Tisch Environmental 1-TSP-AND-PM10 sales@tisch-env.com www.tisch-env.com Page 37 of 183
Field Blanks
Field blanks are conditioned, weighed and clean unexposed filters that are
used to determine if contamination occurs during sample setup, recovery and
transport. Field blanks occur at 10% of the sampler’s operating routine. Field
blanks should be scheduled to ensure that a post weighing session contains
10% of blanks or at least (1) field blank.
Field blanks are taken out to the sampler, removed from their protective
container and installed into the filter holder like a normal sample is. They are
left there momentarily (a minute or two) then removed and placed back into
their protective container. They are then left in the sampler’s enclosure while
the sampler is running a sample. Field blanks are retrieved along with the
sample and weighed in the lab to determine if any contamination occurs in the
Lab Blanks
Lab blanks are clean, conditioned filters that are used to determine if any
contamination or weight change is happening in the pre and post weighing
functions in the laboratory. Laboratory blanks should be kept inside the
conditioning chamber except during weighing. Each post-weighing session
should include at least one laboratory blank. If the weight of the laboratory
blank changes more than 15µg, there is contamination of the filters during the
weighing process that need to be investigated and resolved.
4.8 Filter Pre-Conditioning and Weighing
NOTE: For PM10 and PM2.5 sampling, refer to EPA QA Guidance Document
2.12 Monitoring PM2.5 in Ambient Air Using Designated Reference for
Class I Equivalent Methods for information on filter weighing, conditioning
and microbalance standards.
Conditioning of clean unexposed filters
New, unexposed filters must be conditioned in a conditioning environment for
24 hours before the pre-weighing. The mean %RH must be between 30 and
40 %RH ±5% over the 24 hours of conditioning and a mean temperature
between 20 and 23ºC with a variability of no more than ±2ºC over the 24 hour
conditioning period.
In the conditioning chamber the filter should be placed on a covered rack or
an open-sided cabinet that will allow circulation over the filters while
reducing the chance that airborne particulates will get onto the filters.
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