Good field observations are the needed to establish a clear record of what is happening to pollutants in the atmosphere, to provide a basis for an empirical interpretation of the processes involved and to verify the computer models used to describe the transport and reactions in a quantitative manner.
EUROTRAC has 4 field measurement subprojects
In order to understand and model the complex reaction sequences which occur in the atmosphere, it is necessary to have good estimates of the characteristics of the individual reactions. These must be investigated in the laboratory and require the study of reactive intermediates with lifetimes as short as a few nanoseconds.
Two subprojects are devoted to the study of fundamental chemical processes leading to atmospheric pollution.
Trace substances abound in the atmosphere; some arise from man's activities and, because of their quantity, are regarded as pollutants; others arise from natural biological processes in vegetation and in fresh and sea water. Some natural substances can, under the appropriate conditions, also be precursors for pollutants, and it is important in assessing the composition of the air to distinguish clearly between man- made and natural contributions.
The sea, earth and vegetation are also the final sinks for all emitted compounds, so in order to understand the concentrations of trace substances found in the air it is necessary to know the rates at which compounds are deposited on the different surfaces available.
Two projects are involved in the study of emission and deposition processes in natural environments
In principle numerical computer models embody our knowledge of the atmosphere and the trace substances and pollutants it contains. In the future it will be possible to use them to describe and predict the occurrence of summer smog or the deposition of acidity in particular areas. In practice the present models themselves contain many simplifications and assumptions which have to be explored and tested, and the models themselves have to be verified against observations before they can be relied upon with confidence.
Models are used throughout EUROTRAC from the strictly local scale, in order to interpret the results of an individual experiment or study of the pollutants in a small geographical area, up to the global scale where the contribution of Europe to the global pollution burden is studied.
Two projects are devoted specifically to modelling: EUMAC which is the central modelling subproject of EUROTRAC, and GLOMAC which uses 3-dimensional global models to study the transport of pollutants world wide.
GENEMIS , the newest subproject, produces emission data with a high temporal and spatial resolution which are used as indispensable input data for the models.
The ability to measure and monitor trace substances and pollutants, which have such chemically small concentrations in the atmosphere, depends on the availability of suitable and reliable instrumentation. Advances in understanding have often followed improvements in apparatus and technique. Development of improved instrumentation was seen from the beginning as an essential part of EUROTRAC.
Three EUROTRAC subprojects: