capable of measuring 24-hour PM10 mass concentrations of at least 300 micro-g/std m3
while maintaining the operating flow rate within the specified limits.
4.0 Precision.
4.1 The precision of PM10 samplers must be 5 micro-g/m3 for PM10 concentrations below 80
micro-g/m3 and 7 percent for PM10 concentrations above 80 micro-g/m3, as required by
Part 53 of this chapter, which prescribes a test procedure that determines the variation in the
PM10 concentration measurements of identical samplers under typical sampling conditions.
Continual assessment of precision via collocated samplers is required by Part 58 of this
chapter for PM10 samplers used in certain monitoring networks.
5.0 Accuracy.
5.1 Because the size of the particles making up ambient particulate matter varies over a wide
range and the concentration of particles varies with particle size, it is difficult to define the
absolute accuracy of PM10 samplers. Part 53 of this chapter provides a specification for the
sampling effectiveness of PM10 samplers. This specification requires that the expected mass
concentration calculated for a candidate PM10 sampler, when sampling a specified particle
size distribution, be within +/-10 percent of that calculated for an ideal sampler whose
sampling effectiveness is explicitly specified. Also, the particle size for 50 percent sampling
effectiveness is required to be 10+/-0.5 micrometers. Other specifications related to accuracy
apply to flow measurement and calibration, filter media, analytical (weighing) procedures, and
artifact. The flow rate accuracy of PM10 samplers used in certain monitoring networks is
required by Part 58 of this chapter to be assessed periodically via flow rate audits.
6.0 Potential Sources of Error.
6.1 Volatile Particles. Volatile particles collected on filters are often lost during shipment and/or
storage of the filters prior to the post-sampling weighing3. Although shipment or storage of
loaded filters is sometimes unavoidable, filters should be reweighed as soon as practical to
minimize these losses.
6.2 Artifacts. Positive errors in PM10 concentration measurements may result from retention of
gaseous species on filters4,5. Such errors include the retention of sulfur dioxide and nitric acid.
Retention of sulfur dioxide on filters, followed by oxidation to sulfate, is referred to as artifact
sulfate formation, a phenomenon which increases with increasing filter alkalinity6. Little or no
artifact sulfate formation should occur using filters that meet the alkalinity specification in
section 7.2.4. Artifact nitrate formation, resulting primarily from retention of nitric acid, occurs
to varying degrees on many filter types, including glass fiber, cellulose ester, and many quartz
fiber filters5,7,8,9,10. Loss of true atmospheric particulate nitrate during or following sampling
may also occur due to dissociation or chemical reaction. This phenomenon has been observed
on Teflon(R) filters8 and inferred for quartz fiber filters11,12. The magnitude of nitrate artifact
errors in PM10 mass concentration measurements will vary with location and ambient
temperature; however, for most sampling locations, these errors are expected to be small.
6.3 Humidity. The effects of ambient humidity on the sample are unavoidable. The filter
equilibration procedure in section 9.0 is designed to minimize the effects of moisture on the
filter medium.
6.4 Filter Handling. Careful handling of filters between presampling and postsampling weighings is
necessary to avoid errors due to damaged filters or loss of collected particles from the filters.
Use of a filter cartridge or cassette may reduce the magnitude of these errors. Filters must
also meet the integrity specification in section 7.2.3.
6.5 Flow Rate Variation. Variations in the sampler's operating flow rate may alter the particle size
discrimination characteristics of the sampler inlet. The magnitude of this error will depend on
Terms of Use | Privacy Policy | DMCA Policy
2006-2020 Rsmanuals.com