Correcting TEOM Measurements using the KCL Volatile
Correction ModelDavid Green, Gary Fuller
& Timothy Baker
2 Presented by David Green
Contents
• Model Development Context• UK PM Monitoring Problem• Model derivation• Model testing• Proposed monitoring strategy for
the UK
3 Presented by David Green
Model Development Context
• January LAQN Seminar – London FDMS• Defra funded work early 2007
–Grounded in statistics used to demonstrate equivalence
– UK wide applicability
• Named it: “Volatile Correction Model”• Future steps
4 Presented by David Green
PM10 Monitoring Problem• Complex pollutant
– Different components
– Constantly changing
• Reference Method– Labour intensive
– Poor time resolution
– Slow data dissemination
Reference
MethodTEOM
FDMS
• TEOM– Heats sample inlet to 50°C to
eliminate water but looses volatile PM
• FDMS– Uses a diffusion dryer to eliminate
water and retain a sample temperature of 30°C
– Equivalent to Reference
• UK Monitoring Networks– Predominately TEOM
– Need to use equivalent methods for reporting to EU
BAM
5 Presented by David Green
PM10 Measurement Time Series
0
10
20
30
40
50
60
70
28/11/04 28/01/05 28/03/05 28/05/05
Da
ily
Me
an
Co
nc
en
tra
tio
n (
µg
m-3
)KFGTEOM
6 Presented by David Green
PM10 Measurement Time Series
0
10
20
30
40
50
60
70
28/11/04 28/01/05 28/03/05 28/05/05
Da
ily
Me
an
Co
nc
en
tra
tio
n (
µg
m-3
)KFGTEOMFDMS
7 Presented by David Green
PM10 Measurement Correlation
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Reference Method (µg m-3)
Ca
nd
ida
te M
eth
od
(µ
g m
-3)
TEOM
FDMS
8 Presented by David Green
How do we achieve an Equivalent Network?
• Upgrade TEOM to FDMS–Expensive (capital)
–Retains some continuity of measurement
• Change monitoring equipment–Gravimetric
– (capital and revenue)
– Loose continuity of measurement
–Delay in reporting time
–BAM–Expensive (capital)
– Loose continuity of measurement
• A ‘Third Way’?–Using FDMS measurements of volatile PM to
correct TEOM measurements
9 Presented by David Green
KCL Volatile Correction Model
• Provides a daily, site specific correction factor for TEOM measurements
• Correction based on FDMS purge measurement made some distance away
• Results in reference equivalent daily mean concentration within the 25% expanded uncertainty specified by the AQ Directive
11 Presented by David Green
FDMS – Filter Dynamics Measurement System
• 2 measurement modes:–Base (analogous to
standard TEOM)
–Purge, which measures mass lost from the filter when particle free air is passing through it
• FDMS Mass = Base - Purge
14 Presented by David Green
TEOM – Base vs. FDMS Purge
-25
-20
-15
-10
-5
0
5
23/12/2004 20/01/2005 17/02/2005 17/03/2005 14/04/2005 12/05/2005 09/06/2005
Co
nce
ntr
atio
n (
µg
m-3
)
Birmingham TEOM-Base Birmingham Purge
15 Presented by David Green
TEOM – FDMS Base vs. FDMS Purge
-25
-20
-15
-10
-5
0
5
-25 -15 -5 5
TEOM - FDMS Base (µg m-3)
FD
MS
Pu
rge
(µg
m-3
)
16 Presented by David Green
PM10 Measurements
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Reference Method (µg m-3)
Ca
nd
ida
te M
eth
od
(µ
g m
-3)
TEOM
FDMS
17 Presented by David Green
PM10 Measurements
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Reference Method (µg m-3)
Ca
nd
ida
te M
eth
od
(µ
g m
-3)
TEOM
FDMS
Model
19 Presented by David Green
Uniform FDMS Purge Concentrations
-25
-20
-15
-10
-5
0
5
23/12/2004 20/01/2005 17/02/2005 17/03/2005 14/04/2005 12/05/2005 09/06/2005
Co
nce
ntr
atio
n (
µg
m-3
)
Bexley Purge North Kensington Purge Marylebone Purge
20 Presented by David Green
Equivalence Testing
• Experiment 1 – test the model at the equivalence programme sites excluding regional aspects
• Experiment 2 - test the model at the equivalence programme sites including regional aspects
Criteria
n ≥ 40
n ≥ 50 % of limit value ≥ 25%
Between reference sampler uncertainty
≤ 2 µg m-3
Between candidate sampler uncertainty
≤ 3 µg m-3
Expanded Uncertainty ≥ 25%
22 Presented by David Green
Expanded Uncertainty
0
10
20
30
40
50
60
70
80
90
0 200 400 600
Distance (km)
Exp
and
ed U
nce
rtai
nty
(%
)
Model
FDMS
24 Presented by David Green
Conclusion
• Model provides a daily, site specific correction factor for TEOM measurements to provide a reference equivalent measurement:
Reference Equivalent PM10 = TEOM – 1.87 FDMS purge
• Works up to a distance of 200 km• Allows smaller number of FDMS instruments
to correct larger network of TEOMs–Financial and data continuity implications
• Further work…
25 Presented by David Green
Further Work
• Physical and chemical basis for model–Concentrations on TEOM and FDMS filters
–Ammonium nitrate
–Volatile organic compounds
–Collocated measurements–Ammonium nitrate
–Volatile organic compounds
–Water
• Extend to hourly public dissemination• Provide method for local authorities to use the
model• Extend to PM2.5
26 Presented by David Green
Acknowledgements
• Defra• London Borough of Bexley• London Borough of Greenwich• London Borough of Ealing• City of Westminster• Royal Borough of Kensington and
Chelsea• Air Monitors