2.1 Nucleopore polycarbonate filter
For the investigations in this RCA programme, Nucleopore filters have been chosen as the filter media.
The filter that collects the coarse airborne particulate matter particles is a 47 mm diameter Nucleopore track etched polycarbonate filter with a pore size 8 µm. These coarse filters are coated with Apiezon Type L grease (refer to the next chapter for details on coating the filters with Apiezon), the purpose of the coating is to provide a tacky surface that prevents particle rebound and consequent sample loss. It is important to the method that coated filters must be used [3].
The second filter collects PM2.5-0 particles is also a 47 mm diameter Nucleopore polycarbonate filter but with a pore size of 0.4 µm. Note that the PM2.5-0 Nucleopore filters are not coated with Apiezon.
Figures 4 and 5 show scanning electron microscopy (SEM) images of coarse and fine Nucleopore polycarbonate filters on which air particulate matter from the Wellington region, New Zealand, have been caught. The pores appear as black holes in the image.