Air quality expert group - Fine particulate matter (PM2.5) in ... - Defra

humidity changes or the slow accumulation of water or other material, such
as semi-volatile organic matter or reactive gases, unrelated to the pumped
sampling, and this will be interpreted as changes to the PM mass. There is no
ideal filter material, and the mass change can vary between different batches of
the same filter material. EN 14907 allows filters made from quartz fibres, glass
fibres, PTFE-coated glass fibre and PTFE membrane to be used.
2.2.2 Equivalent methods
Measuring PM2.5 and its components
17. The reference methods for PM2.5 are not capable of producing real-time data,
and neither the low volume or high volume version has been used to produce
the data used in this report. The EU allows the use of equivalent methods for
regulatory purposes, where equivalence is defined within the Guide to the
Demonstration of Equivalence (2010). This sets out a procedure for quantifying
the agreement between reference and non-reference methods over a series of
parallel field measurements. The objective is that equivalent instruments should
produce daily data with a measurement uncertainty less than that required
in the Ambient Air Quality Directive (±25% with a 95% level of confidence)
at concentrations close to the limit value. Given the nature of the definition
of PM2.5, these equivalent methods will in general have the same limitations
as the reference method (which they must agree with), together with further
limitations specific to the equivalent methods.
18. A major exercise within the UK in 2006 (Harrison et al., 2006) found that the
automatic instruments Filter Dynamic Measurement System (FDMS) (made
by Thermo) and Beta Attenuation Monitor (BAM) (made by Met-One) could
be used as equivalent instruments for PM2.5 measurement. Virtually all of the
automatic data within this report are from FDMS instruments (described in
Section 2.3.2).
19. Other PM2.5 data are presented from non-reference manual gravimetric samplers
known as Partisols. These have a lower sampling flow than the low volume
reference method, at 1 m 3 hr -1 , but the same sized 47 mm diameter filters.
These have not been shown to be equivalent for PM2.5 data, although they have
for PM10.
2.2.3 Current developments relating to the reference method
20. In view of the regulatory requirements and the experience gained with PM
measurement issues in recent years, CEN is currently producing two new
standards. The first is a revised version of the standard methods for both PM2.5
and PM10, so that EN 14907 and EN 12341 will be combined. The aim of this
is to reduce the scope for variations in results allowed within the methods,
without causing any significant discontinuity with earlier results. The second
is a new standard covering automatic methods. In effect this will bring the
procedures in the Guide to the Demonstration of Equivalence (2010) into a
formal standard, and also set out requirements for ongoing quality assurance
and quality control, bringing PM CEN standards more in line with those for
gaseous pollutants.
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