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  • 1
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    Tropospheric chemistry - A global perspective (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Processes that affect the concentration of tropospheric OH are considered, taking into account linkages between the chemistry of OH and the chemistry of H, HO2, and H2O2. A review is presented of observational data of special relevance to OH, notably the distributions of CO, CH4, O3, H2O, HNO3, NO, and NO2. Most of the results presented in connection with the description of the model were obtained by solving time-dependent continuity equations. Rates for photolytic processes were allowed to vary diurnally with insolation. It is found that a well-calibrated and reliable model for OH places important constraints on global budgets for a variety of gases including CH4, H2, and CH3Cl in addition to CO. Accurate measurements of species such as CH3CCl3 can provide valuable checks on global models that must integrate over a variety of atmospheric conditions. However, emission rates for the relevant gases must be adequately quantified.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; Aug. 20
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  • 2
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    Nitrogen oxides in the troposphere - Global and regional budgets (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The cycle of nitrogen oxides in the troposphere is discussed from both global and regional perspectives. Global sources for NO(x) are estimated to be of magnitude 50 (+ or - 25) x 10 to the 12th gm N/yr. Nitrogen oxides are derived from combustion of fossil fuels (40 percent) and biomass burning (25 percent) with the balance from lightning and microbial activity in soils. Estimates for the rate of removal of NOx based on recent atmospheric and precipitation chemistry data are consistent with global source strengths derived here. Industrial and agricultural activities provide approximately two thirds of the global source for NOx. In North America, sources from combustion of fossil fuels exceed natural sources by a factor of 3-13. Wet deposition removes about one third of the combustion source of NOx over North America, while dry deposition removes a similar amount. The balance is exported from the continent. Deposition of nitrate in precipitation over eastern Canada and the western Atlantic is clearly influenced by sources of NOx in the eastern United States.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; 10785-10
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  • 3
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    Distribution functions for energetic oxygen atoms in the earth's lower atmosphere (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Direct photolysis of O3 and quenching of O(1D) by N2 provide abundant sources of fast oxygen atoms for earth's lower atmosphere. The concentration of atoms with energy above 0.7 eV may exceed the concentration of O(1D) for all altitudes below 18 km, and these atoms may play an important role in lower-atmospheric chemistry. Distribution functions for O(3P) are given for the energy interval 0.1-1.3 eV and a range of altitudes from 0 to 62 km.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science; 25; Feb. 197
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  • 4
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    Tropospheric trace gases (1985)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Trace gas concentrations in the atmosphere reflect in part the overall metabolism of the biosphere, and in part the broad range of human activities such as agriculture, production of industrial chemicals, and combustion of fossil fuels and biomass. There is compelling evidence that the composition of the atmosphere is now changing. Observed trends in trace gas levels are reviewed and implications for the chemistry of the atmosphere are discussed. Throughout the discussion, particular emphasis is given to those species which are now increasing in the atmosphere.
    Keywords: GEOPHYSICS
    Type: Atmospheric Ozone 1985. Assessment of our Understanding of the Processes Controlling its Present Distribution and Change, Volume 1; 62 p
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  • 5
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    Simulation of summertime ozone over North America (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The concentrations of O3 and its precursors over North America are simulated for three summer months with a 3D, continental-scale photochemical model using meteorological input from the Goddard Institute for Space Studies (GISS) GCM. The model has 4 x 5 deg grid resolution and represents nonlinear chemistry in urban and industrial plumes with a subgrid nested scheme. Simulated median afternoon O3 concentrations at rural U.S. sites are within 5 ppb of observations in most cases, except in the south central U.S., where concentrations are overpredicted by 15-20 ppb. The model captures successfully the development of regional high-O3 episodes over the northeastern United States on the back side of weak, warm, stagnant anticyclones. Simulated concentrations of CO and nonmethane hydrocarbons are generally in good agreement with observations, concentrations of NO(x) are underpredicted by 10-30 percent, and concentrations of PANs are overpredicted by a factor of 2 to 3. The overprediction of PANs is attributed to flaws in the photochemical mechanism, including excessive production from oxidation of isoprene, and may also reflect an underestimate of PANs deposition. Subgrid nonlinear chemistry as captured by the nested plumes scheme decreases the net O3 production computed in the U.S. boundary layer by 8 percent on average.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; D8; p. 14,797-14,816.
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  • 6
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    Radiative forcing of climate by changes in the vertical distribution of ozone (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Results from a one-dimensional radiative-convective equilibrium model (similar to that of Lacis et al., 1981) of surface-temperature changes induced by changes in the vertical distribution of O3 in the atmosphere are parameterized and applied to measurement data for the northern midlatitudes during the 1970s. The construction of the model is outlined, and the results are presented in tables and graphs and discussed in detail. It is found that decreases in O3 in the lower stratosphere in the 1970s caused atmospheric cooling greater than that due to CO2 (thus possibly obscuring the CO2 greenhouse effect) and surface cooling which outweighed the warming effect of increased O3 in the troposphere. The net surface cooling is shown to be equal to about half of the estimated CO2 warming effect for the period.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 9971-998
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  • 7
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    Oxygen species (1985)
    In:  CASI
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    Publication Date: 2019-08-28
    Description: The spatial distribution of ozone, as predicted by numerical models, is compared with observations. A set of reference ozone profiles was developed against which to compare current numerical calculations. Most of the analyses will focus on ozone between 30 and 70 km altitude.
    Keywords: GEOPHYSICS
    Type: Atmospheric Ozone 1985. Assessment of our Understanding of the Processes Controlling its Present Distribution and Change, Volume 2; 42 p
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  • 8
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    Seasonal variations of troposheric ozone at Natal, Brazil (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: An analysis of ozone measurements from Natal, Brazil (6 deg S, 35 W), with a focus on the seasonal behavior in the troposphere, is presented. The amplitude of seasonal cycle at Natal is much larger than at Panama (9 deg N), the only other tropical site for which similar data are available. Concentrations of ozone in the middle troposphere in the southern spring are unexpectedly high, 60-70 ppb, similar to values found at northern midlatitudes in summer, and larger by 20-30 ppb than values found at Panama and at southern midlatitudes. It is suggested that photochemical production of ozone associated with emissions of CO, hydrocarbons, and NO(x) from biomass burning may contribute significantly to the high values of ozone, but note that stratospheric intrusions could also play a role. The data available at present do not permit a definitive evaluation of the relative importance of these two sources of ozone. The data from Natal, in combination with recent aircraft and surface data, show that tropical ozone exhibits strong spatial and temporal inhomogeneities. The distribution of tropospheric ozone appears to be considerably more complex than the traditional view, which suggested a northern midlatitude maximum and north/-south hemispheric asymmetry. The seasonal cycle in the total column of ozone at Natal appears to mirror the behavior of the tropospheric contribution to the ozone column rather than the stratospheric contribution, and this may account for differences in the annual cycle of the total column at Natal versus other tropical locations.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 7875-788
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  • 9
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    Reductions of Antarctic ozone due to synergistic interactions of chlorine and bromine (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The vertical column density of ozone observed in October over Antarctica has fallen precipitously over the past 10 yr. The concentration at Halley Bay (76 deg S, 27 deg W), expressed conventionally in Dobson units (DU), has dropped from about 300 DU in 1975 to less than 200 DU in 1984. Values in 1985 were even lower, comparable with the lowest values recorded anywhere on earth. It is suggested here that the loss of O3 in Antarctica may be attributed to catalysis of O3 recombination by a scheme in which the rate-limiting step is defined by the reaction of ClO + BrO - Cl + Br + O2. Concentrations of NO2 must be low and heterogeneous reactions involving particles in the polar stratospheric clouds must be an important element of the relevant chemistry. Industrial sources make important contributions to the contemporary budgets of both BrO and ClO and are likely to grow significantly in the future.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 321; 759-762
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  • 10
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    Tropospheric OH in a three-dimensional chemical tracer model - An assessment based on observations of CH3CCl3 (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The paper introduces the representation of tropospheric chemistry allowing for calculation of chemical reaction rates within a chemical tracer model (CTM) simulation with the accuracy comparable to that of a detailed chemical model. The global distribution of tropospheric OH is calculated as a function of time, atmospheric composition, temperature, and solar irradiance. The globally integrated OH concentration weighted by frequency of reaction with CH3CCl3 is evaluated, along with the feasibility of using the observed latitudinal distribution of CH3CCl3 as a test for computed concentrations of OH. Seasonal variations of CH3CCl3 are also considered as a potential test for computed concentrations of OH. It is demonstrated that annual cycles of CH3CCl3 are controlled, or strongly influenced, by dynamical processes at latitudes northward of 25 deg South.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 18441-18
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