 threshold values are of prime importance in providing a sound basis for public health decisions . 
 a key issue is determining threshold or maximum exposure values for pollutants and assessing their potential health risks . 
 environmental epidemiology could be instrumental in assessing these levels , especially since the assessment of ambient exposures involves relatively low concentrations of pollutants . 
 this paper presents a statistical method that allows the determination of threshold values as well as the assessment of the associated risk using a retrospective , longitudinal study design with a prospective follow - up . 
 morbidity data were analyzed using the fourier method , a time - series analysis that is based on the assumption of a high temporal resolution of the data . 
 this method eliminates time - dependent responses like temporal inhomogeneity and pseudocorrelation . 
 the frequency of calls for respiratory distress conditions to the regional mobile medical emergency service ( mmes ) in the city of leipzig were investigated . 
 the entire population of leipzig served as a pool for data collection . 
 in addition to the collection of morbidity data , air pollution measurements were taken every 30 min for the entire study period using sulfur dioxide as the regional indicator variable . this approach allowed the calculation of a dose - response curve for respiratory diseases and air pollution indices in children and adults . 
 significantly higher morbidities were observed above a 24-hr mean value of 0.6 mg so2/m3 air for children and 0.8 mg so2/m3 for adults.(abstract truncated at 250 words)imagesfigure 1.figure 2 . 
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