[Variance of the air sample in air analysis demonstrated on a sample of atmospheric aerosol].

Particulate matter, sampled during 24-h periods from 200 m-3 urban air, was collected on cellulose filters. Each of the four quarters of the filters was analyzed separately by atomic absorption spectroscopy; the concentration of 11 metals was so determined. The residual standard deviation among the quarters of the filter was 10%. In view of this deviation among the results, attributed to the variance of the air sample, it seems rather doubtful that the intercomparison of air sampling instruments, using ambient air as common "standard", will ever give reliable results. It seems likely that air samples, smaller than the 200 m-3 used here, will show an even greater variance, at least with regard to some specific pollutants.