SPARTAN update

At the moment it seems that the SPARTAN instrument will be designed as a stacked filter unit. I found the following image on an Australian Government website with a very similar design scheme. This is good news, as I wasn't sure if our instrument had any precedent (i.e. for using two stacked filters preceded by a impaction plate) Another group has been in charge of the the design stage hence why I did not know more about this general approach.

Stacked filter unit with a very similar design to our own (except that we will have eight columns instead of just one). 

Regarding the coarse and fine filters (separating the "PM2.5" and PM10-PM2.5 mass fractions), we ordered some filters from SPI to do the job: a 47 mm diameter grease-coated membrane filter (part# E4708G-MB with 8um holes, $550 per 100-pack) and a 25mm polycarbonate membrane filter (part # E0425-MB with 0.4 um holes, $70 per 100 pack).

These filters are Nuclepore in spirit but without the eponymous brand name. They are both made of polycarbonate with etched holes to trap coarse and fine particulates, respectively. Notice how much more the 47 mm filters cost. This is due to the grease coating used to prevent bounce-back. I don't know how bad the bounce back is in a straight-shot filter yet it has been argued enough to necessitate the extra cost of the greased filters. I don't know if grease would benefit the smaller size fraction as well. Also the coated disks come in 47 mm diameters only, so we needed to cut them down to size. There were many email discussions about cutting filters in a replicable way, i.e. we need to pre weigh filters accurate to 1 microgram so piece can't be later falling off. The plan is proceed using a sharp steel punch (made courtesy of the workshop in the Dunn basement) sandwiched between two filter papers.

Otherwise the filters look good; the 25 mm filters allows an air flow rate up to 62.5 litres per minute and stable until about 140 degrees Celsius and the coarse filter is much the same. As we are operating these at 4.0 lpm and a temperature between 5-40 degrees, there should be no issue with these parameters.