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NDACC News and Highlights
2010 NDACC News and Highlights
2010 NDACC News and Highlights
This section highlights significant items of interest within NDACC, with updates at least annually following the NDACC Steering Committee meeting.
Despite its low abundance in the atmosphere, stratospheric bromine contributes up to 25% to the global ozone loss due to its high ozone depletion potential [e.g., World Meteorological Organization (WMO), 2007]. The main sources of bromine in the stratosphere are natural and anthropogenic long-lived and very short-lived brominated organic compounds [e.g., Pfeilsticker et al., 2000; Salawitch et al., 2005]. Long-term observations by in-situ ground-based networks have revealed a decline in total organic bromine from long-lived species by 3 to 5% during the 1998-2004 period [WMO, 2007].
Figure 1: Trend analysis of stratospheric BrO columns over Harestua (60N, 11E; upper plot) and Lauder (45S, 170E; lower plot). More details in Hendrick et al. .
In a recent study by Hendrick et al. , the time evolution of stratospheric bromine monoxide (BrO) has been monitored since 1994 using UV-visible spectrometers operated at two stations of the NDACC: Harestua in Southern Norway (60N, 11E) and Lauder, New Zealand (45S, 170E). Results reveal a significant trend in stratospheric BrO evolving from positive values in the nineties to negative values in most recent years after 2000 (see Figure 1). Accounting for the mean age of air in the stratosphere, the decline in stratospheric bromine since 2002 is found to follow the reported decline of bromine long-lived source gases observed since the second half of 1998. These findings confirm that the impact of the Montreal Protocol restrictions on brominated substances have now reached the stratosphere. Continued high quality NDACC observations of BrO columns and profiles will allow to monitor the future evolution of this important ozone related trace gas. These observations also constitute a key reference for the validation of BrO measurements from recent atmospheric chemistry satellite instruments, such as SCIAMACHY, GOME, GOME-2, OMI, MLS and JEM/SMILES [e.g. Hendrick et al., 2009].
Following a decision endorsed at the 2009 NDACC Steering Committee in Geneva, total column and stratospheric profile BrO measurements performed as part of the NDACC UV-Visible Working Group will be archived in the NDACC data base. In an effort to homogenize data sets and minimize risks of bias and inconsistencies in the retrieved quantities, BrO profiles derived using a commonly agreed Optimal Estimation inversion tool including treatment of the BrO diurnal photochemistry [Schofield et al., 2004; Hendrick et al., 2007] can be centrally produced at BIRA-IASB in agreement with measuring teams. Furthermore, intercomparisons of both BrO slant columns and vertical profile inversion methods are ongoing, e.g. as part of the recent CINDI campaign (see related Hot News on CINDI), and should lead to future consolidation of the NDACC BrO data products.
Hendrick, F., M. Van Roozendael, M. P. Chipperfield, M. Dorf, F. Goutail, X. Yang, C. Fayt, C. Hermans, K. Pfeilsticker, J.-P. Pommereau, J. A. Pyle, N. Theys, and M. De Maziere (2007), Retrieval of stratospheric and tropospheric BrO profiles and columns using ground-based zenith-sky DOAS observations at Harestua, 60N, Atmos. Chem. Phys., 7, 4869-4885.
Hendrick, F., P.V. Johnston, K. Kreher, C. Hermans, M. De Maziere, and M. Van Roozendael (2008), One decade trend analysis of stratospheric BrO over Harestua (60N) and Lauder (44S) reveals a decline, Geophys. Res. Lett., 35, L14801, doi:10.1029/2008GL034154.
Hendrick, F., A. Rozanov, P. V. Johnston, H. Bovensmann, M. De Mazière, C. Fayt, C. Hermans, K. Kreher, W. Lotz, N. Theys, A. Thomas, J. P. Burrows, and M. Van Roozendael (2009), Multi-year comparison of stratospheric BrO vertical profiles retrieved from SCIAMACHY limb and ground-based UV-visible measurements, Atmos. Meas. Tech., 2, 273-285.
Pfeilsticker, K., et al. (2000), Lower stratospheric organic and inorganic bromine budget for the artic winter 1998/99, Geophys. Res. Lett., 27, 3305- 3308.
Salawitch, R. J., D. K. Weisenstein, L. J. Kovalenko, C. E. Sioris, P. O. Wennberg, K. Chance, M. K. W. Ko, and C. McLinden (2005), Sensitivity of ozone to bromine in the lower stratosphere, Geophys. Res. Lett., 32, L05811, doi:10.1029/2004GL021504.
Schofield, R., Kreher, K., Connor, B. J., Johnston, P. V., Thomas, A., Shooter, D., Chipperfield, M. P., Rodgers, C. D., and Mount, G. H.(2004), Retrieved tropospheric and stratospheric BrO columns over Lauder, New Zealand, J. Geophys. Res., 109, D14304, doi:10.1029/2003JD004463.
World Meteorological Organization (WMO) (2007), Scientific assessment of ozone depletion: 2006, Global Ozone Res. Monit. Proj. Rep. 50, Geneva, Switzerland.
In the period from June-July 2009, a large scale intercomparison of UV-Visible spectrometers took place at the Cabauw meteorological observatory, a semi-rural site located in the Netherlands, 30 km South of Utrecht. The main objective of this Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI) was to perform an extensive comparison of NO2 measuring instruments that can be used in support of the validation of tropospheric NO2 column measurements from satellites, with a strong emphasis on the assessment of tropospheric NO2 column and profile measurements using the MAXDOAS technique. The campaign included a formal semi-blind exercise following standards from the Network for the Detection of Atmospheric Composition Change (NDACC), and was followed by a number of additional activities. In total measurements from 32 NO2 instruments, most of them of DOAS-type but also data from a NO2 Lidar, in-situ sensors and a newly-developed NO2 sonde, were collected and intercompared. A number of additional parameters were also measured, including aerosol and other trace gases like HCHO, CHOCHO, BrO and ozone. Moreover special measurements were performed to study horizontal gradients in atmospheric composition and their impact on remote-sensing observations. After the campaign various working groups were set up to analyse results with the aim to progress towards improved and standardized retrieval algorithms. The campaign should result in consolidated trace gas and aerosol data products from both remote-sensing and in-situ techniques, thereby contributing to fulfill the needs for improved vertically-resolved monitoring of the air quality.
More information on the CINDI web-site: http://www.knmi.nl/samenw/cindi/index.php
A highly variable interference has long been considered the dominant feature of water vapor for practitioners who retrieve atmospheric total column amounts and profiles from infrared solar absorption spectra. Due to the importance of water as a greenhouse gas and its possible long-term trend resulting from changes in the atmosphere and subsequent feedback effects there is renewed effort in extracting water vapor quantities from archived solar spectra, which for some sites stretch back to the 1970's. Several groups in the NDACC InfraRed Working Group (IRWG) community have recently published papers aimed at determining the maximum information content from existing spectral measurements. Two primary tasks are to understand the effect of variability and to determine the vertical extent of the measurements.
Recently Sussman et al.  compared coincident measurements at the European continental NDACC sites at Zugspitze and the two instrument data sets at Jungfraujoch to determine coincidence effects on consistent measurements of integrated water vapor (IWV). Figure 1 shows the standard deviations between IWV measurements from two FTS systems taken at intervals of minutes to several hours. This dramatically illustrates that large variability occurs on sub-diurnal timescales. It thus constrains the time lag for useful coincident measurement intercomparisons to below 1 hour.
Figure 1. (After Sussmann 2009) Standard deviation of IWV in mm H2O vs observation coincidence interval for two co-located FTIR instruments. The point numbers are the number of coincident observations.
The IWV value is dominated by water in the lowest part of the atmosphere. However, quantifying the mixing ratio nearer the tropopause is of importance for understanding atmospheric trends and climate change. The same retrieval technique that can produce the IWV content can be used to derive partial columns at different vertical intervals. These are characterized by the retrieval averaging kernels that are shown in Figure 2 for the NDACC site at Tenerife where the sensitivity falls off rapidly above 8km to 50% at 13km. The interrelation of the humidity and temperature at the tropopause is a controlling feature of the humidity entering the stratosphere. These issues are an important active area of study and using these techniques on the global IRWG spectral archive will reveal long-term changes in some of these factors.
Figure 2, (After Schneider 2010) Typical averaging kernels for ground-based FTIR remote sensing of watwer vapor. Kernels for 3, 5 and 8km are highlighted in red, green and blue respectively and the sensitivity in black.
Schneider, M., P. M. Romero, F. Hase, T. Blumenstock, E. Cuevas, and R. Ramos Continuous quality assessment of atmospheric water vapour measurement techniques: FTIR, Cimel, MFRSR, GPS and Vaisala RS92, Atmos. Meas. Tech., 3, 323 - 338, 2010.
Sussmann, R., T. Borsdorff, M. Rettinger, C. Camy-Peyret, P. Demoulin, P. Duchatelet, E. Mahieu, and C. Servais Technical Note: Harmonized retrieval of column-integrated atmospheric water vapor from the FTIR network - first examples for long-term records and station trends, Atmos. Chem. Phys., 9, 8987 - 8999, 2009.
High spectral-resolution infrared solar transmission spectra contain information about the vertical distribution of the absorbing species in the terrestrial atmosphere due to the pressure broadening of the absorption lines. This feature is being exploited in the Infrared Working Group to retrieve vertical profile information of several atmospheric trace gases, such as O3, CO, N2O, CH4, HCl, HF, HNO3, C2H6 and HCN, in addition to the total column abundances. For more than 5 years, efforts have been made to define vertical profile retrievals that are consistent across the network and these retrieval standards are currently in a mature form. This implies that the IRWG will revise certain time series of column abundances in order to now deliver time series of vertical profile data to the NDACC DHF. The IRWG has adopted the HDF data format as it is well suited for storage of profile data and the associated averaging kernels and auxiliary data that characterize the retrieval results and has become the standard for distribution and archiving of remotely sensed data. In establishing its HDF formatting guideline the IRWG worked in close collaboration with AVDC (AURA Validation Data Center), EVDC (Envisat Validation Data Center) and the NDACC Data Host Facility. The archiving of profile data in HDF format began as of autumn 2009.
NDACC established the designation of "Cooperating Network" to formalize the relationship with regional, hemispheric, or global networks of instruments that operate independently of NDACC, but where strong measurement and scientific collaboration is mutually beneficial. More information on the "Cooperating Network" Protocol is found in the "Protocols" area of the NDACC web pages.
In the Fall of 2009, five Networks signed memoranda of understanding to complete the Cooperating Network designation. These networks are:
The Measurements and Analyses Directory contains a complete listing of all NDACC Affiliated Measurements, both long-term and campaign, as well as a listing of the Cooperating Networks, and the Theory and Satellite Working Group Members. This document has been completely revised and reflects all newly accepted measurements including those of the newly accepted Spectral UV Instruments from Biospherical Instruments, the re-established measurements at Eureka, the new lidar water vapor measurements, and more. The Directory also reflects the reorganization of the NDACC eliminating the Primary/Complementary Station status. The stations are now grouped only as long- or short-term/campaign. Measurement activities are listed by station location, giving full activity description in this section. Additionally for each instrument type there is given a list of stations supporting that measurement type. The new Measurements and Analyses Directory is available in the NDACC web pages.
The NDACC Steering Committee has developed a graphic to depict the measurement capabilities of the network. The chart provides a summary of the species and parameters whose measurements are archived in the DHF, the instrumental techniques employed for the measurements, and an indication of the approximate vertical resolution of the measurements. This chart, available here, will also shortly be available in the instrument area of the NDACC web pages.