Secretion of GM-CSF by 16HBE cells exposed for 24 hrs to the different size-fractions (UF: PM
, F: PM
, I: PM
and C: PM
). a) isomass exposure at 1 or 10 μg/cm2: The data from seven size-segregated aerosol samplings were pooled and are presented as box plots. Each box plot is composed of 3 horizontal lines displaying the 25th, 50th and 75th percentiles. Minimal and maximal values are plotted as a dot. n = 82 for control, n = 20 for each size-fraction and dose. b) isovolume exposure: As the volumes of particle suspensions applied to cells were different for each experiment, average values could not be calculated. Representative experiments for winter (W) and summer (S) LPI samplings are presented. Volumes applied to cells were determined in order to get either 1 (isovol1) or 10 (isovol10) μg/cm2 of ultrafine particles. For each fraction, the corresponding concentration in mass is given in μg/cm2. Similar results were obtained for each of the 7 samplings. Values are mean ± SD. n = 55 for control, n = 4 for each size-fraction. * different from control (p < 0.05), ° different from lower concentration (p < 0.001), different letters indicate significant difference between size-fractions within each concentration for isomass exposure (p < 0.001).