Abstract

Particulate ions in air are collected by low volume samplers on filters containing low levels of these ions. The mean concentration found in extracts of blank filters compared to the mean concentration of loaded filters, collected largely in 1990, is 37% for chloride, 6% for nitrate, 7% for sulphate and 31% for ammonium. Three blank correction methods are evaluated. The correction method with the mean of 8 blank filters of the adjacent period gives a trend compensation with an negligible increase of the random error. Comparison of the ion concentrations found in field blanks (A), with ion concentrations found in blank filters itselves (B) showed no differences. Contamination caused by the extraction procedure could not be demonstrated.