9. Zero the microbalance before all weighings. Use the same microbalance for weighing filters
before and after sample collection. Calibrate the balance with National Institute of Standards and
Technology Class S-1.1 or ASTM Class 1 weights.
10. The set of replicate field samples should be exposed to the same dust environment, either in a
laboratory dust chamber [8] or in the field [9]. The quality control samples must be taken with the
same equipment, procedures, and personnel used in the routine field samples. Calculate precision
from these replicates and record relative standard deviation ( ) on control charts. Take corrective
action when the precision is out of control [8]