General introduction and objectives of TEMIS

 
Contents of this page:

• The changing composition of the Earth's atmosphere
  • Ozone and UV
  • Greenhouse effect
  • Air pollution
• Satellite observations of tropospheric trace gases
• Objectives of the TEMIS project
  • Involvement of users and internet service

The changing composition of the Earth's atmosphere

The composition of the atmosphere has undergone dramatic changes since pre-industrial times due to increased emissions related to human activity, e.g. industry, transport, heating, changed land use and agriculture, biomass burning. These atmospheric changes are manifesting themselves through aspects like climate change (heating of the Earth related to greenhouse gases such as CO2 and CH4), air pollution (e.g. smog, acid rain), ozone depletion and the ozone hole. In response to this, several international agreements and protocols have emerged, such as the Montreal and Kyoto protocols.

Monitoring of atmospheric trace gases is of importance to quantify the concentrations of atmospheric trace gases. Based on solid observational data, and the global information provided by satellite instruments, top-down estimates can be made of the world-wide distribution of anthropogenic and natural emissions. The extension of the present-day monitoring network with new satellite observations will be important, given that emission inventories are characterised by large uncertainties. Observational data sets will provide the quantitative background knowledge to assess the implementation of present protocols, and they will form the basic source of information for future protocols.
 
Ozone and UV  
In the years following the discovery of the Antarctic ozone hole, the cause of the breakdown of ozone has been convincingly attributed to the emissions of chlorofluorocarbons (CFC's). The Montreal protocol and later amendments have led to a strong decrease in the production of man-made CFC's, which is expected to result in the recovery of the ozone layer in the coming decades. The amount of harmful ultraviolet (UV) radiation that will reach the Earth's surface is directly related to the thickness of the UV absorbing ozone layer (between 10-40 km altitude). Satellite monitoring of the ozone layer lies at the basis of UV analysis and UV index forecast.
 
Greenhouse effect  
Several gases in the Earth's atmosphere - such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3) and the chlorofluorocarbons (CFC's) - trap infrared radiation, which leads to heating of the lower atmosphere and the Earth's surface: the greenhouse effect. Also small atmospheric particles, aerosols, have a large but difficult to quantify impact on the radiation budget. The Kyoto protocol discusses measures that would result in a reduction of the emissions of CO2> and other greenhouse gases.
 
Air pollution  
Air pollution has become a global issue. Much of the anthropogenic air pollution travels long distances and affects areas far from the emission source. Air pollution results in health effects for humans, has a damaging effect on flora and fauna, and causes acid rain. It is related to the large-scale fossil fuel combustion and fossil-fuel related activities, but also to biomass burning and changes in land use. The emissions of oxides of nitrogen (NO and NO2) and sulphur (SO2) leads to acid rain and result in photochemical smog and ozone formation.

The TEMIS project will contribute to these central issues by generating data sets of several key species and by providing free access to these data sets via internet.

Satellite observations of tropospheric trace gases

Satellite missions such as the Upper Atmosphere Research Satellite (UARS) of NASA have greatly contributed to a detailed understanding of the processes responsible for the breakdown of ozone. Such missions have measured many different species, such as ozone, nitrogen oxides, and the important chlorine containing gases. A global view has emerged of the atmosphere between 15 and 40 km, the stratosphere. The NASA TOMS instrument data record goes back to 1979, and provides a unique sequence of the evolution of the ozone layer from the pre-ozone hole period to the present.

Measurements of the chemical composition of the troposphere (0-15 km altitude) by satellites are much more rare. Even the prime gas ozone is still poorly known in the lower part of the atmosphere. Considerable efforts to deduce tropospheric ozone from the TOMS data have led to convincing results only in a narrow belt around the equator.

Envisat is a new European satellite that will be launched early 2002. With dedicated instruments such as SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric CartograpHY), Envisat aims at improving this lack of tropospheric data by measuring a large number of trace gases. The list of products includes many of the key species mentioned above: ozone (with explicit vertical profile information), nitrogen dioxide, formaldehyde, carbon monoxide, methane, sulphur dioxide, bromine monoxide and aerosols.

The capabilities of SCIAMACHY have been convincingly demonstrated by the instrument GOME (Global Ozone Monitoring Experiment; 1995-present), part of the European ERS-2 satellite. The achievements of GOME include: the discovery of tropospheric BrO plumes in the polar planetary boundary layer, global mapping of ozone and the ability to provide information on the vertical distribution of ozone, a global monitoring of tropospheric NO2 and formaldehyde (CH2O), the observation of SO2 emitted by active volcanoes and by industry, and the detection of aerosols. GOME has also highlighted several fundamental difficulties in the derivation of these tropospheric products from the spectra measured by GOME and SCIAMACHY. The derivation of quantitative data sets with a high accuracy will be a major challenge for the future.

Objectives of the TEMIS project

Within the TEMIS project, long-term data sets will be generated for ozone, UV, aerosols and several of the trace gases mentioned. Advanced retrieval techniques, chemistry transport modelling and data assimilation techniques will be used to derive high-quality tropospheric products based on the mesaurements of SCIAMACHY and GOME. These data sets will be made freely available through a user-friendly interface.
 
Involvement of users and internet service  
The implementation of the TEMIS service will result from direct interactions with parties interested in the tropospheric satellite data products. The final choice of data sets that will be delivered through the TEMIS internet service will depend on the requests and requirements from these users.