This is a close up of the filter carousel in the filter rack. The sample air goes through the large white impactor in the center of the picture (impactor is made of stainless steel, but has protective plastic cover), through the carousel (bottom center) and then to the active filter. The tubes exiting the carousel and going toward the top of the picture are the vacuum tubing. Vacuum to the individual filters is controlled by a set of 8 solenoids (not shown).

The filter rack consists of a filter carousel with 8 filters. Seven of the filters are operated consecutively over a 24 hour time period in order to obtain daily chemistry samples, one for each day of the week. The eighth sample serves as a field blank. Quick-connect fittings are used to make the weekly filter changing easier for field operators.