545 results on '"Salawitch, R. J."'
Search Results
2. Precision requirements for space-based X CO 2 data
- Author
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Miller, C. E, Crisp, D., DeCola, P. L, Olsen, S. C, Randerson, J. T, Michalak, A. M, Alkhaled, A., Rayner, P., Jacob, D. J, Suntharalingam, P., Jones, D. B. A, Denning, A. S, Nicholls, M. E, Doney, S. C, Pawson, S., Boesch, H., Connor, B. J, Fung, I. Y, O'Brien, D., Salawitch, R. J, Sander, S. P, Sen, B., Tans, P., Toon, G. C, Wennberg, P. O, Wofsy, S. C, Yung, Y. L, and Law, R. M
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atmospheric composition ,carbon dioxide ,mathematical models ,uncertainty analysis ,assessment method ,carbon dioxide ,carbon flux ,precision ,sampling ,simulation ,spatiotemporal analysis - Abstract
Precision requirements are determined for space-based column-averaged CO2 dry air mole fraction data. These requirements result from an assessment of spatial and temporal gradients in the relationship between precision and surface CO2 flux uncertainties inferred from inversions of the data, and the effects of biases on the fidelity of CO2 flux inversions. Observational system simulation experiments and synthesis inversion modeling demonstrate that the Orbiting Carbon Observatory mission design and sampling strategy provide the means to achieve these data precision requirements.
- Published
- 2007
3. A Strategy for Process-Oriented Validation of Coupled Chemistry-Climate Models
- Author
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Eyring, V., Harris, N. R. P, Rex, M., Shepherd, T. G, Fahey, D. W, Amanatidis, G. T, Austin, J., Chipperfield, M. P, Dameris, M., Forster, P. M. De F, Gettelman, A., Graf, H. F, Nagashima, T., Newman, P. A, Pawson, S., Prather, M. J, Pyle, J. A, Salawitch, R. J, Santer, B. D, and Waugh, D. W
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atmospheric chemistry ,climate change ,greenhouse effect ,mathematical models ,ozone layer ,upper atmosphere - Abstract
Accurate and reliable predictions and an understanding of future changes in the stratosphere are major aspects of the subject of climate change. Simulating the interaction between chemistry and climate is of particular importance, because continued increases in greenhouse gases and a slow decrease in halogen loading are expected. These both influence the abundance of stratospheric ozone. In recent years a number of coupled chemistry–climate models (CCMs) with different levels of complexity have been developed. They produce a wide range of results concerning the timing and extent of ozone-layer recovery. Interest in reducing this range has created a need to address how the main dynamical, chemical, and physical processes that determine the long-term behavior of ozone are represented in the models and to validate these model processes through comparisons with observations and other models. A set of core validation processes structured around four major topics (transport, dynamics, radiation, and stratospheric chemistry and microphysics) has been developed. Each process is associated with one or more model diagnostics and with relevant datasets that can be used for validation. This approach provides a coherent framework for validating CCMs and can be used as a basis for future assessments. Similar efforts may benefit other modeling communities with a focus on earth science research as their models increase in complexity.
- Published
- 2005
4. The diurnal variation of hydrogen, nitrogen, and chlorine radicals: Implications for the heterogeneous production of HNO 2
- Author
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Salawitch, R. J, Wofsy, S. C, Wennberg, P. O, Cohen, R. C, Anderson, J. G, Fahey, D. W, Gao, R. S, Keim, E. R, Woodbridge, E. L, Stimpfle, R. M, Koplow, J. P, Kohn, D. W, Webster, C. R, May, R. D, Pfister, L., Gottlieb, E. W, Michelsen, H. A, Yue, G. K, Prather, M. J, Wilson, J. C, Brock, C. A, Jonsson, H. H, Dye, J. E, Baumgardner, D., Proffitt, M. H, Loewenstein, M., Podolske, J. R, Elkins, J. W, Dutton, G. S, Hintsa, E. J, Dessler, A. E, Weinstock, E. M, Kelly, K. K, Boering, K. A, Daube, B. C, Chan, K. R, and Bowen, S. W
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environmental chambers ,peroxynitric acid ,stratosphere - Abstract
In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained through sunrise and sunset in the lower stratosphere during SPADE are compared to results from a photochemical model constrained by observed concentrations of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N2O5 on sulfate aerosols agree with measured concentrations of NO, NO2, and ClO throughout the day, but fail to account for high concentrations of OH and HO2 observed near sunrise and sunset. The morning burst of [OH] and [HO2] coincides with the rise of [NO] from photolysis of NO2, suggesting a new source of HOxthat photolyzes in the near UV (350 to 400 nm) spectral region. A model that allows for the heterogeneous production of HNO2 results in an excellent simulation of the diurnal variations of [OH] and [HO2].
- Published
- 1994
5. Link Between Arctic Tropospheric BrO Explosion Observed from Space and Sea-Salt Aerosols from Blowing Snow Investigated Using Ozone Monitoring Instrument BrO Data and GEOS-5 Data Assimilation System
- Author
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Choi, S, Theys, N, Salawitch, R. J, Wales, P. A, Joiner, J, Canty, T. P, Chance, K, Suleiman, R. M, Palm, S. P, Cullather, R. I, Darmenov, A. S, da Silva, A, Kurosu, T. P, Hendrick, F, and Van Roozendael, M
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Earth Resources And Remote Sensing - Abstract
Bromine radicals (Br + BrO) are important atmospheric species owing to their ability to catalytically destroy ozone as well as their potential impacts on the oxidative pathways of many trace gases, including dimethylsulfide and mercury. Using space-based observations of BrO, recent studies have reported rapid enhancements of tropospheric BrO over large areas (so called "BrO explosions") connected to near-surface ozone depletion occurring in polar spring. However, the source(s) of reactive bromine and mechanism(s) that initiate these BrO explosions are uncertain. In this study, we investigate the relationships between Arctic BrO explosions and two of the proposed sources of reactive bromine: sea-salt aerosol (SSA) generated from blowing snow and first-year (seasonal) sea ice. We use tropospheric column BrO derived from the Ozone Monitoring Instrument (OMI) in conjunction with the Goddard Earth Observing System Version 5 (GEOS-5) data assimilation system provided by National Aeronautics and Space Administration Global Modeling and Assimilation Office. Case studies demonstrate a strong association between the temporal and spatial extent of OMI-observed BrO explosions and the GEOS-5 simulated blowing snow-generated SSA during Arctic spring. Furthermore, the frequency of BrO explosion events observed over the 11-year record of OMI exhibits significant correlation with a time series of the simulated SSA emission flux in the Arctic and little to no correlation with a time series of satellite-based first-year sea ice area. Therefore, we conclude that SSA generated by blowing snow is an important factor in the formation of the BrO explosion observed from space during Arctic spring.
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- 2018
- Full Text
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6. Reduced Complexity Model Intercomparison Project Phase 2: Synthesizing Earth System Knowledge for Probabilistic Climate Projections
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Nicholls, Z., primary, Meinshausen, M., additional, Lewis, J., additional, Corradi, M. Rojas, additional, Dorheim, K., additional, Gasser, T., additional, Gieseke, R., additional, Hope, A. P., additional, Leach, N. J., additional, McBride, L. A., additional, Quilcaille, Y., additional, Rogelj, J., additional, Salawitch, R. J., additional, Samset, B. H., additional, Sandstad, M., additional, Shiklomanov, A., additional, Skeie, R. B., additional, Smith, C. J., additional, Smith, S. J., additional, Su, X., additional, Tsutsui, J., additional, Vega‐Westhoff, B., additional, and Woodard, D. L., additional
- Published
- 2021
- Full Text
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7. Reduced Complexity Model Intercomparison Project Phase 2: Synthesizing Earth System Knowledge for Probabilistic Climate Projections
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Nicholls, Z., Meinshausen, M., Lewis, J., Corradi, M. Rojas, Dorheim, K., Gasser, T., Gieseke, R., Hope, A. P., Leach, N. J., McBride, L. A., Quilcaille, Y., Rogelj, J., Salawitch, R. J., Samset, B. H., Sandstad, M., Shiklomanov, A., Skeie, R. B., Smith, C., Smith, S. J., Su, X., Tsutsui, J., Vega‐Westhoff, B., Woodard, D. L., Nicholls, Z., Meinshausen, M., Lewis, J., Corradi, M. Rojas, Dorheim, K., Gasser, T., Gieseke, R., Hope, A. P., Leach, N. J., McBride, L. A., Quilcaille, Y., Rogelj, J., Salawitch, R. J., Samset, B. H., Sandstad, M., Shiklomanov, A., Skeie, R. B., Smith, C., Smith, S. J., Su, X., Tsutsui, J., Vega‐Westhoff, B., and Woodard, D. L.
- Abstract
Over the last decades, climate science has evolved rapidly across multiple expert domains. Our best tools to capture state-of-the-art knowledge in an internally self-consistent modeling framework are the increasingly complex fully coupled Earth System Models (ESMs). However, computational limitations and the structural rigidity of ESMs mean that the full range of uncertainties across multiple domains are difficult to capture with ESMs alone. The tools of choice are instead more computationally efficient reduced complexity models (RCMs), which are structurally flexible and can span the response dynamics across a range of domain-specific models and ESM experiments. Here we present Phase 2 of the Reduced Complexity Model Intercomparison Project (RCMIP Phase 2), the first comprehensive intercomparison of RCMs that are probabilistically calibrated with key benchmark ranges from specialized research communities. Unsurprisingly, but crucially, we find that models which have been constrained to reflect the key benchmarks better reflect the key benchmarks. Under the low-emissions SSP1-1.9 scenario, across the RCMs, median peak warming projections range from 1.3 to 1.7°C (relative to 1850–1900, using an observationally based historical warming estimate of 0.8°C between 1850–1900 and 1995–2014). Further developing methodologies to constrain these projection uncertainties seems paramount given the international community's goal to contain warming to below 1.5°C above preindustrial in the long-term. Our findings suggest that users of RCMs should carefully evaluate their RCM, specifically its skill against key benchmarks and consider the need to include projections benchmarks either from ESM results or other assessments to reduce divergence in future projections.
- Published
- 2021
8. The NOx-HNO3 system in the lower stratosphere: Insights from in situ measurements and implications of J(sub HNO3)-[OH] relationship
- Author
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Perkins, K. K., Koch, L. C., Bonne, G. P., Wennberg, P. O., Salawitch, R. J., McElroy, C. T., Cohen, R. C., Hanisco, T. F., Hinsta, E. J., Voss, P. B., Stimpfle, R. M., Anderson, J. G., Lanzendorf, E. J., Del Negro, L. A., Gao, R. S., Bui, T. P., and Loewenstein, M.
- Subjects
Photolysis -- Methods ,Stratosphere -- Research ,Nitric acid -- Research ,Chemicals, plastics and rubber industries - Abstract
The situ observations were used to evaluate the primary mechanisms that control NOx-HNO3 exchange and to understand their control over the partitioning between NO2 and HNO3 in regions of continuous sunlight. The steady-state description of NOx-HNO3 exchange reveals the significant influence of the tight correlation between the photolysis rate of HNO3 and [OH] established in situ measurements throughout the lower stratosphere.
- Published
- 2001
9. Sources, sinks, and the distribution of OH in the lower stratosphere
- Author
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Hanisco, T. F., Perkins, K. K., Anderson, J. G., Gao, R. S., Margitan, J. J., Wennberg, P. O., Lanzendorf, E. J., Voss, P. B., Stimpfle, R. M., Fahey, D., Cohen, R. C., Salawitch, R. J., Hintsa, E. J., Midwinter, C., and McElroy, C. T.
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United States. National Aeronautics and Space Administration -- Research ,Hydroxylation -- Research ,Stratosphere -- Research ,Chemicals, plastics and rubber industries - Abstract
The extensive measurement campaigns by the NASA ER-2 research aircraft have obtained a nearly pole-to-pole database of the species that control HOx (OH + HO2) chemistry. The measurements in the lower stratosphere shows a remarkably tight correlation of OH concentration with the solar zenith angle (SZA).
- Published
- 2001
10. Fluxes of Atmospheric Greenhouse‐Gases in Maryland (FLAGG‐MD): Emissions of Carbon Dioxide in the Baltimore, MD‐Washington, D.C. Area
- Author
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Ahn, D. Y., primary, Hansford, J. R., additional, Howe, S. T., additional, Ren, X. R., additional, Salawitch, R. J., additional, Zeng, N., additional, Cohen, M. D., additional, Stunder, B., additional, Salmon, O. E., additional, Shepson, P. B., additional, Gurney, K. R., additional, Oda, T., additional, Lopez‐Coto, I., additional, Whetstone, J., additional, and Dickerson, R. R., additional
- Published
- 2020
- Full Text
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11. Analysis of Satellite-Derived Arctic Tropospheric BrO Columns in Conjunction with Aircraft Measurements During ARCTAS and ARCPAC
- Author
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Choi, S, Wang, Y, Salawitch, R. J, Canty, T, Joiner, J, Zeng, T, Kurosu, T. P, Chance, K, Richter, A, Huey, L. G, Liao, J, Neuman, J. A, Nowak, J. B, Dibb, J. E, Weinheimer, A. J, Diskin, G, Ryerson, T. B, da Silva, A, Curry, J, Kinnison, D, Tilmes, S, and Levelt, P. F
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Geophysics - Abstract
We derive tropospheric column BrO during the ARCTAS and ARCPAC field campaigns in spring 2008 using retrievals of total column BrO from the satellite UV nadir sensors OMI and GOME-2 using a radiative transfer model and stratospheric column BrO from a photochemical simulation. We conduct a comprehensive comparison of satellite-derived tropospheric BrO column to aircraft in-situ observations ofBrO and related species. The aircraft profiles reveal that tropospheric BrO, when present during April 2008, was distributed over a broad range of altitudes rather than being confined to the planetary boundary layer (PBL). Perturbations to the total column resulting from tropospheric BrO are the same magnitude as perturbations due to longitudinal variations in the stratospheric component, so proper accounting of the stratospheric signal is essential for accurate determination of satellite-derived tropospheric BrO. We find reasonably good agreement between satellite-derived tropospheric BrO and columns found using aircraft in-situ BrO profiles, particularly when satellite radiances were obtained over bright surfaces (albedo> 0.7), for solar zenith angle < 80 and clear sky conditions. The rapid activation of BrO due to surface processes (the bromine explosion) is apparent in both the OMI and GOME-2 based tropospheric columns. The wide orbital swath of OMI allows examination of the evolution of tropospheric BrO on about hourly time intervals near the pole. Low surface pressure, strong wind, and high PBL height are associated with an observed BrO activation event, supporting the notion of bromine activation by high winds over snow.
- Published
- 2012
12. Multimodel Assessment of the Factors Driving Stratospheric Ozone Evolution over the 21st Century
- Author
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Oman, L. D, Plummer, D. A, Waugh, D. W, Austin, J, Scinocca, J. F, Douglass, A. R, Salawitch, R. J, Canty, T, Akiyoshi, H, Bekki, S, Braesicke, P, Butchart, N, Chipperfield, M. P, Cugnet, D, Dhomse, S, Eyring, V, Frith, S, Hardiman, S. C, Kinnison, D. E, Lamarque, J.-F, Mancini, E, Marchand, M, Michou, M, Morgenstern, O, and Nakamura, T
- Subjects
Geophysics - Abstract
The evolution of stratospheric ozone from 1960 to 2100 is examined in simulations from 14 chemistry-climate models, driven by prescribed levels of halogens and greenhouse gases. There is general agreement among the models that total column ozone reached a minimum around year 2000 at all latitudes, projected to be followed by an increase over the first half of the 21st century. In the second half of the 21st century, ozone is projected to continue increasing, level off, or even decrease depending on the latitude. Separation into partial columns above and below 20 hPa reveals that these latitudinal differences are almost completely caused by differences in the model projections of ozone in the lower stratosphere. At all latitudes, upper stratospheric ozone increases throughout the 21st century and is projected to return to 1960 levels well before the end of the century, although there is a spread among models in the dates that ozone returns to specific historical values. We find decreasing halogens and declining upper atmospheric temperatures, driven by increasing greenhouse gases, contribute almost equally to increases in upper stratospheric ozone. In the tropical lower stratosphere, an increase in upwelling causes a steady decrease in ozone through the 21st century, and total column ozone does not return to 1960 levels in most of the models. In contrast, lower stratospheric and total column ozone in middle and high latitudes increases during the 21st century, returning to 1960 levels well before the end of the century in most models.
- Published
- 2010
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13. Multi-Model Assessment of the Factors Driving Stratospheric Ozone Evolution Over the 21st Century
- Author
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Oman, L. D, Plummer, D. A, Waugh, D. W, Austin, J, Scinocca, J, Douglass, A. R, Salawitch, R. J, Canty, T, Akiyoshi, H, Bekki, S, Braesicke, P, Butchart, N, Chipperfield, M. P, Cugnet, D, Dhomse, S, Eyring, V, Frith, S, Hardiman, S. C, Kinnison, D. E, Lamarque, J. F, Mancini, E, Marchand, M, Michou, M, Morgenstern, O, and Nakamura T
- Subjects
Meteorology And Climatology - Abstract
The evolution of stratospheric ozone from 1960 to 2100 is examined in simulations from fourteen chemistry-climate models. There is general agreement among the models at the broadest levels, showing column ozone decreasing at all latitudes from 1960 to around 2000, then increasing at all latitudes over the first half of the 21st century, and latitudinal variations in the rate of increase and date of return to historical values. In the second half of the century, ozone is projected to continue increasing, level off or even decrease depending on the latitude, resulting in variable dates of return to historical values at latitudes where column ozone has declined below those levels. Separation into partial column above and below 20 hPa reveals that these latitudinal differences are almost completely due to differences in the lower stratosphere. At all latitudes, upper stratospheric ozone increases throughout the 21st century and returns to 1960 levels before the end of the century, although there is a spread among the models in dates that ozone returns to historical values. Using multiple linear regression, we find decreasing halogens and increasing greenhouse gases contribute almost equally to increases in the upper stratospheric ozone. In the tropical lower stratosphere an increase in tropical upwelling causes a steady decrease in ozone through the 21st century, and total column ozone does not return to 1960 levels in all models. In contrast, lower stratospheric and total column ozone in middle and high latitudes increases during the 21st century and returns to 1960 levels.
- Published
- 2010
14. Observed and Modeled HOCl Profiles in the Midlatitude Stratosphere: Implication for Ozone Loss
- Author
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Kovalenko, L. J, Jucks, K. W, Salawitch, R. J, Toon, G. C, Blavier, J. F, Johnson, D. G, Kleinbohl, A, Livesey, N. J, Margitan, J. J, Pickett, H. M, Santee, M. L, Sen, B, Stachnik, R. A, and Waters, J. W
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Meteorology And Climatology - Abstract
Vertical profiles of stratospheric HOCl calculated with a diurnal steady-state photochemical model that uses currently recommended reaction rates and photolysis cross sections underestimate observed profiles of HOCl obtained by two balloon-borne instruments, FIRS-2 (a far-infrared emission spectrometer) and MkIV (a mid-infrared, solar absorption spectrometer). Considerable uncertainty (a factor of two) persists in laboratory measurements of the rate constant (k(sub 1)) for the reaction ClO + HO2 yields HOCl + O2. Agreement between modeled and measured HOCl can be attained using a value of k(sub 1) from Stimpfle et al. (1979) that is about a factor-of-two faster than the currently recommended rate constant. Comparison of modeled and measured HOCl suggests that models using the currently recommended value for k(sub 1) may underestimate the role of the HOCl catalytic cycle for ozone depletion, important in the midlatitude lower stratosphere.
- Published
- 2007
- Full Text
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15. Future changes in upper stratospheric ozone
- Author
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Jucks, K. W., primary and Salawitch, R. J., additional
- Published
- 2000
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16. Quantifying transport between the tropical and mid-latitude lower stratosphere
- Author
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Volk, C. M., Elkins, J. W., Fahey, D. W., Salawitch, R. J., Dutton, G. S., Gilligan, J. M., Proffitt, M. H., Loewenstein, M., Podolske, J. R., Minschwaner, K., Margitan, J.J., and Chan, K.R.
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Supersonic planes -- Environmental aspects -- Research ,Atmospheric research -- Observations -- Environmental aspects -- Research ,Stratospheric circulation -- Research -- Environmental aspects ,Science and technology ,Observations ,Research ,Environmental aspects - Abstract
Airborne in situ observations of molecules with a wide range of lifetimes (methane, nitrous oxide, reactive nitrogen, ozone, chlorinated halocarbons, and halon-1211), used in a tropical tracer model, show that mid-latitude air is entrained into the tropical lower stratosphere within about 13.5 months; transport is faster in the reverse direction. Because exchange with the tropics is slower than global photochemical models generally assume, ozone at mid-latitudes appears to be more sensitive to elevated levels of industrial chlorine than is currently predicted. Nevertheless, about 45 percent of air in the tropical ascent region at 21 kilometers is of mid-latitude origin, implying that emissions from supersonic aircraft could reach the middle stratosphere., Tropospheric air enters the stratosphere predominantly at the tropical tropopause and is then dispersed upward and toward the poles. In the tropics, stratospheric air is lofted most efficiently, and photochemistry [...]
- Published
- 1996
17. Temporal Decrease in Upper Atmospheric Chlorine
- Author
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Froidevaux, L, Livesey, N. J, Read, W. G, Salawitch, R. J, Waters, J. W, Drouin, B, MacKenzie, I. A, Pumphrey, H. C, Bernath, P, Boone, C, Nassar, R, Montzka, S, Elkins, J, Cunnold, D, and Waugh, D
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Chemistry And Materials (General) - Abstract
We report a steady decrease in the upper stratospheric and lower mesospheric abundances of hydrogen chloride (HCl) from August 2004 through January 2006, as measured by the Microwave Limb Sounder (MLS) aboard the Aura satellite. For 60(deg)S to 60(deg)N zonal means, the average yearly change in the 0.7 to 0.1 hPa (approx.50 to 65 km) region is -27 +/- 3 pptv/year, or -0.78 +/- 0.08 percent/year. This is consistent with surface abundance decrease rates (about 6 to 7 years earlier) in chlorine source gases. The MLS data confirm that international agreements to reduce global emissions of ozone-depleting industrial gases are leading to global decreases in the total gaseous chlorine burden. Tracking stratospheric HCl variations on a seasonal basis is now possible with MLS data. Inferred stratospheric total chlorine (CITOT) has a value of 3.60 ppbv at the beginning of 2006, with a (2-sigma) accuracy estimate of 7%; the stratospheric chlorine loading has decreased by about 43 pptv in the 18-month period studied here. We discuss the MLS HCl measurements in the context of other satellite-based HCl data, as well as expectations from surface chlorine data. A mean age of air of approx. 5.5 years and an age spectrum width of 2 years or less provide a fairly good fit to the ensemble of measurements.
- Published
- 2006
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18. Toward a Better Quantitative Understanding of Polar Stratospheric Ozone Loss
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Frieler, K, Rex, M, Salawitch, R. J, Canty, T, Streibel, M, Stimpfle, R. M, Pfeilsticker, K, Dorf, M, Weisenstein, D. K, and Godin-Beekmann, S
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Geophysics - Abstract
Previous studies have shown that observed large O3 loss rates in cold Arctic Januaries cannot be explained with current understanding of the loss processes, recommended reaction kinetics, and standard assumptions about total stratospheric chlorine and bromine. Studies based on data collected during recent field campaigns suggest faster rates of photolysis and thermal decomposition of ClOOCl and higher stratospheric bromine concentrations than previously assumed. We show that a model accounting for these kinetic changes and higher levels of BrO can largely resolve the January Arctic O3 loss problem and closely reproduces observed Arctic O3 loss while being consistent with observed levels of ClO and ClOOCl. The model also suggests that bromine catalyzed O3 loss is more important relative to chlorine catalyzed loss than previously thought.
- Published
- 2006
- Full Text
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19. Quantifying Stratospheric Ozone in the Upper Troposphere with in Situ Measurements of HCl
- Author
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Marcy, T. P., Fahey, D. W., Gao, R. S., Popp, P. J., Richard, E. C., Thompson, T. L., Rosenlof, K. H., Ray, E. A., Salawitch, R. J., Atherton, C. S., Bergmann, D. J., Ridley, B. A., Weinheimer, A. J., Loewenstein, M., Weinstock, E. M., and Mahoney, M. J.
- Published
- 2004
20. Change in ozone trends at southern high latitudes
- Author
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Yang, E.-S, Cunnold, D. M, Newchurch, M. J, and Salawitch, R. J
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Geophysics - Abstract
Long-term ozone variations at 60-70degS in spring are investigated using ground-based and satellite measurements. Strong positive correlation is shown between year-to-year variations of ozone and temperature in the Antarctic collar region in Septembers and Octobers. Based on this relationship, the effect of year-to-year variations in vortex dynamics has been filtered out. This process results in an ozone time series that shows increasing springtime ozone losses over the Antarctic until the mid-1990s. Since approximately 1997 the ozone losses have leveled off. The analysis confirms that this change is consistent across all instruments and is statistically significant at the 95% confidence level. This analysis quantifies the beginning of the recovery of the ozone hole, which is expected from the leveling off of stratospheric halogen loading due to the ban on CFCs and other halocarbons initiated by the Montreal Protocol.
- Published
- 2005
21. Sensitivity of ozone to bromine in the lower stratosphere
- Author
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Salawitch, R. J, Weisenstein, D. K, Kovalenko, L. J, Sioris, C. E, Wennberg, P. O, Chance, K, Ko, M. K. W, and McLinden, C. A
- Published
- 2005
22. Nighttime OClO in the Winter Arctic Vortex
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Canty, T, Riviere, E. D, Salawitch, R. J, Berthet, G, Renard, J. -B, Pfeilsticker, K, Dorf, M, Butz, A, Bosch, H, Stimpfle, R. M, Wilmouth, D. M, Richard, E. C, Fahey, D. W, Popp, P. J, Schoeberl, M. R, Lait, L. R, and Bui, T. P
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Chemistry And Materials (General) - Abstract
We show that a nighttime profile of OClO in the Arctic vortex during the winter of 2000 is overestimated, by nearly a factor of 2, using an isentropic trajectory model constrained by observed profiles of ClOx (ClO + 2 X ClOOCl) and BrO. Calculated abundances of nighttime OClO are shown to be sensitive to the abundance of BrOx (BrO + BrCl), details of the air parcel history during the most recent sunrise/sunset transitions, and the BrCl yield from the reaction BrO + ClO. Many uncertainties are considered, and the discrepancy between measured and modeled nighttime OClO appears to be robust. This discrepancy suggests that production of OClO occurs more slowly than implied by standard photochemistry. If the yield of BrCl from the reaction of BrO + ClO is increased from 7% (JPL 2002 value) to 11% (near the upper limit of the uncertainty), good agreement is found between measured and modeled nighttime OClO. This study highlights the importance of accurate knowledge of BrO + ClO reaction kinetics as well as air parcel trajectories for proper interpretation of nighttime OClO. These factors have a considerably smaller impact on the interpretation of OClO observations obtained during twilight (90(deg) <=SZA <= 92(deg)), when photolytic processes are still active.
- Published
- 2005
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23. Measured and modeled HOCl profiles in the mid-latitude stratosphere : implication for ozone loss
- Author
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Kovalenko, L. J, Salawitch, R. J, Blavier, J. -F, Sen, B, Toon, G. C, Jucks, K. W, Johnson, D. G, Stachnik, R. A, and Margitan, J. J
- Abstract
The HOCl catalytic cycle is an efficient ozone loss mechanism in the lower mid-latitude stratosphere. We use a diurnal steady-state photochemical model to calculate profiles of HOCl for conditions encountered by a number of high-altitude balloon flights. To assess how well this model represents ozone loss by the HOCl cycle, we compare our calculations of HOCl and its precursors Cl0 and HO2 with measurements obtained by an FTIR solar absorption spectrometer (MkIV), a far-infrared emission spectrometer (FIRS-2), and a submillimetenvave limb sounder (SLS). We then evaluate these comparisons in light of a number of recent laboratory studies of the main formation mechanism of HOCl, the reaction of Cl0 + HO2. Those studies measured both the reaction rate constant and the quantum yield for a second product pathway, formation of HCl.
- Published
- 2004
24. In situ measurements constraining the role of sulphate aerosols in mid-latitude ozone depletion
- Author
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Fahey, D.W., Kawa, S.R., Woodbridge, E.L., Tin, P., Wilson, J.C., Jonsson, H.H., Dye, J.E., Baumgardner, D., Bormann, S., Toohey, D.W., Avallone, L.M., Proffitt, M.H., Margitan, J., Loewenstein, M., Podolske, J.R., Salawitch, R. J., Wofsy, S.C., Ko, M.K.W., Anderson, D.E., Schoeberl, M.R., and Chan, K.R.
- Subjects
Ozone layer depletion -- Research ,Aerosols -- Environmental aspects ,Atmospheric research -- Reports ,Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
The relation between the atmospheric concentration of sulphate aerosols and ozone depletion at mid-latitude levels was investigated. In situ measurements of NO and NOy were performed along with aerosol surface area, namely O3 and ClO. All the measurements were conducted simultaneously at mid-latitudes in the lower stratosphere. Results show that the influence of aerosol reactions on active nitrogen is strongly dependent on the gas phase reaction rates.
- Published
- 1993
25. ER-2 measurements of CIO and CIOOCI: implications for theory and observation of ozone loss
- Author
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Salawitch, R. J, Stimpfle, R. M, Wilmouth, D. M, Anderson, J. G, and Canty, T
- Published
- 2003
26. The Detection of Large HNO3-Containing Particles in the Winter Arctic Stratosphere
- Author
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Fahey, D. W., Gao, R. S., Carslaw, K. S., Kettleborough, J., Popp, P. J., Northway, M. J., Holecek, J. C., Ciciora, S. C., McLaughlin, R. J., Thompson, T. L., Winkler, R. H., Baumgardner, D. G., Gandrud, B., Wennberg, P. O., Dhaniyala, S., McKinney, K., Peter, Th., Salawitch, R. J., Bui, T. P., Elkins, J. W., Webster, C. R., Atlas, E. L., Jost, H., Wilson, J. C., Herman, R. L., Kleinböhl, A., and von König, M.
- Published
- 2001
27. Stratospheric photochemistry
- Author
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Salawitch, R. J and Wennberg, P. O
- Published
- 2002
28. Chemistry and Transport In a Multi-Dimensional Model
- Author
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Yung, Yuk L, Allen, M, Zurek, R. W, and Salawitch, R. J
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Geophysics - Abstract
The focus of the work funded under this proposal is the exchange between the stratosphere and the troposphere, and between the troposphere and the blaspheme. These two interfaces represent the frontiers of atmospheric chemistry. It is the combination of exchange processes at both interfaces that ultimately controls how the blaspheme (including human activities) affects the ozone layer. The modeling work was motivated by and attempts to integrate information obtained by aircraft, spacecraft, shuttle and oceanic measurements. The model development and research activities accomplished in the past three years provide a technical and intellectual basis for the research in this group. The innovative part of our research program is related to the IAV of ozone and the hydrological cycle. Other related but independently supported work include the study of isotopic fractionation of atmospheric species, e.g., N2O and CO2. Our theory suggests that we now have the ability to probe the middle atmosphere at a level of sensitivity where subtle details such as the isotopic composition of simple molecules can yield measurable systematic effects. This creates the possibility for probing the chemistry and dynamics of the middle atmosphere using all of the N2O and CO2 isotopologues. In the following we will briefly describe the model development and review the highlights of recent accomplishments.
- Published
- 2002
29. Theory and observation of chemical loss of Arctic ozone during the winter of 1999-2000
- Author
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Salawitch, R. J
- Published
- 2001
30. The effect of Pinatubo aerosols on the partitioning of inorganic chlorine species
- Author
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Salawitch, R. J, Osterman, G. B, Sen, B, and Toon, G. C
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Geophysics - Published
- 2001
31. Upper tropospheric nitrogen oxides measured by solar absorption spectrometry
- Author
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Sen, B, Irion, F. W, Salawitch, R. J, and Toon, G. C
- Subjects
Meteorology And Climatology - Published
- 2001
32. Inorganic Chlorine Partitioning in the Summer Lower Stratosphere: Modeled and Measured [ClONO2/HCl] During POLARIS
- Author
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Voss, P. B, Stimpfle, R. M, Cohen, R. C, Hanisco, T. F, Bonne, G. P, Perkins, K. K, Lanzendorf, E. J, Anderson, J. G, and Salawitch, R. J
- Subjects
Geophysics - Abstract
We examine inorganic chlorine (Cly) partitioning in the summer lower stratosphere using in situ ER-2 aircraft observations made during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) campaign. New steady state and numerical models estimate [ClONO2]/[HCl] using currently accepted photochemistry. These models are tightly constrained by observations with OH (parameterized as a function of solar zenith angle) substituting for modeled HO2 chemistry. We find that inorganic chlorine photochemistry alone overestimates observed [ClONO2]/[HCl] by approximately 55-60% at mid and high latitudes. On the basis of POLARIS studies of the inorganic chlorine budget, [ClO]/[ClONO2], and an intercomparison with balloon observations, the most direct explanation for the model-measurement discrepancy in Cly partitioning is an error in the reactions, rate constants, and measured species concentrations linking HCl and ClO (simulated [ClO]/[HCl] too high) in combination with a possible systematic error in the ER-2 ClONO2 measurement (too low). The high precision of our simulation (+/-15% 1-sigma for [ClONO2]/[HCl], which is compared with observations) increases confidence in the observations, photolysis calculations, and laboratory rate constants. These results, along with other findings, should lead to improvements in both the accuracy and precision of stratospheric photochemical models.
- Published
- 2001
- Full Text
- View/download PDF
33. Measurements of HNO(sub 4): implications for HO(sub x)
- Author
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Salawitch, R. J, Sen, B, Toon, G. C, Wennberg, P. O, Osterman, G. B, and Margitan, J. J
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Geophysics - Published
- 2001
34. Measurements of HNO***sub4***: implications for HO***subX***
- Author
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Salawitch, R. J, Sen, B, Toon, G. C, Wennberg, P. O, Osterman, G. B, and Margitan, J. J
- Published
- 2001
35. An Examination of the Inorganic Chlorine Budget in the Lower Stratosphere
- Author
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Bonne, G. P, Stimpfle, R. M, Cohen, R. C, Voss, P. B, Perkins, K. K, Anderson, J. G, Salawitch, R. J, Elkins, J. W, Dutton, G. S, and Jucks, K. W
- Subjects
Geophysics - Abstract
We use the first simultaneous in situ measurements of ClONO2, ClO, and HCl acquired using the NASA ER-2 aircraft during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission to test whether these three compounds quantitatively account for total inorganic chlorine (Cly) in the lower stratosphere in 1997. We find (ClO + ClONO2 + HCl)/Cly = 0.92 +/- 0.10, where Cly is inferred from in situ measurements of organic chlorine source gases. These observations are consistent with our current understanding of the budget and partitioning of Cly in the lower stratosphere. We find no evidence in support of missing inorganic chlorine species that compose a significant fraction of Cly. We apply the analysis to earlier ER-2 observations dating from 1991 to investigate possible causes of previously observed discrepancies in the inorganic chlorine budget. Using space shuttle, satellite, balloon, and aircraft measurements in combination with ER-2 data, we find that the discrepancy is unlikely to have been caused by missing chlorine species or an error in the photolysis rate of chlorine nitrate. We also find that HCl/Cly is not significantly controlled by aerosol surface area density in the lower stratosphere.
- Published
- 2000
- Full Text
- View/download PDF
36. The Coupling of ClONO2, ClO, and NO2 in the Lower Stratosphere From in Situ Observations Using the NASA ER-2 Aircraft
- Author
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Stimpfle, R. E, Cohen, R. C, Bonne, G. P, Voss, P. B, Perkins, K. K, Koch, L. C, Anderson, J. G, Salawitch, R. J, and Gao, R. S
- Subjects
Geophysics - Abstract
The first in situ measurements of ClONO2 in the lower stratosphere, acquired using the NASA ER-2 aircraft during the Polar Ozone Loss in the Arctic Region in Summer (POLARIS) mission, are combined with simultaneous measurements of ClO, NO2, temperature, pressure, and the calculated photolysis rate coefficient (J(sub ClONO2)) to examine the balance between production and loss of ClONO2. The observations demonstrate the ClONO2 photochemical steady state measurement, [ClONO2](sup PSS) = k[ClO][No2]/J(sub ClONO2), is in good agreement with the direct measurement, [ClONO2](sup MEAS). For the bulk of the data (80%), where T > 220 K and latitudes > 45 N, [ClONO2](sup PPS) = 1.15 +/- 0.36(1-sigma)[ClONO2](sup MEAS), while for T< 220 K and latitudes < 45 N, the result is somewhat less at 1.01 +/- 0.30. The cause of the temperature and/or latitude trend is unidentified. These results are independent of solar zenith angle and air density, thus there is no evidence in support of a pressure-dependent quantum yield for photodissociation of ClONO2 at wavelengths > 300 nm. These measurements confirm the mechanism by which active nitrogen (NOx = NO + NO2) controls the abundance of active chlorine (Clx = ClO + Cl) in the stratosphere.
- Published
- 1999
- Full Text
- View/download PDF
37. The Budget and Partitioning of Stratospheric Chlorine During the 1997 Arctic Summer
- Author
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Sen, B, Osterman, G. B, Salawitch, R. J, Toon, G. C, Marigitan, J. J, Blavier, J.-F, Chang, A. Y, May, R. D, Webster, C. R, and Stimpfle, R. M
- Subjects
Geophysics - Abstract
Volume mixing ratio profiles of HCl, HOCl, ClNO3, CH3Cl, CFC-12, and CFC-11, CCl4, HCFC-22, and CFC-113 were measured simultaneously from 9 to 38 km by the Jet Propulsion Laboratory MkIV Fourier Transform Infrared solar absorption spectrometer during two balloon flights from Fairbanks, Alaska (64.8 N), on May 8 and July 8, 1997. The altitude variation of total organic chlorine (CCl(sub y)), total inorganic chlorine (Cl(sub y)), and the nearly constant value (3.7 +/- 0.2 ppbv) of their sum (Cl(sub TOT)) demonstrates that the stratospheric chlorine species available to react with O3 are supplied by the decomposition of organic chlorinated compounds whose abundances are well quantified. Measured profiles of HCl and ClNO3 agree well with profiles found by photochemical model (differences < 10% for altitudes below 35 km) constrained by various other constituents measured by MkIV. The production of HCl by ClO + OH plays a relatively small role in the partitioning of HCl and ClNO3 for the sampled air masses. However, better agreement with the measured profiles of HCl and ClNO3 is obtained when this source of HCl is included in the model. Both the measured and calculated [ClNO3]/[HCl] ratios exhibit the expected near linear variation with [O3](sup 2)/[CH4] over a broad range of altitudes. MkIV measurements of HCl, ClNO3, and CCl(sub y) agree well with ER-2 in situ observations of these quantities for directly comparable air masses. These results demonstrate good understanding of the budget of stratospheric chlorine and that the partitioning of inorganic chlorine is accurately described by photochemical models that employ JPL97 reaction rates and production of HCl from ClO + OH for the environmental conditions encountered: relatively warm temperatures, long periods of solar illumination, and relatively low aerosol surface areas.
- Published
- 1999
- Full Text
- View/download PDF
38. Polar Stratospheric Descent of NO(y) and CO and Arctic Denitrification During Winter 1992-1993
- Author
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Rinsland, C. P, Salawitch, R. J, Gunson, M. R, Solomon, S, Zander, R, Mahieu, E, Goldman, A, Newchurch, M. J, Irion, F. W, and Chang, A. Y
- Subjects
Environment Pollution - Abstract
Observations inside the November 1994 Antarctic stratospheric vortex and inside the April 1993 remnant Arctic stratospheric vortex by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer are reported. In both instances, elevated volume mixing ratios (VMRS) of carbon monoxide (CO) were measured. A peak Antarctic CO VMR of 60 ppbv (where 1 ppbv = 10(exp -9) per unit Volume) was measured at a potential temperature of 710 K (about 27 km), about 1 km below the altitude of a pocket of elevated NO(y) (total reactive nitrogen) at a deep minimum in N2O (<5 ppbv). The Arctic observations also show a region of elevated vortex CO with a peak VMR of 90 ppbv it 630-670 K (-25 km) but no corresponding enhancement in NO(sub y) perhaps because of stronger dynamical activity in the northern hemisphere polar winter and/or interannual variability in the production of mesospheric or lower thermospheric NO. By comparing vortex and extravortex observations of NO(y) obtained at the same N2O VMR, Arctic vortex denitrification of 5 +/- 2 ppbv at 470 K (at approximately 18 km) is inferred. We show that our conclusion of substantial Arctic winter 1992-1993 denitrification is robust by comparing our extravortex observations with previous polar measurements obtained over a wide range of winter conditions. Correlations of NO(y) with N2O measured at the same potential temperature by ATMOS in the Arctic vortex and at midlatitudes on board the ER-2 aircraft several weeks later lie along the same mixing line. The result demonstrates the consistency of the two data sets and confirms that the ER-2 sampled fragments of the denitrified Arctic vortex following its breakup. An analysis of the ATMOS Arctic measurements of total hydrogen shows no evidence for significant dehydration inside the vortex.
- Published
- 1999
- Full Text
- View/download PDF
39. A Study of Stratospheric Aerosols and Their Effect on Inorganic Chlorine Partitioning Using Balloon, In Situ, and Satellite Observations
- Author
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Osterman, G. B, Salawitch, R. J, Sen, B, and Toon, G. C
- Subjects
Environment Pollution - Abstract
Heterogeneous reactions on the surface of aerosols lead to a decrease in the concentration of nitrogen radicals and an increase in the concentration of chlorine and hydrogen radical species. As a consequence, enhanced sulfate aerosol levels in the lower stratosphere resulting from volcanic eruptions lead to lower concentrations of ozone due to more rapid loss by chlorine and hydrogen radicals. This study focuses on continuing the effort to quantify the effect of sulfate aerosols on the partitioning of inorganic chlorine species at midlatitudes. The study begins with an examination of balloon-borne measurements of key chlorine species obtained by the JPL MkIV interferometer for different aerosol loading conditions. A detailed comparison of the response of HCl to variations in aerosol surface area observed by MkIV, ER-2 instruments, HALOE, and ATMOS is carried out by examining HCl vs CH4 correlation diagrams, since CH4 is the only tracer measured on each platform. Finally, the consistency between theory and observed changes in ClO and HCl due to variations in aerosol surface area is examined.
- Published
- 1999
40. The Influence of Airmass Histories on Radical Species during POLARIS
- Author
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Pierson, J. M, Kawa, S. R, Salawitch, R. J, Hanisco, T. F, Lanzendorf, E. J, Perkins, K. K, Gao, R. S, and Cohen, R. C
- Subjects
Environment Pollution - Abstract
The Goddard trajectory chemistry model was used with ER-2 aircraft data to test our current knowledge of radical photochemistry during the POLARIS (Polar Ozone Loss in the Arctic Region In Summer) campaign. The results of the trajectory chemistry model with and without trajectories are used to identify cases where steady state does not accurately describe the measurements. Over the entire mission, using trajectory chemistry reduces the variability in the modeled NO(x) comparisons to data by 25% with respect to the same model simulating steady state. Although the variability is reduced, NO(x)/NO(y) trajectory model results were found to be systematically low relative to the observations by 20-30% as seen in previous studies. Using new rate constants for reactions important in NO(y) partitioning improves the agreement of NO(x)/NO(y) with the observations but a 5-10% bias still exists. OH and HO2 individually are underpredicted by 15% of the standard steady state model and worsen with the new rate constants. Trajectory chemistry model results of OH/HO2 were systematically low by 10-20% but improve using the new rates constants because of the explicit dependence on NO. This suggests that our understanding of NO(x) is accurate to the 20% level and HO(x) chemistry is accurate to the 30% level in the lower stratosphere or better for the POLARIS regime. The behavior of the NO(x) and HO(x) comparisons to data using steady state versus trajectory chemistry and with updated rate coefficients is discussed in ten-ns of known chemical mechanisms and lifetimes.
- Published
- 1999
41. Hydrogen Radicals, Nitrogen Radicals, and the Production of O3 in the Upper Troposphere
- Author
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Wennberg, P. O., Hanisco, T. F., Jaegle, L., Jacob, D. J., Hintsa, E. J., Lanzendorf, E. J., Anderson, J. G., Gao, R.-S., Keim, E. R., Donnelly, S. G., Negro, L. A. Del, Fahey, D. W., McKeen, S. A., Salawitch, R. J., Webster, C. R., May, R. D., Herman, R. L., Proffitt, M. H., Margitan, J. J., Atlas, E. L., Schauffler, S. M., Flocke, F., McElroy, C. T., and Bui, T. P.
- Published
- 1998
42. The Partitioning of NO(sub y) Species in the Summer Arctic Stratosphere
- Author
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Osterman, G. B, Sen, B, Toon, G. C, Salawitch, R. J, Margitan, J. J, Blavier, J. F, Fahey, D. W, and Gao, R. S
- Subjects
Earth Resources And Remote Sensing - Abstract
Volume mixing ratio profiles of the quantitatively significant NOy species NO, NO2, HNO3, HNO4, CINO3 and N2O5 were measured remotely form 8 to 38 km by the JPL MkIV FTIR solar absorption spectrometer during balloon flights from Fairbanks, Alaska on May 8 and July 8, 1997.
- Published
- 1998
43. Measurements of CO in the Upper Troposphere and Lower Stratosphere
- Author
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Herman, R. L, Webster, C. R, May, R. D, Scott, D. C, Hu, H, Moyer, E. J, Yung, Y. L, Wennberg, P. O, Hanisco, T. F, Lanzendorf, E. J, Salawitch, R. J, Margitan, J. J, and Bui, T. P
- Abstract
In situ measurements of CO were made in the upper troposphere and lower stratosphere (7 to 22 km altitude) with the JPL Aircraft Laser Infrared Absorption Spectrometer (ALIAS) on 58 flights of the NASA ER-2 aircraft from October 1995 through September 1997, between 90 degrees North and 3 degrees South latitude.
- Published
- 1998
44. Tropical Entrainment Time Sclaes Inferred from Stratospheric N(sub 2)0 and CH(sub 4) Observations
- Author
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Herman, R. L, Scott, D. C, Webster, C. R, May, R. D, Moyer, E. J, Salawitch, R. J, Yung, Y. L, Toon, G. C, Sen, B, Margitan, J. J, Rosenlof, K. H, Michelsen, H. A, and Elkins, J. W
- Subjects
Geophysics - Abstract
Simultaneous in situ measurements of the long-lived trace gases N(sub 2)O and CH(sub 4) were made with a tunable diode laser spectrometer (ALIAS II) aboard the Observations from the Middle Stratosphere (OMS) balloon platform from New Mexico, Alaska, and Brazil during 1996 and 1997.
- Published
- 1998
45. Measurements and Model Calculations of HNO4: Implications for HO(x)
- Author
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Osterman, G. B, Salawitch, R. J, Sen, B, Toon, G. C, Margitan, J. J, Blavier, J.-F, and Wennberg, P. O
- Subjects
Environment Pollution - Abstract
Establishing a quantitative understanding of the abundance of peroxynitric acid (HNO4) is of interest because the reaction of OH with HNO4 is believed to be a significant sink for HO(x) in the lower stratosphere and upper troposphere. We present concentration profiles of KNO4 obtained by the MkIV Fourier transform infrared spectrometer using the solar occultation technique during two flights, one at 35 N on 25 September 1993 (930925) and the other near 66 N on 7 May 1997 (970507). The observations of HN04 present an apparent dilemma: the calculated profile for HNO4 found using standard kinetics is in relatively good agreement with the mid-latitude observations, but the calculated profile for HNO4 found using the same kinetics overestimates the high-latitude summer observations by nearly a factor of two. Resolution of this dilemma is the focus of our investigation. We show that introduction into our photochemical model of a speculative long-wave (lambda greater than 650 nm) photolytic pathway for HNO4 leads to good agreement between theory and observation of HN04 for both the mid-latitude and high-latitude regions. Implications for the budget of HO(x) are also discussed.
- Published
- 1998
46. ATMOS/ATLAS 3 Infrared Profile Measurements of Clouds in the Tropical and Subtropical Upper Troposphere
- Author
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Rinsland, C. P, Gunson, M. R, Wang, P.-H, Arduini, R. F, Baum, B. A, Minnis, P, Goldman, A, Abrams, M. C, Zander, R, Mahieu, E, Salawitch, R. J, Michelsen, H. A, Irion, F. W, and Newchurch, M. J
- Subjects
Geophysics - Abstract
Vertical profiles of infrared cirrus extinction have been derived from tropical and subtropical upper tropospheric solar occultation spectra. The measurements were recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Sciences (ATLAS) 3 shuttle flight in November 1994. The presence of large numbers of small ice crystals is inferred from the appearance of broad extinction features in the 8-12 micron region. These features were observed near the tropopause and at lower altitudes. Vertical profiles of the ice extinction (/km) in microwindows at 831, 957, and 1204/cm have been retrieved from the spectra and analyzed with a model for randomly oriented spheroidal ice crystals. An area-equivalent spherical radius of 6 microns is estimated from the smallest ice crystals observed in the 8-12 gm region. Direct penetration of clouds into the lower stratosphere is inferred from observations of cloud extinction extending from the upper troposphere to 50 mbar (20 km altitude). Cloud extinction between 3 and 5 microns shows very little wavelength dependence, at least for the cases observed by the ATMOS instrument in the tropics and subtropics during ATLAS 3.
- Published
- 1998
47. Atmos/Atlas 3 Infrared Profile Measurements of Trace Gases in The November 1994 Tropical and Subtropical Upper Troposphere
- Author
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Rinsland, C. P, Gunson, M. R, Wang, P.-H, Arduini, R. F, Baum, B. A, Minnis, P, Goldman, A, Abrams, M. C, Zander, R, Mahieu, E, Salawitch, R. J, Michelsen, H. A, Irion, F. W, and Newchurch, M. J
- Subjects
Geophysics - Abstract
Vertical mixing ratio profiles of four relatively long-lives gases, HCN, C2H2, CO, and C2H6, have been retrieved from 0.01/cm resolution infrared solar occultation spectra recorded between latitudes of 5.3degN and 31.4degN. The observations were obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Science (ATLAS) 3 shuttle flight, 3-12 November 1994. Elevated mixing ratios below the tropopause were measured for these gases during several of the occultations. The positive correlations obtained between the simultaneously measured mixing ratios suggest that the enhancements are likely the result of surface emissions, most likely biomass burning and/or urban industrial activities, followed by common injection via deep convective transport of the gases to the upper troposphere. The elevated levels of HCN may account for at least part of the "missing NO," in the upper troposphere. Comparisons of the observations with values measured during a recent aircraft campaign are presented.
- Published
- 1998
- Full Text
- View/download PDF
48. Ozone Budgets from a Global Chemistry/Transport Model and Comparison to Observations from POLARIS
- Author
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Kawa, S. Randolph, Newman, P. A, Douglass, A. R, Weaver, C. J, Gao, R.-S, Salawitch, R. J, Johnson, D. G, and Jucks, K. W
- Subjects
Environment Pollution - Abstract
The objective of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) field mission was to obtain data to better characterize the summertime seasonal decrease of ozone at mid to high latitudes. The decrease in ozone occurs mainly in the lower stratosphere and is expected to result from in situ chemical destruction. Instrumented balloons and aircraft were used in POLARIS, along with satellites, to measure ozone and chemical species which are involved with stratospheric ozone chemistry. In order to close the seasonal ozone budget, however, ozone transport must also be estimated. Comparison to a global chemistry and transport model (CTM) of the stratosphere indicates how well the summertime ozone loss processes are simulated and thus how well we can predict the ozone response to changing amounts of chemical source gases. Moreover, the model gives insight into the possible relative magnitude of transport contributions to the seasonal ozone decline. Initial comparison to the Goddard CTM, which uses transport winds and temperatures from meteorological data assimilation, shows a high ozone bias in the model and an attenuated summertime ozone loss cycle. Comparison of the model chemical partitioning and ozone catalytic loss rates to those derived from measurements shows fairly close agreement both at ER-2 altitudes (20 km) and higher. This suggests that the model transport is too active in resupplying ozone to the high latitude region, although chemistry failings cannot be completely ruled out. Comparison of ozone and related species will be shown along with a full diagnosis of the model ozone budget and its possible sources of error.
- Published
- 1998
49. Balloon-Borne Measurements of Stratospheric Radicals and their Precursors: Implications for the Production and Loss of Ozone
- Author
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Osterman, G. B, Salawitch, R. J, Sen, B, Toon, G. C, Stachnik, R. A, Pickett, H. M, Margitan, J. J, Blavier, J.-F, and Peterson, D. B
- Subjects
Geophysics - Abstract
Measurements of hydrogen, nitrogen and chlorine radicals from a balloon flight on 25 September 1993 from Ft. Sumner, NM provide an opportunity to quantify photochemical production and loss of stratospheric ozone. Ozone loss rates determined using measured radical concentrations agree fairly well with loss rates calculated using a photochemical model. Catalytic cycles involving OH and HO2 are shown to dominate photochemical loss of ozone for altitudes between 44 and 50 km. Reactions involving NO and NO2 are the dominant sink for ozone between 25 and 38 km. The total ozone loss rate determined from the measurements balances calculated production rates for altitudes between 30 and 40 km. However, loss of ozone exceeds production by -35% between 42 and 50 km. The imbalance between production and loss of ozone above 42 km is larger than the uncertainty of any one of the critical kinetic parameters or species concentrations. No single adjustment to any of these parameters can simultaneously resolve the imbalance and satisfy constraints imposed by measured OH, HO2, NO2 and ClO. Our results are consistent with an additional mechanism for ozone production above 40 km other than photolysis of ground state O2.
- Published
- 1997
- Full Text
- View/download PDF
50. UARS MLS HNO(sub 3) Observations: Implications for Antarctic PSCs
- Author
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Santee, M. L, Tabazadeh, A, Manney, G. L, Salawitch, R. J, Froidevaux, L, Read, W. G, and Waters, J. W
- Abstract
We present Microwave Limb Sounder (MLS) measurements fo gas-phase HNO(sub 3) obtained at the beginning of five southern hemisphere winters.
- Published
- 1997
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