Atmospheric Sciences I
Presiding: D F Rault, NASA Langley Research Center; K Chance, Harvard-Smithsonian Center for Astrophysics
A11A-01 08:30h
Validation analysis for SAGE III limb scattering Ozone products
The Stratospheric Aerosol and Gas Experiment (SAGE III) instrument is being used to investigate the potential of limb scattering methods for atmospheric gas/aerosol vertical profile retrieval. The information contained in the Earth limb scattered sunlight measured by SAGE III has been shown to be sufficient to retrieve Ozone density from 10 km (or cloud top) to 50-55 km using UV and visible wavelengths [Rault, JGR 2005], as well as NO2 density from 15 to 40 km and stratospheric aerosol extinction profiles. Initial results have shown that the retrieved profiles compare favorably with correlative measurements, such as Ozone sondes and other satellite instruments (namely, SAGE II, HALOE, SAGE III in occultation, POAM, OSIRIS). The present paper summarizes the results of an extensive validation study for SAGE III limb scatter Ozone products. The validation analysis considers two data sets, namely (1) measurements made while overpassing a series of ground stations belonging to the SHADOZ network during Summer 2004 and Fall 2004, and (2) measurements made during the Summer 2004 INTEX campaign over North America, North Atlantic and Northern Europe.
A11A-02 08:45h
Estimating Emissions of Ozone Precursors in Europe Through Inverse Modeling of Ozone and Nitrogen Dioxide Observations
We report on the first inverse modeling study for estimating emissions of ozone precursors in Europe. A Kalman smoother was applied in combination with the atmospheric chemistry transport model, EUROS, and rural observations of O3 and NO2 to estimate emissions of NOx and VOCs for several groups of countries. The study focused on the middle-west of Europe, i.e. around the Netherlands, Germany, the UK, and France, simply because this region shows the most observations of O3 and NO2 at rural sites. Emissions of the ozone precursors are assessed by European countries and reported to EMEP. The NOx emissions derived with inverse modeling are about 30-40% below the EMEP emissions for the Belgium-Netherlands-Luxembourg and Germany-Denmark regions, and about 60% for the UK-Ireland region. The NOx emissions in France are slightly higher than the EMEP emissions, but this difference is almost within the uncertainty range. The VOC emissions derived with inverse modeling agree with those from EMEP within the estimated uncertainties. The NOx and VOC emissions reported by the countries to EMEP show a downward trend for the 1999-2002 period. This downward trend cannot be confirmed by the derived inverse modeling emissions. Extensive simulations with the Kalman smoother show that the uncertainties in derived emissions are dominated by the choice of observations used in the assimilation (O3, NO2, or both) and by the choice of noise parameters (NOx, VOC, or NOx + VOC emissions). The overall uncertainty in NOx emissions, estimated as the sum of different components, is estimated at 12-23% for NOx emissions and at 23-56% for VOC emissions for the Belgium-Netherlands-Luxembourg, Germany-Denmark, France, and UK-Ireland regions. These uncertainties do not take into account the uncertainties associated with possible systematic errors in the physical and chemical parameterizations in the EUROS model. The simulations with different combinations of noise and observations showed that inverse modeling with EUROS yields consistent NOx emissions if using NO2, or NO2 and O3, observations simultaneously and consistent VOC emissions if using NOx and VOC emissions simultaneously as noise parameters. Application of noise in VOC emissions and NOx emissions simultaneously affects the derived NOx and VOC emissions significantly when compared to the application of noise to these emissions individually.
A11A-03 09:00h
Ozone Surface Flux Measurements Over the Antarctic Snow Pack
Boundary layer ozone depletion events have previously been observed in the Antarctic Spring, however the exact mechanism for the destruction is not fully understood. The snow surface and blowing snow is thought to play a role in ozone loss but it is unclear if ozone loss is a physical process on the large surface area provided by the snow or through a chemical reaction with species released from the snow. Micrometeorological measurements of surface ozone fluxes were carried out on the Ross Ice Shelf in the austral spring of 2004. These measurements were made using a newly developed fast time-response (> 1 Hz) closed-path optical absorption ozone analyzer. This first deployment of the instrument demonstrated significant improvements in temporal resolution of ozone data as well as high reliability in very harsh conditions. The instrument was configured to measure fluxes using the eddy correlation method in conjunction with a sonic anemometer, and using a gradient flux method with multiple inlets on a flux tower. Simultaneous measurements were also made of meteorological conditions and trace concentrations of nitrogen oxides. The instrumentation ran autonomously and regularly for ten weeks, gathering a comprehensive data set of surface ozone conditions. Observations of ozone concentrations over the depth of the boundary layer were also made using a tethered ozone sonde. Initial results show depletion of ozone in the bottom 1 to 50 meters of the planetary boundary layer, suggesting that the snow surface may play an important role in Antarctic boundary layer ozone depletion events.
A11A-04 09:15h
Ozone Observations by the Gas and Aerosol Measurement Sensor During SOLVE II
The Gas and Aerosol Measurement Sensor (GAMS) was deployed aboard the NASA DC-8 aircraft during the second SAGE III Ozone Loss and Validation Experiment (SOLVE II) based in Kiruna, Sweden during January-February 2003. GAMS acquired line-of-sight (LOS) direct solar irradiance spectra during the sunlit portions of eleven science flights of the DC-8 between January 11 and February 6, 2003. Differential LOS ozone number densities are retrieved from the GAMS spectra using a multiple linear regression spectral fitting technique. GAMS ozone measurements are compared with coincident ozone measurements from two other solar instruments aboard the DC-8 platform to demonstrate the robustness and stability of the GAMS ozone retrievals. The GAMS ozone measurements are then utilized to experimentally assess the quality of the ozone molecular absorption cross-sections tabulated for the ozone Wulf bands that extend from near 730 to 1030 nm. Accurate knowledge of the Wulf band ozone cross sections is critical to the success of the SAGE III temperature/pressure, water vapor, and aerosol retrievals. Results from this study suggest the ozone cross section compilation of Shettle and Anderson currently used operationally in SAGE III data processing may be in error by as much as 10-20% in the Wulf bands and their lack of reported temperature dependence is a significant deficiency. An ozone cross section database compiled for the SCIAMACHY satellite mission appears to be of better quality in the Wulf bands, but still may have errors in shape as large as 5-10%. Additional laboratory measurements of the Wulf band cross sections should be pursued to further reduce their uncertainty and better quantify their temperature dependence.
A11A-05 09:30h
Ozone Depletion Potentials of HCFC-123 and HCFC-124
The Montreal Protocol has phased out most chlorinated and brominated compounds because of their great efficiency in depleting ozone in the stratosphere. Compounds such as CHCl2CF3 (HCFC-123) and CHClFCF3 (HCFC-124) are being used in commercial refrigeration units and have much shorter atmospheric lifetimes than the chlorofluorocarbons they replace. Despite their small resulting Ozone Depletion Potentials (ODPs), these compounds are still currently expected to be eliminated under the existing Protocol, but there remain questions about finding suitable replacements that would not have other environmental effects. The HCFC-123 and HCFC-124 model-calculated atmospheric lifetimes of 1.3 years and 5.8 years are much shorter compared to the 45 years of CCl3F (CFC-11). In this study, we have reevaluated these compounds with an updated version of the UIUC two-dimensional chemical transport model and with the MOZART (version 3) three-dimensional chemical-transport model. The new version of the two-dimensional model gives ODPs of 0.012 and 0.0125 for HCFC-123 and HCFC-124, respectively. The ODP for HCFC-123 agrees well with previously reported values while the ODP for HCFC-124 is much smaller than earlier estimates. These analyses along with those from the three-dimensional modeling studies will be discussed in the presentation.
A11A-06 09:45h
OMI Measurements of BrO, OClO, and HCHO
We report progress in determining abundances of the trace gases BrO, OClO, and HCHO from the EOS-Aura Ozone Monitoring Instrument. Updates and improvements in the data analysis algorithm are described and examples of measurements given. OMI BrO includes releases from the shelf ice in 2004 Antarctic spring. HCHO includes production from biogenic sources, biomass burning, and possibly from agriculture and urban pollution. We will examine Asian HCHO production changes before and after the December 26, 2004 tsunami. OClO from Arctic spring 2005 will be presented if measurable enhancements have occurred in time to analyze and present at the meeting.