particle emissions
Characterization of a catalyst-based conversion technique to measure total particulate nitrogen and organic carbon and comparison to a particle mass measurement instrument
The chemical composition of aerosol particles is a key aspect in determining their impact on the environment. For example, nitrogen-containing particles impact atmospheric chemistry, air quality, and ecological N deposition. Instruments that measure total reactive nitrogen (Nr Combining double low line all nitrogen compounds except for N2 and N2O) focus on gas-phase nitrogen and very few studies directly discuss the instrument capacity to measure the mass of Nr-containing particles. Here, we investigate the mass quantification of particle-bound nitrogen using a custom Nr system that involves total conversion to nitric oxide (NO) across platinum and molybdenum catalysts followed by NOĝ\u27O3 chemiluminescence detection. We evaluate the particle conversion of the Nr instrument by comparing to mass-derived concentrations of size-selected and counted ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), ammonium chloride (NH4Cl), sodium nitrate (NaNO3), and ammonium oxalate ((NH4)2C2O4) particles determined using instruments that measure particle number and size. These measurements demonstrate Nr-particle conversion across the Nr catalysts that is independent of particle size with 98ĝ€±ĝ€10ĝ€% efficiency for 100-600ĝ€nm particle diameters. We also show efficient conversion of particle-phase organic carbon species to CO2 across the instrument\u27s platinum catalyst followed by a nondispersive infrared (NDIR) CO2 detector. However, the application of this method to the atmosphere presents a challenge due to the small signal above background at high ambient levels of common gas-phase carbon compounds (e.g., CO2). We show the Nr system is an accurate particle mass measurement method and demonstrate its ability to calibrate particle mass measurement instrumentation using single-component, laboratory-generated, Nr-containing particles below 2.5ĝ€μm in size. In addition we show agreement with mass measurements of an independently calibrated online particle-into-liquid sampler directly coupled to the electrospray ionization source of a quadrupole mass spectrometer (PILS-ESI/MS) sampling in the negative-ion mode. We obtain excellent correlations (R2ĝ€Combining double low line 0.99) of particle mass measured as Nr with PILS-ESI/MS measurements converted to the corresponding particle anion mass (e.g., nitrate, sulfate, and chloride). The Nr and PILS-ESI/MS are shown to agree to within ĝ1/4ĝ€6ĝ€% for particle mass loadings of up to 120ĝ€μgĝ€mĝ\u273. Consideration of all the sources of error in the PILS-ESI/MS technique yields an overall uncertainty of ±20ĝ€% for these single-component particle streams. These results demonstrate the Nr system is a reliable direct particle mass measurement technique that differs from other particle instrument calibration techniques that rely on knowledge of particle size, shape, density, and refractive index
Constraining emissions of volatile organic compounds from western US wildfires with WE-CAN and FIREX-AQ airborne observations
The impact of biomass burning (BB) on the atmospheric burden of volatile organic compounds (VOCs) is highly uncertain. Here we apply the GEOS-Chem
chemical transport model (CTM) to constrain BB emissions in the western USA at ∼ 25 km resolution. Across three BB emission inventories
widely used in CTMs, the inventory–inventory comparison suggests that the totals of 14 modeled BB VOC emissions in the western USA agree with each
other within 30 %–40 %. However, emissions for individual VOCs can differ by a factor of 1–5, driven by the regionally averaged emission
ratios (ERs, reflecting both assigned ERs for specific biome and vegetation classifications) across the three inventories. We further evaluate GEOS-Chem
simulations with aircraft observations made during WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen) and
FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality) field campaigns. Despite being driven by different global BB
inventories or applying various injection height assumptions, the model–observation comparison suggests that GEOS-Chem simulations underpredict
observed vertical profiles by a factor of 3–7. The model shows small to no bias for most species in low-/no-smoke conditions. We thus attribute the
negative model biases mostly to underestimated BB emissions in these inventories. Tripling BB emissions in the model reproduces observed vertical
profiles for primary compounds, i.e., CO, propane, benzene, and toluene. However, it shows no to less significant improvements for oxygenated
VOCs, particularly for formaldehyde, formic acid, acetic acid, and lumped ≥ C3 aldehydes, suggesting the model is missing secondary
sources of these compounds in BB-impacted environments. The underestimation of primary BB emissions in inventories is likely attributable to
underpredicted amounts of effective dry matter burned, rather than errors in fire detection, injection height, or ERs, as constrained by aircraft
and ground measurements. We cannot rule out potential sub-grid uncertainties (i.e., not being able to fully resolve fire plumes) in the nested
GEOS-Chem which could explain the negative model bias partially, though back-of-the-envelope calculation and evaluation using longer-term ground
measurements help support the argument of the dry matter burned underestimation. The total ERs of the 14 BB VOCs implemented in GEOS-Chem only
account for half of the total 161 measured VOCs (∼ 75 versus 150 ppb ppm−1). This reveals a significant amount of missing reactive
organic carbon in widely used BB emission inventories. Considering both uncertainties in effective dry matter burned (× 3) and unmodeled
VOCs (× 2), we infer that BB contributed to 10 % in 2019 and 45 % in 2018 (240 and 2040 Gg C) of the total VOC primary
emission flux in the western USA during these two fire seasons, compared to only 1 %–10 % in the standard GEOS-Chem.</p
Constraining emissions of volatile organic compounds from western US wildfires with WE-CAN and FIREX-AQ airborne observations
The impact of biomass burning (BB) on the atmospheric burden of volatile organic compounds (VOCs) is highly uncertain. Here we apply the GEOS-Chem chemical transport model (CTM) to constrain BB emissions in the western US at ~25 km resolution. Across three BB emission inventories widely used in CTMs, the total of 14 modeled BB VOC emissions in the western US agree with each other within 30–40 %. However, emissions for individual VOC differ by up to a factor of 5 (i.e., lumped ≥ C4 alkanes), driven by the regionally averaged emission ratios (ERs) among inventories. We further evaluate GEOS-Chem simulations with aircraft observations made during WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen) and FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality) field campaigns. Despite being driven by different global BB inventories or applying various injection height assumptions, GEOS-Chem simulations underpredict observed vertical profiles by a factor of 3–7. The model shows small-to-no bias for most species in low/no smoke conditions. We thus attribute the negative model biases mostly to underestimated BB emissions in these inventories. Tripling BB emissions in the model reproduces observed vertical profiles for primary compounds, i.e., CO, propane, benzene, and toluene. However, it shows no-to-less significant improvements for oxygenated VOCs, particularly formaldehyde, formic acid, acetic acid, and lumped ≥ C3 aldehydes, suggesting the model is missing secondary sources of these compounds in BB-impacted environments. The underestimation of primary BB emissions in inventories is likely attributable to underpredicted amounts of effective dry matter burned, rather than errors in fire detection, injection height, or ERs. We cannot rule out potential sub-grid uncertainties (i.e., not being able to fully resolve fire plumes) in the nested GEOS-Chem which could explain the model negative bias partially, though the back-of-the-envelope calculation and evaluation using longer-term ground measurements help increase the argument of the dry matter burned underestimation. The ERs of the 14 BB VOCs implemented in GEOS-Chem account for about half of the total 161 measured VOCs (~75 versus 150 ppb ppm-1). This reveals a significant amount of missing reactive organic carbon in widely-used BB emission inventories. Considering both uncertainties in effective dry matter burned and unmodeled VOCs, we infer that BB contributed up to 10 % in 2019 and 45 % in 2018 (240 and 2040 GgC) of the total VOC primary emission flux in the western US during these two fire seasons, compared to only 1–10 % in the standard GEOS-Chem.</p
Speciated and total emission factors of particulate organics from burning western US wildland fuels and their dependence on combustion efficiency
Western US wildlands experience frequent and large-scale wildfires which are
predicted to increase in the future. As a result, wildfire smoke emissions
are expected to play an increasing role in atmospheric chemistry while
negatively impacting regional air quality and human health. Understanding the
impacts of smoke on the environment is informed by identifying and
quantifying the chemical compounds that are emitted during wildfires and by
providing empirical relationships that describe how the amount and
composition of the emissions change based upon different fire conditions and
fuels. This study examined particulate organic compounds emitted from burning
common western US wildland fuels at the US Forest Service Fire Science
Laboratory. Thousands of intermediate and semi-volatile organic compounds
(I/SVOCs) were separated and quantified into fire-integrated emission factors
(EFs) using a thermal desorption, two-dimensional gas chromatograph with
online derivatization coupled to an electron ionization/vacuum ultraviolet
high-resolution time-of-flight mass spectrometer
(TD-GC × GC-EI/VUV-HRToFMS). Mass spectra, EFs as a function of
modified combustion efficiency (MCE), fuel source, and other defining
characteristics for the separated compounds are provided in the accompanying
mass spectral library. Results show that EFs for total organic carbon (OC),
chemical families of I/SVOCs, and most individual I/SVOCs span 2–5 orders of
magnitude, with higher EFs at smoldering conditions (low MCE) than flaming.
Logarithmic fits applied to the observations showed that log (EFs) for
particulate organic compounds were inversely proportional to MCE. These
measurements and relationships provide useful estimates of EFs for OC,
elemental carbon (EC), organic chemical families, and individual I/SVOCs as a
function of fire conditions.</p
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