Stratospheric photochemistry:
Explore the source record for details and available documents.
stratospheric gases halogen↗
SEARCH · Search NASA
Results for “Photochemistry”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Impact of Lightning-NO Emissions on Summertime U.S. Photochemistry as Determined Using the CMAQ Model with NLDN-Constrained Flash Rates
Lightning-NO emissions are responsible for 15-30 ppbv enhancements in upper tropospheric ozone over the eastern United States during the summer time. Enhancements vary from year to year but were particularly large during the summer of 2006, a period during which meteorological conditions were particularly conducive to ozone formation. A lightning-NO parameterization has been developed that can be used with the CMAQ model. Lightning-NO emissions in this scheme are assumed to be proportional to convective precipitation rate and scaled so that monthly average flash rates in each grid box match National Lightning Detection Network (NLDN) observed flash rates after adjusting for climatological intracloud to cloud-to-ground (IC/CG) ratios. The contribution of lightning-NO emissions to eastern United States NOx and ozone distributions during the summer of 2006 will be evaluated by comparing results of 12- km CMAQ simulations with and without lightning-NO emissions to measurements from the IONS field campaign and to satellite retrievals from the Tropospheric Emission Spectrometer (TES) and the Ozone Monitoring Instrument (OMI) aboard the Aura satellite. Special attention will be paid to the impact of the assumed vertical distribution of emissions on upper tropospheric NOx and ozone amounts.
Allen, Dale↗
Photochemistry of Pyrimidine in Astrophysical Ices: Formation of Nucleobases and Other Prebiotic Species
Nucleobases are N-heterocycles that are the informational subunits of DNA and RNA. They are divided into two molecular groups: pyrimidine bases (uracil, cytosine, and thymine) and purine bases (adenine and guanine). Nucleobases have been detected in meteorites, and their extraterrestrial origin confirmed by isotopic measurements. Although no N-heterocycles have ever been observed in the ISM, the positions of the 6.2- m interstellar emission features suggest a population of such molecules is likely to be present. However, laboratory experiments have shown that the ultraviolet (UV) irradiation of pyrimidine in ices of astrophysical relevance such as H2O, NH3, CH3OH, CH4, CO, or combinations of these at low temperature (less than or equal to 20 K) leads to the formation of several pyrimidine derivatives including the nucleobases uracil and cytosine, as well as precursors such as 4(3H)-pyrimidone and 4-aminopyrimidine. Quantum calculations on the formation of 4(3H)-pyrimidone and uracil from the irradiation of pyrimidine in pure H2O ices are in agreement with their experimental formation pathways.10 In those residues, other species of prebiotic interest such as urea as well as the amino acids glycine and alanine could also be identified. However, only very small amounts of pyrimidine derivatives containing CH3 groups could be detected, suggesting that the addition of methyl groups to pyrimidine is not an efficient process. For this reason, the nucleobase thymine was not observed in any of the samples. In this work, we study the formation of nucleobases and other photo-products of prebiotic interest from the UV irradiation of pyrimidine in ices containing H2O, NH3, CH3OH, and CO, mixed in astrophysical proportions.
Nuevo, Michel↗
Impacts of Brown Carbon from Biomass Burning on Surface UV and Ozone Photochemistry in the Amazon Basin
The spectral dependence of light absorption by atmospheric particulate matter has major implications for air quality and climate forcing, but remains uncertain especially in tropical areas with extensive biomass burning. In the September-October 2007 biomass-burning season in Santa Cruz, Bolivia, we studied light absorbing (chromophoric) organic or brown carbon (BrC) with surface and space-based remote sensing. We found that BrC has negligible absorption at visible wavelengths, but significant absorption and strong spectral dependence at UV wavelengths. Using the ground-based inversion of column effective imaginary refractive index in the range 305368nm, we quantified a strong spectral dependence of absorption by BrC in the UV and diminished ultraviolet B (UV-B) radiation reaching the surface. Reduced UV-B means less erythema, plant damage, and slower photolysis rates. We use a photochemical box model to show that relative to black carbon (BC) alone, the combined optical properties of BrC and BC slow the net rate of production of ozone by up to 18 and lead to reduced concentrations of radicals OH, HO2, and RO2 by up to 17, 15, and 14, respectively. The optical properties of BrC aerosol change in subtle ways the generally adverse effects of smoke from biomass burning.
UV absorption OMI↗
Cloud Impacts on Photochemistry: Building a Climatology of Photolysis Rates from the Atmospheric Tomography Mission
Measurements from actinic flux spectroradiometers on board the NASA DC-8 during the Atmospheric Tomography (ATom) mission provide an extensive set of statistics on how clouds alter photolysis rates (J values) throughout the remote Pacific and Atlantic Ocean basins. J values control tropospheric ozone and methane abundances, and thus clouds have been included for more than three decades in tropospheric chemistry modeling. ATom made four profiling circumnavigations of the troposphere capturing each of the seasons during 2016–2018. This work examines J values from the Pacific Ocean flights of the first deployment, but publishes the complete Atom-1 data set (29 July to 23 August 2016). We compare the observed J values (every 3 s along flight track) with those calculated by nine global chemistry– climate/transport models (globally gridded, hourly, for a mid-August day). To compare these disparate data sets, we build a commensurate statistical picture of the impact of clouds on J values using the ratio of J -cloudy (standard, sometimes cloudy conditions) to J -clear (artificially cleared of clouds). The range of modeled cloud effects is inconsistently large but they fall into two distinct classes: (1) models with large cloud effects showing mostly enhanced J values aloft and or diminished at the surface and (2) models with small effects having nearly clear-sky J values much of the time. The ATom-1 measurements generally favor large cloud effects but are not precise or robust enough to point out the best cloud-modeling approach. The models here have resolutions of 50–200 km and thus reduce the occurrence of clear sky when averaging over grid cells. In situ measurements also average scattered sunlight over a mixed cloud field, but only out to scales of tens of kilometers. A primary uncertainty remains in the role of clouds in chemistry, in particular, how models average over cloud fields, and how such averages can simulate measurements.
actinic flux spectroradiometers↗
Laboratory Kinetics and Photochemistry for Earth and Planetary Atmospheres
No abstract provided
Zuraski, Kristen L↗
Impacts of Fires on Photochemistry: Observations of Peroxyacetyl Nitrate (PAN) from CrIS and AIRS
No abstract provided
Fischer, Emily↗
Production of Singlet Oxygen ( 1 O 2 ) during the Photochemistry of Aqueous Pyruvic Acid: The Effects of pH and Photon Flux under Steady-State O 2 (aq) Concentration
Explore the source record for details and available documents.
Alexis J. Eugene↗
Lucifer's Planet: Photolytic Hazes in the Atmosphere of 51 Eri b
We use a 1D model to address photochemistry and possible haze formation in the irradiated atmosphere of 51 Eri b (2016arXiv160407388Z). The intended focus was to have been on carbon and organic hazes, but sulfur photochemistry turns out to be interesting and possibly more important. The case for organic photochemical hazes is intriguing but falls short of being compelling. If organic hazes form abundantly, they are likeliest to do so if vertical mixing in 51 Eri b is weaker than in Jupiter, and they would be found below the altitudes where methane and water are photolyzed. The more novel result is that photochemistry turns H2S into elemental sulfur, here treated as S8. In the cooler models, S8 is predicted to condense in optically significant clouds of solid sulfur particles, whilst in the warmer models S8 remains a vapor along with several other sulfur allotropes that are both visually striking and potentially observable. For 51 Eri b, the division between models with and without condensed sulfur is at an effective temperature of 700 K, which is within error its actual effective temperature; the local temperature where sulfur condenses is between 280 and 320 K. The sulfur photochemistry we discuss is quite general and ought to be found in a wide variety of worlds over a broad temperature range, both colder and hotter than the 650-750 K range studied here, and we show that products of sulfur photochemistry will be nearly as abundant on planets where the UV irradiation is orders of magnitude weaker than it is on 51 Eri b.
photochemistry↗
Photolytic Hazes in the Atmosphere of 51 Eri b
We use a 1D model to address photochemistry and possible haze formation in the irradiated warm Jupiter 51 Eridani b. The intended focus was to be carbon, but sulfur photochemistry turns out to be important. The case for organic photochemical hazes is intriguing but falls short of being compelling. If they form, they are likeliest to do so if vertical mixing in 51 Eri b is weaker than in Jupiter, and they would be found below the regions where methane and water are photolyzed. The more novel result is that photochemistry turns H2S into elemental sulfur, here treated as S8. In the cooler models, S8 is predicted to condense in optically thick clouds of solid sulfur particles, whilst in the warmer models S8 remains a vapor along with several other sulfur allotropes that are both visually striking and potentially observable. For 51 Eri b, the division between models with and without condensed sulfur is at an effective temperature of 700 K, which is within error its actual effective temperature; the local temperature where sulfur condenses is between 280 and 320 K. The sulfur photochemistry we have discussed is quite general and ought to be found in a wide variety of worlds over a broad temperature range, both colder and hotter than the 650-750 K range studied here, and we show that products of sulfur photochemistry will be nearly as abundant on planets where the UV irradiation is orders of magnitude weaker than it is on 51 Eri b.
stars: individual(51 Eri b)↗
Ozone in the free atmosphere
The present book provides a summary of the state of scientific knowledge of stratospheric and free tropospheric ozone as it exists at the beginning of 1983. Ozone photochemistry in the stratosphere is discussed, taking into account fundamental molecular properties, the absorption spectrum of ozone, photodissociation, ozone formation and destruction in the upper atmosphere, the photochemistry of odd-hydrogen, the photochemistry of odd-nitrogen, the photochemistry of odd-chlorine, and photochemistry-temperature coupling. The observed distribution of atmospheric ozone and its variations are considered along with ozone transport, ozone in the troposphere, stratospheric ozone perturbations, and climatic and biological effects. Attention is given to the techniques of observing atmospheric ozone, horizontal-vertical ozone transport and conservative quantities, measurements of tropospheric ozone, the tropospheric ozone budget, ozone models, natural ozone variations, and anthropogenic ozone perturbations.
Whitten, R. C.↗
Processes Influencing Ozone Levels in Alaskan Forest Fires Plumes during Long-Range Transport over the North Atlantic
A case of long-range transport of a biomass burning plume from Alaska to Europe is analyzed using a Lagrangian approach. This plume was sampled several times in the free troposphere over North America, the North Atlantic and Europe by 3 different aircraft during the IGAC Lagrangian 2K4 experiment which was part of the ICARTT/ITOP measurement intensive in summer 2004. Measurements in the plume showed enhanced values of CO, VOCs and NOy, mainly in form of PAN. Observed O3 levels increased by 17 ppbv over 5 days. A photochemical trajectory model, CiTTyCAT, is used to examine processes responsible for the chemical evolution of the plume. The model was initialized with upwind data, and compared with downwind measurements. The influence of high aerosol loading on photolysis rates in the plume is investigated using in-situ aerosol measurements in the plume and lidar retrievals of optical depth as input into a photolysis code (Fast-J), run in the model. Significant impacts on photochemistry are found with a decrease of 18 percent in O3 production and 24 percent in O3 destruction over 5 days when including aerosols. The plume is found to be chemically active with large O3 increases attributed primarily to PAN decomposition during descent of the plume towards Europe. The predicted O3 changes are very dependent on temperature changes during transport, and also, on water vapor levels in the lower troposphere which can lead to O3 destruction. Simulation of mixing/dilution was necessary to reproduce observed pollutants level in the plume. Mixing was simulated using background concentrations from measurements in air masses in close proximity to the plume, and mixing timescales (averaging 6.25 days) were derived from CO changes. Observed and simulated O3/CO correlations in the plume are also compared in order to evaluate the photochemistry in the model. Observed slopes changed from negative to positive over 5 days. This change, which can be attributed largely to photochemistry, is well reproduced by multiple model runs even if slope values are slightly underestimated suggesting small underestimation of photochemical processes. The possible impact of this biomass burning plume on O3 levels in the Europe boundary layer is also examined by running the model for a further 5 days, and comparing with data collected at surface sites, such as Jungfraujoch, which showed small O3 increases and elevated CO levels. The model predicts significant changes in O3 over this 10 days due to photochemistry but the signal is largely lost due to the effects of dilution. However, measurement in several others BB plumes over Europe show that O3 impact of Alaskan fires can be punctually significant over Europe.
Real, E.↗
Effects of nonmethane hydrocarbons in the atmosphere
An investigation was conducted to determine whether nonmethane hydrocarbons (NMHC) are abundant enough to have a significant impact upon the ambient photochemistry. The vertical distribution of C2H6, C2H2, C3H8, C4H10, and C5H12 in the altitude range from 0 to 40 km was calculated in this connection. A one-dimensional steady state model with coupled photochemistry and vertical transport was employed in the investigation. The calculations imply that measurable quantities of relatively unreactive NMHC, especially C2H6 and C2H2, may be present in the upper troposphere and stratosphere. The results indicate, however, that NMHC are not likely to have a large impact on the background photochemistry of the troposphere, although local effects near source regions are probable. The findings support the current practice of many modelers who neglect NMHC in their calculations.
Chameides, W. L.↗
A program of research in environmental modeling
A theoretical framework for the interpretation of satellite measurements of stratospheric temperature and trace gases is provided. This problem is quite complicated since the distributions of trace gases are dependent on dynamics and photochemistry. Therefore, the problem was attacked with models employing varying degrees of photochemical and dynamical complexity. The relationship between dynamics and trace gas transport and wave transience, dissipation and critical levels and the net (permanent) transport of trace gases, the role of photochemistry in trace gas transport, photochemistry and dynamics and altering the mean-zonal distribution of stratospheric ozone, and approximations to simplify the interpretation of observations and General Circulation Models are discussed.
Source record↗
Report on the 2-D Model Intercomparison Workshop held January 11-16, 1987 in Fort Myers Beach, Florida, chapter 2
In the attempts to understand the processes which affect ozone in the stratosphere, and to predict future ozone levels, a variety of computer models were developed and employed. To oversimplify somewhat, the models range from 1-D models with intricately detailed photochemistry but only the crudest representation of transport, to 3-D general circulation models with intricately detailed dynamics and no photochemistry at all. Each of these has its appropriate uses. It was felt that there was much to be gained from intermediate models incorporating an extensive treatment of photochemistry with a dynamical framework which at least recognizes that atmospheric motions are advective as well as diffusive, and that both chemistry and dynamics are subject to latitudinal and seasonal variations. Thus the 2-D, zonally averaged models have begun to play a larger role in the last seven years, both in attempting to understand observed distributions of trace species and in attempting to assess the probable effects of antropogenic perturbations. There are many choices to be made in developing the model. It was the purpose of the 2-D model Intercomparison Workshop to permit discussion of the choices made and the behavior of the resulting models. The goal was not to identify a best set of choices, but rather to identify areas in which the models are sensitive to the choices made, and to develop a sense of where these models as a class do well or poorly in simulating the observed atmosphere.
Guthrie, Paul D.↗
Submillimeter and millimeter observations of solar system objects
Microwave spectroscopy of solar system objects was supported. It necessarily involves millimeter and submillimeter wavelengths where rotational transitions reside. The existing national facilities are at OVRO, the 12-meter at Kitt Peak, UC array at Hat Creek, the Caltech CSO on Mauna Kea, and the 14-meter at the Univ. of Massachusetts, near Amherst. The group used all of these instruments in the last year except the Univ. of Massachusetts 14-meter. This wavelength range (0.3 to 3 mm) is about to enjoy an explosion of interest as submillimeter receivers become better and easier to use. This region of the spectrum is rich in transitions of molecules that exist in the planetary atmospheres which can be studied for temperature-pressure profiles, wind tracers, and atmospheric chemistry. The list of solar system objects that have been recently addressed with these techniques include: (1) Venus: CO studies of T-P profiles, winds, and photochemistry; SO2 detections; Continuum mapping remains to be done at 1 mm; (2) Earth H2O, CO, NO, NO2, O(18)O, etc. as a test bed for other atmospheres; (3) Mars: H2O, CO, O(18)O studies of T-P profiles, winds (fall of 1990), and photochemistry; (4) Saturn: Same as Jupiter plus submillimeter and millimeter mapping of the ring system; (5) Uranus and Neptune: Continuum thermal mapping; and (6) Titan: CO, HCN, and HC3NT-P information and photochemistry. Recent results are given.
Muhleman, Duane O.↗
Origin of Ozone NO(x) in the Tropical Troposphere: A Photochemical Analysis of Aircraft Observations Over the South Atlantic Basin
The photochemistry of the troposphere over the South Atlantic basin is examined by modeling of aircraft observations up to 12-km altitude taken during the TRACE A expedition in September-October 1992. A close balance is found in the 0 to 12-km column between photochemical production and loss Of O3, with net production at high altitudes compensating for weak net loss at low altitudes. This balance implies that O3 concentrations in the 0-12 km column can be explained solely by in situ photochemistry; influx from the stratosphere is negligible. Simulation of H2O2, CH3OOH, and CH2O concentrations measured aboard the aircraft lends confidence in the computations of O3 production and loss rates, although there appears to be a major gap in current understanding of CH2O chemistry in the marine boundary layer. The primary sources of NO(x) over the South Atlantic Basin appear to be continental (biomass burning, lightning, soils). There is evidence that NO(x) throughout the 0 to 12-km column is recycled from its oxidation products rather than directly transported from its primary sources. There is also evidence for rapid conversion of HNO3 to NO(x) in the upper troposphere by a mechanism not included in current models. A general representation of the O3 budget in the tropical troposphere is proposed that couples the large scale Walker circulation and in situ photochemistry. Deep convection in the rising branches of the Walker circulation injects NO(x) from combustion, soils, and lightning to the upper troposphere, leading to O3 production; eventually, the air subsides and net O3 loss takes place in the lower troposphere, closing the O3 cycle. This scheme implies a great sensitivity of the oxidizing power of the atmosphere to NO(x) emissions in the tropics.
Jacob, D. J.↗