CASTNET Field Blank Filters
Marcus O. Stewart
MACTEC Engineering & Consulting Inc.,
Newberry, FL USA
CASTNET utilizes an open-face, three-stage filter pack to measure sulfur and nitrogen species. Filter pack handling procedures are designed to minimize handling and, consequently, reduce any opportunities for contamination and misdirection. Sample integrity is maintained by ensuring that materials in contact with filters do not affect measured analytes. Field blanks are used to assess the sample integrity during the packing, shipping, receiving, and unpacking phases of the operation.
Field blanks are prepared quarterly for each CASTNET site. The filter packs used for the field blanks contain a nonstandard connection that cannot be installed in the sampling system in the field. The filter pack with the field blank is prepared and loaded according to standard CASTNET procedures. The field blanks are clearly identified and labeled to prohibit their removal from the resealable plastic bag used for shipping. When the field blank filter is returned from a site, it is unpacked, extracted, and analyzed following procedures for exposed filters. The field blank program and results for 2007 are summarized in the poster.