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Stratospheric Processes And their Role in Climate
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| Home | Initiatives | Organisation | Publications | Meetings | Acronyms and Abbreviations | Useful Links |
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Stratospheric Processes And their Role in Climate
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| Home | Initiatives | Organisation | Publications | Meetings | Acronyms and Abbreviations | Useful Links |
Michael H. Proffitt, World Meteorological Organization, Atmospheric Research and Environment Programme, Environment Division, Geneva, Switzerland (proffitt@wmo.ch)
Monitoring of trace atmospheric constituents was originally driven by scientific curiosity.
It was not long, however, before questions were raised as to what the consequences would be for humanity should the observed increases in certain
trace chemicals continue unabated. The development of major international activities concerned with protection of the environment started in earnest
during 1968 when the United Nations was called upon to organise a world conference on internationally significant problems related to the human
environment. The conference took place in Stockholm in 1972 and successfully drew world-wide attention to environmental problems, including
changes in the atmosphere due to rapid industrialisation.
During the 1970s three important atmospheric issues were addressed: (a) the threat of CFC’s to the ozone layer, (b) acidification of
lakes and forests in large parts of North America and Europe, caused principally by the conversion of sulphur dioxide into sulphuric acid by
precipitation processes in the atmosphere and, (c) potential global warming caused by the build-up of greenhouse gases in the atmosphere.
Each of these issues is now the subject of international treaties or conventions. The initial development of these agreements and the subsequent
assessments of the mitigation measures they contain, rely heavily on the information derived from WMO's atmospheric composition monitoring
programme.
The WMO formally embarked on a programme of atmospheric chemistry and meteorological aspects of air pollution during the 1950s. This included
assuming responsibility for standard procedures for uniform ozone observations and establishing the Global Ozone Observing System (GO3OS)
during the 1957 International Geophysical Year. In the late 1960s, the Background Air Pollution Monitoring Network was established which was
subsequently consolidated with the Global Ozone Observing System into the current WMO Global Atmosphere Watch (GAW) in 1989. The GAW
monitoring programme includes a co-ordinated global network of observing stations along with supporting facilities. GAW provides data for
scientific assessments and for early warnings of changes in the chemical composition and related physical characteristics of the atmosphere
that may have adverse affects upon our environment. Monitoring priorities have been given to greenhouse gases for possible climate change,
ozone and ultraviolet radiation for both climate and biological concerns, and certain reactive gases and the chemistry of precipitation for a
multitude of roles in pollution chemistry.
The GAW programme was briefly described in SPARC Newsletter N° 7 (1996) with emphasis
on the very successful GO3OS. The GAW programme has matured considerably since then, and presently consists of many co-ordinated components
that have been designed to provide accessible, high quality atmospheric data to the scientific community. These components include: (a) measurement
stations, (b) calibration and data quality centres, (c) data centres and (d) external scientific groups for programme guidance.
Figure 1 shows
the principal components making up the GAW programme. Support for these components is provided, in large part, by individual WMO Member
countries that directly participate in the GAW programme, augmented by some outside international funding, and the WMO
Secretariat’s internal budget.
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Monitoring Components of GAW
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Figure 1. Principal components making up the GAW programme.
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(Please contact the SPARC Office, for a better resolution of the image)
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A network of measurement stations is the backbone of the GAW programme. This network consists of GAW Global and Regional measurement stations with additional measurements from Contributing and Associate stations. The present network of 22 GAW Global stations is shown in Figure 2. Global stations are usually situated in remote locations, representative of large geographic areas, have very low (background) levels of pollutants, and continuously measure a broad range of atmospheric parameters over decades. It is important to note that Global station sites must be entirely free of the effects of local and regional pollution sources for substantial periods throughout the year. Data are typically applied to global issues such as climate change and stratospheric ozone depletion.
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Figure 2. The present network of the 22 GAW Global stations.
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(Please contact the SPARC Office, for a better resolution of the image)
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GAW Regional stations are usually representative of smaller geographic regions. Regional station sites are often chosen so they are not affected
by nearby sources of pollution such as vehicles, industrial combustion or agricultural activities. Measured parameters vary considerably at Regional
stations, and depend upon the regional needs. Some Regional stations measure a broad range of parameters, while others measure only a single
measurement type. Not all atmospheric parameters can or even should be measured at each GAW Station. For example, a site with excessive local
pollution may still be suitable for column ozone and solar radiation but not for background measurements of greenhouse gases. Data from Regional
stations are typically applied to more local or regional issues such as acid deposition, transport of trace gases and aerosols, regional background
pollution levels, and local UV or ozone conditions. Both Global and Regional stations are operated by their host countries, either by their National
Meteorological Services or by other national scientific organisations. More than 65 countries actively host GAW stations.
In addition, there are stations that have not been formally designated as either Global or Regional GAW stations, but nevertheless make very
valuable contributions to the GAW programme through submitting data to the GAW World Data Centres (WDCs). Such stations are classified as
either Contributing stations or Associate stations. Contributing stations belong to other organisations such as the Network for Detection of
Stratospheric Change (NDSC), the European Monitoring and Evaluation Programme (EMEP), or the Baseline Surface Radiation Network (BSRN).
Through mutual agreements, these contributing organisations are under the GAW umbrella of stations. Some of these Contributing stations have
dual affiliations within GAW, having also an established Global or Regional GAW station status. And finally, there are the Associate stations that
submit data to the WDCs without any formal GAW affiliation. These include many single measurement stations as well as air and ship
platforms.
The calibration and the data quality centres are either regional or global in responsibility. These centres perform the vital function of helping to
ensure that the data submitted to the GAW World Data Centres is of sufficient quality to meet the needs of the scientific research community. Their
activities include (a) careful calibration of instruments through station visits, (b) instrument intercomparisons and calibration campaigns,
(c) laboratory measurement intercomparisons of circulated standard gases or reference samples, and (d) systematic and frequent calibration
checks of the world standards. Whenever possible, measurement calibrations are traceable to the GAW world calibration standards.
Although these direct calibration activities are required to maintain the required comparability of measurements globally, the GAW data quality
programme includes other activities. For example, during station visits, GAW Calibration Centres provide on-site training and expert advice
to help station personnel maintain the required data quality. Workshops are also held during intercomparisons and calibration campaigns,
while instrument repairs or upgrades are often performed on the spot by technical experts. Further help is provided to the less experienced
personnel at new stations by personnel from well established and technically advanced stations. In addition, there are GAW training centres
sponsoring frequent training sessions for station personnel, particularly those located in developing countries.
The GAW World Data Centres (WDCs) are operated and maintained by their individual host institutions. They collect, document and archive
atmospheric measurements and the associated metadata from measurement stations world-wide and make these data freely available to the scientific
community. In some cases, WDCs also provide additional products including data analyses, maps of data distributions, and data summaries.
Presently, there are six GAW WDCs each responsible for archiving one or more GAW measurement parameters or measurement types.
Measurement types presently archived include ozone (surface, total column, vertical column), greenhouse and carbon cycle gases, oxides of
nitrogen, chemistry of precipitation, chemical and physical properties of aerosols, solar radiation including ultraviolet, and station meteorological
parameters. The data residing in the WDCs are always subject to change, for example, from new calibrations. For this reason, data providers
at individual stations should always be contacted directly for detailed information on such changes. In order that data providers be given
appropriate recognition, scientists accessing the data are required to accept the following conditions: “For scientific purposes, access
to these data is unlimited and provided without charge. By their use you accept that an offer of co-authorship will be made through personal
contact with the data providers or owners whenever substantial use is made of their data. In all cases, an acknowledgement must be made to
the data providers or owners and the data centre when these data are used within a publication.”
The World Ozone and Ultraviolet Radiation Data Centre is operated by the Experimental Studies Division of the Meteorological Service of Canada
(MSC), until recently known as the Atmospheric Environment Service, Environment Canada. The Data Centre began as the World Ozone Data Centre
(WODC) in 1960 and in June 1992, the MSC agreed to a request from the WMO to add ultraviolet radiation data to the WODC. The Data Centre has
since been renamed the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) with the two component parts: the WODC and the World Ultraviolet
Radiation Data Centre (WUDC).
The WODC operates a scientific archive and database providing a variety of ozone data sets to the international scientific community. Some data
records date back more than 40 years. Data sets include total column ozone and vertical profile data from ozonesonde flights, lidar measurements
and the Umkehr technique. Archived data are available by conventional FTP access or by a direct link from the WOUDC Data Web page. At present,
access to the archive by conventional FTP requires a username and password, which is available upon request. Value added data products
include total ozone time series graphs and near real-time ozone maps.
The WUDC like its ozone counterpart, is a scientific archive and database of high resolution spectral, multi-band and broad-band UV data.
The database started receiving data in early 1993.
At present, there are over 400 registered stations represented in the WOUDC archive. Metadata information such as station lists with locations,
are available from the WOUDC Web site: http://www.msc.ec.gc.ca/woudc.
The World Radiation Data Centre (WRDC) is located in St. Petersburg at the Main Geophysical Observatory of the Russian Federal Service for
Hydrometeorology and Environmental Monitoring. The WRDC was established in 1964, and since that time it centrally collects, archives and publishes
radiometric data for the world, to ensure the availability of these data for research purposes by the international scientific community. It issues
a periodic bulletin entitled "Solar Radiation and Radiation Balance Data. The World Network."
The WRDC processes solar radiation data currently submitted from more than 500 stations located in 56 countries and operates an archive with
more than 1200 stations listed in its catalogue. The WRDC is the central depository of the measured components such as: global, diffuse and direct
solar radiation, downward atmospheric radiation, net total and terrestrial surface radiation (upward), spectral radiation components
(instantaneous fluxes), and sunshine duration, on hourly, daily or monthly basis.
At the present time, recent and current data can be viewed by accessing the WRDC web site. It also contains a list of all stations that have
submitted data. As new measurement data are received from National Meteorological Services and other institutions in paper form, on magnetic
media or electronically, the WRDC performs a supplementary quality control and requests stations to confirm the data for total quality
assurance. The data from GAW sites is represented in a specified directory as tables and as figures including graphs showing relationships
between measured and estimated parameters: http://wrdc.mgo.rssi.ru.
The responsibility for the World Data Centre for Precipitation Chemistry (WDCPC) was originally given to the US Environmental Protection
Agency (EPA) which operated the programme until 1994. The responsibility was subsequently transferred to the Atmospheric Sciences Research
Center (ASRC) of the State University of New York at Albany, and is supported by US government agencies.
The Data Centre is responsible for documenting, archiving and making available data on the chemical components of precipitation that has
been collected at hundreds of stations around the world. The precise chemical composition of each sample is determined by collaborating
laboratories working within strict guidelines and standards developed under GAW.
The samples are analysed for many chemical constituents and its acidity or alkalinity. Specifically, the chemical constituents of interest are:
sodium, potassium, magnesium, calcium, fluoride, chloride, bromide, ammonium, nitrate, sulphate, sulphur, phosphate tribasic, mercury,
aluminium, cadmium, copper, iron, manganese, nickel, lead, zinc, phosphorus, iodine, nitrite, and sulphite
(http://marble.asrc.cestm.albany.edu/qasac/gaw_maps.html).
The World Data Centre for Greenhouse Gases (WDCGG) was established at the Japan Meteorological Agency
(JMA) in October 1990 and collects and distributes data on the mixing ratios of greenhouse (CO2, CH4, CFCs,
N2O, etc.) and related reactive (CO, NOx, SO2, VOC, etc.) gases in the atmosphere and the ocean.
Simultaneously measured meteorological parameters are also recorded at WDCGG.
Data contributors submit their data on diskettes, coding sheet, or via FTP according to a prescribed format. As of February 2000, 182
stations in 42 countries submitted observational data for 13 species of greenhouse and related gases to the WDCGG. The WDCGG periodically
publishes the "WMO WDCGG Data Report", "WMO WDCGG CD-ROM", "WMO WDCGG Data
Catalogue" and "WMO WDCGG Data Summary". The "Data Report" contains monthly and annual means and
the "CD-ROM" also contains hourly and daily means. Information on contact persons, methods of measurement and calibration at
the observation stations is also made available, and all data can be accessed by FTP file transfers. The "Data Catalogue" provides
an index of existing data along with procedures for data access. It also includes information on site environment, measurement procedures,
and calibration techniques. The "Data Summary" includes averaged results from the past and present conditions on local, regional,
and global scales (http://gaw.kishou.go.jp/wdcgg.html)
The World Data Centre for Aerosols (WDCA) is operated by the European Union's Joint Research Centre, Ispra, Italy, and was set up to archive
aerosol related observations made under GAW. A wide variety of aerosol parameters have been recommended by the GAW Scientific Advisory Group
for Aerosols as suitable for measurement and archiving at GAW Regional and Global stations.
Recommended aerosol parameters for frequent measurement at Regional stations:
Clearly, few stations can make all of these measurements, while many stations are making only one or two of these observations. At the moment, WDCA is concentrating on building up the archives of commonly available parameters, including chemical composition, aerosol optical properties, and CN concentrations (http://www.ei.jrc.it/wdca/).
The World Data Centre for Surface Ozone (WDCSO) was formally established in June 1997 and is the newest of the six WDCs. The Data Centre has been operational since August 1998 as an integral part of the Norwegian Institute for Air Research's (NILU) Atmospheric Database for Interactive Retrieval (NADIR). WDCSO provides a quality archive for surface ozone measurements originating from the WMO-GAW umbrella of monitoring stations and from other measurement programmes and campaigns (http://www.nilu.no/projects/nadir/wdcso3/wdcso3.html).
The WMO Commission for Atmospheric Sciences (CAS) is the lead WMO technical commission for research activities (including those of GAW)
in the atmospheric sciences and related fields. The Executive Council Panel of Experts/CAS Working Group on Environmental Pollution and
Atmospheric Chemistry (EC Panel) has been designated as the overall steering body for GAW. The EC Panel is composed of internationally known
experts that are representative of a broad range of interests in atmospheric chemistry relevant to the GAW programme.
The EC Panel has established Scientific Advisory Groups (SAGs) to organise and co-ordinate GAW activities for five parameter types: ozone,
greenhouse gases, UV, precipitation chemistry, and aerosols. Each SAG is responsible for establishing and overseeing the implementation of data
quality criteria and standard operating procedures for its assigned parameter type. In addition, the SAGs are to promote capacity building though
training and education at GAW stations in developing countries, particularly during the early operation at newly established stations. This is done
through matching those stations or individuals in need of help with experienced laboratories or scientists to provide the needed support.
Such “twinning” of the experts with the inexperienced is a critical component to achieve high quality data from stations in
countries without the local expertise.
GAW is implemented in accordance with the principle that when a country agrees to participate, full responsibility for its GAW activities rests
with that country. WMO does not, for example, cover the costs of long-term maintenance of GAW stations and facilities. Nevertheless, many
developing countries require outside support to start, or improve their participation in the GAW programme. In recognition of this, WMO has provided
limited support for developing countries through a variety of methods whenever funds are available. Capacity building is of critical importance to
GAW and is provided through workshops, reports, consultant services, and onsite training by outside experts. WMO also has encouraged its Member
countries to include GAW projects in their UNDP national programmes, and to enter “twinning” arrangements where, on a bilateral
basis, a laboratory, institute or an experienced individual scientist sponsors measurements of specific parameters at a station or group of stations
in developing countries. Whenever funds can be made available, the WMO also provides limited support for the maintenance of instruments through
calibrations, repairs and upgrades. Also, measurements have been initiated in data sparse regions and new GAW stations have been established by
the WMO thorough international funding mechanisms.
Space-based observations offer a partial solution toward the goal of achieving global coverage of certain measurements important to the GAW
programme. These measurements include ozone (column and profile), solar radiation, and surface measurements of some trace gases such as
carbon monoxide as well as ancillary parameters. Satellite observations are of benefit to the global community and are of special interest to
those geographic regions where there are gaps in GAW's surface-based monitoring network. For this reason integration of satellite observations
into the GAW programme is highly desirable. In turn, satellite systems can best meet their established requirements if they are checked against
highly accurate ground based measurements of known quality. The GAW network of stations have provided both total column ozone and vertical
profile ozone data for satellite validation for the past few decades. A new generation of satellites sensors have begun operation and presently
include the capability to make free tropospheric measurements of carbon monoxide and column methane. A few of the high altitude GAW stations
measure carbon monoxide and could be of value for checking the accuracy of these relatively new satellite measurements.
In addition to the GAW monitoring programme, the WMO GAW Urban Research Meteorology and Environment (GURME) project was recently
started in response to the requests of the National Meteorological and Hydrological Services (NMHSs). The lead responsibility for the programme
rests with the Scientific Advisory Group (SAG GURME). NMHSs have an important role to play in the study and management of urban environments
because they collect information and have capabilities that are essential to the forecasting of urban air pollution and the evaluation of the effects
of different emission control strategies. The WMO established GURME as a means to help enhance the capabilities of NMHSs to handle meteorological
and related aspects of urban pollution. GURME is designed to do this through co-ordination and focussing of present activities, as well as
initiation of new ones.
In April 2001, the EC Panel approved a new strategic plan for GAW and is given in the WMO/GAW Report #142 “Strategy for the Implementation of the Global Atmosphere Watch Programme (2001-2007)”. This report includes a list of 8 strategic goals:
(a) Improve measurements programme for better geographical and temporal coverage and for near real time monitoring capability,
(b) Complete the quality assurance/quality control system,
(c) Improve availability of data and promote their use,
(d) Improve communication and co-operation between all GAW components and with the scientific community,
(e) Identify and clarify changing roles of GAW components,
(f) Maintain present and solicit new support and collaborations for the GAW programme,
(g) Intensify capacity building in developing countries,
(h) Enhance the capabilities of NMHSs in providing urban-environmental air quality services.
Over the lifetime of this Strategic Plan, human activities will continue to change the composition of the atmosphere, although efforts will be made to control them. The WMO GAW network of stations must continue to monitor the critical atmospheric parameters and provide scientific data needed to understand and ultimately predict environmental changes on both regional and global scales. As GAW continues to mature, closer co-operation with SPARC and with other organisations closely tied to the use of these data, needs to be developed.