For the human-biometeorologically significant assessment of the thermal component of the urban climate, the application of thermal indexes which are based on the human energy balance is recommended. For the assessment of single air pollutants, standards exist in almost every country of the world. However, these standards are insufficient in view of the persistent demands (e.g. from urban planners) for the assessment of air quality, which is not limited to a single air pollutant.

Consequently, various air quality indexes are available worldwide. They can be categorized into two groups. The first group includes indexes, which are expressed as the sum of relative concentrations of air pollutants easily available for a long time period. These indexes do exist for short or long-term conditions. However, these indexes are disadvantaged, since they are only statistical and have no relation to humans. Therefore, they indicate mainly the content of air pollution in the ambient air.

Impact-related indexes constitute the second group. Such indexes are very rare, because it is difficult, to quantify the impacts of air pollutant which are quite different for short and long-term conditions on humans. A new impact-related air quality index obtained on a daily basis and abbreviated as TLQ (in German: TagesLuftQualitätsindex) was jointly developed and tested by the Meteorological Institute, University of Freiburg, and the FoBiG company in Freiburg. It considers SO2, CO, NO2, O3 and PM10. Their concentrations are divided into six ranges following results of toxicological investigations for each air pollutant and corresponding standards of the European Union.

In the presentation, the method of determining TLQ will be exactly described. In addition, results of test calculations carried out for TLQ as well as one type of a daily statistical index will be discussed. The basis for the test calculations were half-hourly mean values of SO2, CO, NO2, O3 and PM10, which were recorded at two different urban and one rural air quality monitoring stations in south-west Germany from 1996 to 1998. The results of the test calculations give first indications of how the feelings of people are reproduced by both air quality indexes.