A NEW CASCADE IMPACTOR FOR AEROSOL SAMPLING WITH SUBSEQUENT PIXE ANALYSIS

A small deposit area low pressure impactor (abbreviated to SDI) has be en developed and tested. The device has been designed specifically to collect size-fractionated aerosol samples in remote locations for subs equent chemical analysis by PIXE. The SDI is a 12-stage, multinozzle d evice, but the deposit for each stage remains confined to an area with diameter less than 8 mm. It operates at a flow rate of 11 L/min and a ccepts the same, 25 mm diameter substrate rings as the PIXE Internatio nal cascade impactor. The experimental cut-points for stages 12 throug h 1 are 8.50, 4.08, 2.68, 1.66, 1.06, 0.796, 0.591, 0.343, 0.231, 0.15 3, 0.086 and 0.045 mu m equivalent aerodynamic diameter. The SDI has b een tested in (and employed for) size-fractionated aerosol sampling in the Finnish Arctic and at Summit in Greenland. The data show that the SDI gives results very similar to those obtained with the PIXE Intern ational impactor, but with detection limits that are much lower. This suggests that the SDI can be used with shorter sampling times or in ar eas where concentrations are smaller to obtain reliable size distribut ion data. The results also suggest that data for a greater number of e lements can be obtained with the SDI.