Determination of the atmospheric concentrations and lifetime of trichloroethane (CH sub(3)CCl sub(3)) is very important in the context of global change. This halocarbon is involved in depletion of ...ozone, and the hydroxyl radical (OH) concentrations determined from its lifetime provide estimates of the lifetimes of most other hydrogen-containing gases involved in the ozone layer and climate. Global measurements of trichloroethane indicate rising concentrations before and declining concentrations after late 1991. The lifetime of CH sub(3)CCl sub(3) in the total atmosphere is 4.8 plus or minus 0.3 years, which is substantially lower than previously estimated. The deduced hydroxyl radical concentration, which measures the atmosphere's oxidizing capability, shows little changes from 1978 to 1994.
United States. National Aeronautics and Space Administration (Grant NAG5-12669)
Great Britain. Department for Environment, Food and Rural Affairs (grants EPG 1/1/159)
Great Britain. Department for ...Environment, Food and Rural Affairs (grants GA01081)
United States. National Aeronautics and Space Administration (Grant NNX07AE89G)
Carbon tetrachloride (CCl4) has substantial stratospheric ozone depletion potential and its consumption is controlled under the Montreal Protocol and its amendments. We implement a Kalman filter using atmospheric CCl4 measurements and a 3-dimensional chemical transport model to estimate the interannual regional industrial emissions and seasonal global oceanic uptake of CCl4 for the period of 1996–2004. The Model of Atmospheric Transport and Chemistry (MATCH), driven by offline National Center for Environmental Prediction (NCEP) reanalysis meteorological fields, is used to simulate CCl4 mole fractions and calculate their sensitivities to regional sources and sinks using a finite difference approach. High frequency observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Earth System Research Laboratory (ESRL) of the National Oceanic and Atmospheric Administration (NOAA) and low frequency flask observations are together used to constrain the source and sink magnitudes, estimated as factors that multiply the a priori fluxes. Although industry data imply that the global industrial emissions were substantially declining with large interannual variations, the optimized results show only small interannual variations and a small decreasing trend. The global surface CCl4 mole fractions were declining in this period because the CCl4 oceanic and stratospheric sinks exceeded the industrial emissions. Compared to the a priori values, the inversion results indicate substantial increases in industrial emissions originating from the South Asian/Indian and Southeast Asian regions, and significant decreases in emissions from the European and North American regions.
Great Britain. Department for Environment, Food and Rural Affairs (grant CPEG 24)
United States. National Aeronautics and Space Administration (Grant NNX07AF09G)
United States. National Aeronautics and Space Administration (Grant NAG5-12099)
National Science Foundation (U.S.) (grant ATM-0120468)
United States. National Aeronautics and Space Administration (Grant NNX07AE87G)
A numerical procedure is presented for computing the transfer impedance between two antennas located above a two-dimensional ground surface of known contour. The antennas are either both horizontally ...or both vertically polarized, and may have arbitrary radiation patterns in the vertical plane. The antennas are assumed to be high enough above the ground so that surface wave coupling is negligible but close enough so that a significant portion of the received power arrives via ground scattering. For purposes of computation, the ground is divided into a series of connected (infinite) planar strips of identical projected width. The net scattered field is computed using Green's theorem applied to each strip individually but neglecting edge effects and multiple scattering. The practical utility of this technique has been tested in a limited way by measuring the variation in coupling between two identical horizontally polarized horn-aperture antennas over a single ground contour. Provided the baseline profile is surveyed carefully at the time the coupling measurements are made, the numerical predictions are seen to be in reasonable agreement with the test data.
Trace gas simulations using the 3-D Regional chEmical trAnsport Model (REAM) for February to May 2000 over North America are applied to analyze surface, aircraft, and satellite measurements to ...understand the springtime transitions of key trace gas concentrations and export. The global GEOS-CHEM model is used to provide chemical initial and boundary conditions and the global model results are compared with REAM. Surface observations from AIRNOW (EPA) and SEARCH networks, aircraft observations from the TOPSE and MOZAIC experiments, ozonesondes, and remote sensing measurements from GOME, MOPITT, TOMS and SAGE are analyzed. Generally, the model results are in good agreement with the observations in the troposphere. Above 350 hPa, the mdoel has a low bias in simulated ozone concentrations due to the specified upper boundary concentrations. We highlight a few results here. We find that the simulated boundary layer structure is a key process that differentiates REAM simulations from GEOS-CHEM. As a result, the activation of photochemistry in the boundary layer and the resulting increase of ozone concentrations in spring are much faster in GEOS-CHEM than REAM or in surface observations. It also contributes to substantial difference of monthly mean NO2 columns between the two models. However, when averaged over the 4 months period, the model-to-model difference as well as month-to-month variability is averaged out. The agreement among GOME and two model simulated NO2 columns are well within the uncertainties of GOME measurements, rendering the a posteriori NOX emissions essentially the same as the a priori. Lastly, the lightning NOX production in REAM is much larger than GEOS-CHEM, resulting in better simulations of NO2 columns over the western North Atlantic than GEOS-CHEM. Consequently, REAM shows a significantly larger increasing trend of ozone column over the southern part of western North Atlantic than GEOS-CHEM.
The Recovery of Earth's Ozone Layer Yang, E; Cunnold, D M; Newchurch, M J ...
Eos (Washington, D.C.),
12/2006, Letnik:
87, Številka:
52
Magazine Article
The Montreal Protocol and its amendments have severely limited industrial production of chlorofluorocarbons (CFCs) and other ozone depleting halogenated compounds, resulting in recent slight declines ...in stratospheric halogen loading. All else being equal, this change is expected to lead to the first stage of ozone recovery, marked by a statistically significant slowing of the prior, long term downward trend. Indeed, ozone levels have stopped declining at mid-latitudes, in the Antarctic ozone hole, and in the region of the Southern Hemisphere that surrounds the ozone hole. Attribution of ozone changes is complicated, however, due to influences on ozone of factors such as atmospheric transport, volcanic aerosol loading, cyclical variations in solar ultraviolet irradiance, and chemical factors unrelated to halogens (e.g., water and methane). We will describe changes in ozone throughout Earth's atmosphere, from 1979 to 2005, as measured by a comprehensive set of ground-based, balloon, and satellite instruments. We will discuss the statistical significance of these recent improvements and show that for some, but not all regions of Earth's atmosphere, these improvements can be attributed to declining levels of stratospheric halogens that have resulted from the Montreal Protocol.
The scales of temporal and spatial variations in stratospheric minor species concentrations and dynamical quantities are briefly reviewed. Despite the fact that the stratosphere is often considered ...to be a very quiescent region of the atmosphere, it exhibits transient and generally unpredictable episodes of intense activity. The resultant necessity for some degree of coordination between different observers in their choice of locations and times for measurements of minor constituents is emphasized. We provide the specific suggestion of one or more short "International Stratospheric Periods" whose duration would depend upon the time of year. During these short periods, as many observers as possible would perform an integrated series of observations designed to optimize the usefulness of their data to atmospheric scientists.
PDF
