SANDWICH Material Balanc

Approach for PM2.5 Data Analy

Neil Frank OAQPS/USEPA

For Presentation at

2006 National Air Monitoring Conference

Las Vegas, Nevada

November 6-9, 2006
Outline

• What is “SANDWICH”, why it is goo

to describe PM2.5 composition

• How it can help with PM2.5 data QC• Examples using STN data
Introduction

• What is the SANDWICH Approach?

– Sulfate, Adjusted Nitrate, Derived Wat

Inferred Carbon Hybrid material balanc

approach 

• for estimating PM2.5 mass composition pr

by the PM2.5 FRM.

– The approach uses a combination of 

speciation measurements and modelespeciation estimates to represent FRM 
Introduction (cont.)

• Why is it needed?

– The FRM defines the regulatory indicator of P

– FRM mass may not retain all nitrate, and incl

particle bound water and other components nestimated directly with STN measurements.

– To estimate FRM PM2.5 composition includin

carbonaceous mass without “fudge” factors. 

– To help QC speciation measurements

• SANDWICH is the default method in EPA 

modeling guidance to define baseline PM

– for SMAT (

speciation modeled attainment te
Old Practice: Use STN measurements to directly characteriz

These represent a subset of STN speciation measur

FRM and STN measurements

PM2.5 mass SO42- NH4+ NO3- {Al SI Ca Fe T
Sulfate Ammonium Nitrate

Aluminum Silicon Calcium Iron Titaniu

Organic and Eleme

Old Practice: Use STN measurements to directly characteriz

FRM and STN measurements

PM2.5 mass SO42- NH4+ NO3- {Al SI Ca Fe T
(Teflon filter)

FRM sampler

(Nylon following denuder) (Teflon) 

Various Speciation Sampler

* Various STN speciation samplers,with different design and flow rates compared to FRM:

MetOne (SASS), Anderson (RASS), URG (MASS), R&P

FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} 

Old Practice: Use STN measurements to directly characteriz

FRM and speciation samplers have different flow ra

face velocity and monitoring protocols.
Constructed Mass using STN measureme

Sulfate Nitrate

{Crustal} OCM E

Create estimates of major components

Old Practice: Use STN measurements to directly characterize PM2.5 

with limited consideration of the different monitoring protocols

FRM and STN measurements

PM2.5 mass SO4 NH4 NO3

{Al SI Ca Fe Ti} 
Ammonium

Sulfate*

(NH4)2SO4

Ammonium Nitrate* NH4NO3

Cr = 2.2*Al +2.49*Si +1.63*Ca + 2.42*Fe +1.94*Ti

OCM

Typical formulas to estimate major components

Old Practice: Use STN measurements to directly characterize PM2.5 

Create estimates of major components

FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} 

Constructed Mass using STN measurements (R

Sulfate + Nitrate + {Crustal} + OCM + 
Ammonium

Sulfate*

(NH4)2SO4

Ammonium Nitrate* NH4NO3

Cr = 2.2*Al +2.49*Si +1.63*Ca + 2.42*Fe +1.94*Ti

OCM=

Old Practice: Use STN measurements to directly characterize PM2.5 

Constructed Mass using STN measuremen

Sulfate + Nitrate + {Crustal} + OCM + 

Create estimates of major components

FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} 

to account for O, H, N in C compounds

From STN field blanks. Imp
Carbonaceous Mass from measured C 

is a very uncertain calculation

k*(OC-b)+EC, e.g. k=1.4 or 1.8

Many Sources of error

• Analytical uncertainty• Blank correction (avg value ~1-1.5ug/m3 OC, ST

sites)

– Varies among our 5 different EPA urban speciation sa– We can’t do site or seasonal adjustments– NOTE: this is a minor issue with IMPROVE data

ug C/ filter ug C/m3

MetOne (SASS) 9.6 14.8 1.5Anderson (RAAS) 10.4 13.5 1.3R&P 2300 14.4 16.1 1.1URG (MASS) 24 7.7 0.3

N

etwor

k

Average 

Total

Carbon on STN Blank Filters* 

24-hr 

sample 

Volume(m3 STN sampler )

5th spe

is the P
Uncertainty of k*(OC-b), conti

• Conversion of OC to OCM (+ 33%), varie

aerosol type and mix

– 1.4 < k < 1.8 ("typical" urban)– 2.0 < k < 2.4 ("typical" rural)

• Weighted average for mixed urban/regional aeroso

– Turpin's estimates based on limited speciatio

• OC- EC split (and unaccounted mass for • Retained carbon mass on FRM teflon vs 

quartz 

– Volatile or other OC may pass thru Teflon

• FRM has higher face velocity than many STN sam

– Water [20-24% of measured PM2.5 water]
Constructed Mass using STN measurements (R

PM2.5 mass

= Sulfate + Nitrate + {Crustal} + O

Bottom line: Measurement data with standard adjustment does not ad

A better use of the STN speciation data to support the PM2.5 

pro

g

Old Practice: Use STN measurements to directly characterize PM2.5 

Approach using measurementsand simple calculatedvalues

Distributeunknown(or scale all down) equally

FRM and STN measurements

PM2.5 mass SO4 NH4 NO3

{Al SI Ca Fe Ti} 
Now, lets modify the STN measurements using SAN

FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} 
Now, lets modify the STN measurements using SAN

FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} 

PM2.5= “Gravimetric” mass• Teflon filters are equilibrated at ~21deg C and 3• Net weight and sample volume are used to prod

The SANDWICH approach considers samplinartifacts and idiosyncrasies of FRM’s gravimemass and STN’s monitoring protocols
FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} OC 

Est. 

H2O

(with AIM)

Reduced NO3(using hourly temp and RH from nearby met station) 

Crustal

(alternative 

formula

which does n

use Al)

FRM Mass(incl. passive, Pa, based on blank=0.5μg/m3)

SO4NH4as reported

Use SANDWICH to characterize PM2.5 SANDW

not direc

AIM (thermodynamic model)or with our response surface equationSee: http://oaqpswww.epa.gov/tom/wiki/pmteam/index.cfm?doc=Water_Calculations

Evaporation model described in my JAWMA 

Frank, N. Retained Nitrate, Hydrated Sulfates, and Cain Federal Reference Method Fine Particulate Matter for 

J. Air & Waste Manage. Assoc. 56 :500–511
FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} OC 

Est. 

H2O

(with AIM)

Reduced NO3(using hourly temp and RH from nearby met station)

Crustal

(alternative 

formula

which does not 

use Al)

Use SANDWICH to characterize PM2.5 

For particle bound water which is part of gravimetric mass

For losses of semivolatile nitrate on FRM filters during sampling

Fpw

For filter contamination(not affected by emissions)

FRM Mass(incl. passive, Pa, based on blank=0.5μg/m3)

SO4NH4as reported
FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} OC 

Est. 

H2O

Reduced NO3(using hourly temp and RH from nearby met station)

Crustal

(alternative 

formula

which does not 

use Al)

OCMmb = FRM – (SO4+NH4+NO3r+H2O+EC+

FRM Mass(includes passive, Pa, based on blank=0.5 ug/m3)

Use SANDWICH to characterize PM2.5 

SO4NH4as reported

OCMmb explicitly accounts for blank correction (sampling artifact), fudge 

account for OC to OCM conversion, H2O & less (non-volatile) OC retain
Cleveland, OH

NO3 Concentration

0.02.04.06.08.0

J FMAMJ J ASOND ann

avg

B

J FMAMJ 

6 Nitrate Study Sites, 2003

FRM doesn’t retain all amb

Monthly and Annual Average NO3, 2003

STN (Measured)

FRM (Measured)

Sulfate Nitrate TCM Crustal Passive

RCFM

(reflects ambient)

SANDWICH

(reflects FRM PM2.5)

0.00.51.01.52.02.5

0.0 

Calculated FRM NO3 

* Note: Chicago has URG sampleambient nitrates. URG has 2 filterfollowed by nylon). The teflon maused by XRF under vacuum prior determination.

FRM (calculated)
ratio of H2O to SO4+NO3+NH4 mass

0.00.10.20.30.40.50.60.70.80.91.0

molar ratio of NH4 to SO4

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

NO3 to SO4 mass ratio0 to 0.10.2 to 0.30.4 to 0.50.6 to 0.70.8 to 0.91.0 to 1.11.5 to 3

Monthly Average Water, ug/m3

01234

Monthly Average Sulfates + Tot

0 3 6 

 Regression Equation: zh2O mod0 = 0 + 0.241578*zso4 plus nh4 mod0

PM2.5 Water Estimated with AIM, using SO4, NO3 

Monthly Average 

tracks Sulfate plus Tot

for 6 study sites, 2

Degree of Neutralization

Using Aerosol Inorganics Model (AIM) at 35% RH and 21o C (no solids are allowhttp://www.hpc1.uea.ac.uk/~e770/aim.html

More water 

with higher % of Sulfates 

or More Acidic Aerosol
EQUATION TO ESTIMATE WATER

(replicates AIM at FRM equilibration conditions)

Let D = NH4

s / SO4, 0<D<0.375, where NH4

s is the amount associated with S

[The corresponding DON ('degree of neutralization', molar) varies from 0 to 2Define relative amounts of SO4, NO3 (reduced) and NH4:

S=SO4/(SO4+NO3+NH4); N=NO3/(SO4+NO3+NH4); A=NH4/(SO4+NO3+NEliminate any excess NH4 not needed to fully neutralize SO4

High acidity: DON <1.2 (D < 0.225 )

Water= [ 595.56 - 1440.58*S - 1126.49*N + 283.91*(S**1.5) - 13.38*(N**1.5) 

- 1486.71*(A**1.5) + 764.23*(S**2) + 1502.00*(N * S) + 451.87*(N**2) - 185.18*(S**2.5) - 375.98*(S**1.5) * N - 16.90*(S**3) - 65.81*(N**1.5) * S 

+ 96.83*(N**2.5) + 83.04*(N**1.5) *( S**1.5) - 4.42*(N**3) + 1720.82*(A**1.5) * S + 1220.38*(A**1.5) * N - 311.50*(A**1.5) * (S**1.5) + 148.77*(A**1.5) * (N**1.5) + 1151.65*(A**3)] * (SO4+NO3+NH4)

Low acidity: DON>1.2 (D>0.225)

Water= [ 202049.0 - 391494.6*S - 390912.1*N + 442.4*(S**1.5) - 155.3*(N**1.5) 

- 293406.8*(A**1.5)+189277.5*(S**2)+377992.6*N*S +188636.8*N**2

- 447.1*S**2.5 -507.2*S**1.5*N -12.8*S**3 +146.2*N**1.5*S +217.2*N**

+ 30.0*N**1.5*S**1.5 - 18.6*N**3 + 216267.0*A**1.5*S + 215419.9*A**1- 621.8*A**1.5*S**1.5 +239.1*A**1.5*N**1.5+95413.1*A**3] * (SO4+NO3

New Development (included in Draft Modeling Guidance)
measurements and modeled estimates

SO4 NH4 NO3r H2O Crustal OCMmb 

Use SANDWICH to characterize PM2.5 

estimates of speciated FRM component

FRM and STN measurements

PM2.5 mass SO4 NH4 NO3

{Al SI Ca Fe Ti} OC 
FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} OC 

PM2.5 mass = SO4 + NH4 + NO3r + H2O + Crustal + OCMm

Use SANDWICH to characterize PM2.5 

By design, perfect mass balance

Sulfate, Adjusted Nitrate, Derived Water, Inferre

Hybrid Material Balance Approach

(SANDWICH)
FRM and STN measurements

PM2.5 mass SO4 NH4 NO3 {Al SI Ca Fe Ti} OC 

SANDWICH and STN measurements

PM2.5 mass = SO4 + NH4 + NO3r + H2O + Crustal + OCMmb 

SANDWICH and STN measurements

PM2.5 mass = Sulfate + Nitrate + Crustal + TCM

Use SANDWICH to characterize PM2.5 

Simpler representation of major componen

By design, perfect mass balance
SANDWICH and STN measurements

PM2.5_mass = SO4 + NH4 + NO3r + H2O + Crustal + OCMm

Pa

SANDWICH and STN measurements

PM2.5 mass = Sulfate + Nitrate + Crustal + TCM

Use SANDWICH to characterize PM2.5For Data Presention Purposes:

Simplify components of PM2.5 into Sulfate and Nitrate 

the NH

4 and estimated H

2O must be partitione

Carbon can be represented as Total Carbonaceous 

Partition NH4 and 

H20 Combine OCM 

For further data details, See: http://www.epa.gov/a
(a) W. Reduced Nitrates

(b) With added water

SOUnkCrupasTCMNO

(c) Plus passive PM2.5 

(= FRM blank)

(d) Remaining unknis assigned to carb

(1) Approachusing measurementsand calculated values

Conceptual Overview of Mass Balance Appr

*

Distributeunknown(or scale all down) equally

* Default SANDWICH can be modified to consider 

other components, like salt. This reduces estimate of 

(2) SANDWICH

Sulfate mass increases
Uncertainties, Caveats and Data 

• Assumptions:

– Reduced nitrate and enhanced sulfate are more ref

what might be measured by the FRM

– OCM is the most uncertain mass component

• TCM

mb is upper estimate and subject to error

non-C components

• Inclusion of all “known” components is good

– E.g. Salt for coastal areas or urban winterti

• Sometimes, TCMmb can be negative 

– But, so can measurement derived “OC-b”– So, modified SANDWICH uses measurement dat

“OCM floor” (See discussion on Air Explorer)

• TCMmb can be used to ground truth k*(OC-b
Application of SANDWICH to STN Da

and

Some examples of SANDWICH for QC
RCFM SANDWIC

Annual Average Composition (2002-04) in Eas

Less nitrate and more sulfate mass with SANDWI

NA area without STN data (02-0

Black outlined pies have collocate

area area_annual_d

v

NA area: Johnstown, PA 15.3NA area: Martinsburg, WV-Hagerstown, MD 16.1NA area: Parkersburg-Marietta, WV-OH 15.2NA area: Reading, PA 16.1NA area: Steubenville-Weirton, OH-WV 17

NA area: Wheeling, WV-OH 15.1
RCFM SANDWICH

Annual Average Composition (2002-04) in We

Less nitrate and more carbon mass with SANDW

Black outlined pies have collocate
Q1

Q3

Sulfate_mass Nitrate_mass TCM Unknown_at_DV_site Crustal Passive

Quarterly PM2.5 Composition in Eastern NA areas
Seattle-Bellevue-Everett,WA site=530330080 Chicago,IL site=170310076

Riverside-San Bernardino,CA site=060658001

2002 2003 2004 2005

Sulfate_mass Nitrate_mass OCM Crustal

PM2.5 and Components, ug/m3

0 60 0 60 Seattle C

Birm

2002 2003 2

Rubidoux, CA

FRM PM2.5
Chicago,IL site=170310076 Seattle-Bellevue-Everett,WA site=530330080

Birmingham,AL site=010730023

Riverside-San Bernardino,CA site=060658001

Sulfate_mass Nitrate_mass OCMmb Crustal 

Seattle C

Rubidoux, CA

2002 2003 2004 2005

PM2.5 and Components, ug/m3

0 60 0 60 Birm

(Morand O

2002 2003 2

(More OCM)

(Less nitrate, more sulfate mass and OCM)

(More sulfate mamore OCM)
2 3 4 5 6 7 8 9 10 11 12

Riverside-San Bernardino,CA site= 060

2 3 4 5 6 7 8 

PM2.5 and Components, ug/m3

0 60

Rubidoux, CA (2005)

RCFM SANDWICH

FRM PM2.5 mass Less nitrate ma

More sulfate an

Gray line shows {OCMmb - OCM

Chem Sulfate_mass Nitrate_mass 

OCMmb Crustal 

Over-estimates FRM mass
Birmingham,AL site= 010732003 (2005)

0.05.0

 10 15 20 25 30 35 40 45 50 55 60

1 2 3 4 5 6 7 8 9 10 11 12

Gra

y line shows {OCMmb - OC

Chem Sulfate_mass Nitrate_mas

OCMmb Crustal 

1 2 3 4 5 6 7 

RCFM SANDWICH

FRM PM2.5 mass

PM2.5 and Components, ug/m3

0 60 Less nitrate ma

More sulfate an

Birmingham, AL (2005)

Under-estimates FRM mass
How to Use SANDWICH fo

• Comparisons of Constructed Fine Mass w

measured FRM mass

– Using reduced nitrate and hydrated sulfateInstead of CFM=[SO4]+[NO3]+[NH4]+ [TCM14]+[Cr] 

Use CFM=[SO4]+[NO3r]+[NH4]+[H2O] [TCM14]+[C

• Examine TCMmb vs. [k*(OC-b)+EC]

– Negative numbers and large deviations can b

informative.

– Three examples

• Use time series and scatter plots• Preliminary QC findings are presented
Huntington-Ashland,WV-KY-OH Kentucky 210190017 SASS 2005 

PLOT tcm sulfate nitrate

cr tcm14 mf2

PM2.5 and chemical component mass, ug/m3

-10

0

10203040

date

01JAN05 01MAR05 01MAY05 01JUL05 01SEP05 01NO

TCMmb, ug/m3

-10

0

102030405060

tcm14

-10 0 10 20 30 40 50 60

FRM PM2.5=4.3 (Too Low!)SO4=5.9

TCMmb= -6.9 ug/m3 TCM1.4= 3.8 ug/m3

P

SO

Ashland KY, 2002-05TCMmb vs TCM1.4

TCM14=1.
Greenville-Spartanburg-Anderson,SC South Carolina 450450009 SASS 2003 

PLOT tcm sulfate nitrate

cr tcm14 mf2

PM2.5 and chemical component mass, ug/m3

0

1020304050

date

01JAN03 01MAR03 01MAY03 01JUL03 01SEP03 01NO

TCMmb, ug/m3

-10

0

102030405060

tcm14

-10 0 10 20 30 40 50 60

PM2.5 =40.1 ug/m3

TCMmb= 39.2 ug/m

SO4=0.1 ug/m3

Greenville 

2002-05
Seattle-Bellevue-Everett,WA Washington 530330024 RAAS 2002 

PLOT tcm sulfate nitrate

cr tcm14 mf2

PM2.5 and chemical component mass, ug/m3

-10

0

10203040

date

01JAN02 01MAR02 01MAY02 01JUL02 01SEP02 01NO

TCMmb= 25.1TCM1.4= 8.9

Seattle,WA 2002

PM2.5 = 29.1 

(Mar3)

TCMmbTCM1.4

TCMmb, ug/m3

-10

0

102030405060

tcm14

-10 0 10 20 30 

2002-05

TCM14=1.
Seattle-Bellevue-Everett,WA Washington 530330024 RAAS 2004 

PLOT tcm sulfate nitrate

cr tcm14 mf2

PM2.5 and chemical component mass, ug/m3

0

1020304050

date

01JAN04 01MAR04 01MAY04 01JUL04 01SEP04 01NOV0

TCMmbTCM1.4

Seattle,WA 2004

PM2.5

Measurement Program Implications:

TCM can be estimated

from PM2.5, sulfate and nitrate
Seattle-Bellevue-Everett,WA Washington 530330024 RAAS 

PLOT tcm tcm14 TCMplus TCMminus

TCMmb, ug/m3

-10

0

102030405060

tcm14

-10 0 10 20 30 40 50 60

Seattle-Bellevue-Everett,WA Washington 5303300

PLOT tcm tcm14 TCM

TCMmb, ug/m3

-10

0

102030405060

tcm14

-10 0 10 20 30 

Seattle-Bellevue-Everett,WA Washington 530330080 MASS 

PLOT tcm tcm14 TCMplus TCMminus

TCMmb, ug/m3

-10

0

102030405060

tcm14

-10 0 10 20 30 40 50 60

TCMmb vs TCM1.4 for 3 sites in Seattle (20

Site 024 RAAS Site Site 080 MASS MASS sampler appears to re

combination of “k” and “b” to consistency between TCMmHigher “k” =1.8 more consistwoodsmoke aerosol Æ suggests that SASS sampadd’l artifact in proportion to is offset by “k=1.4”)See TCM poster (for further d

TCM14=1.4(OC-0.3)+ECTCM14=1.4(OC-1.3)+EC TCM14=
SANDWICH data are now available on Air 

http://www.epa.gov/airexplorer/

See Mark Schmidt’s Demo, Wednesday 3:30pm
A Few Summary Points

• Adjustments to STN speciation 

measurements are needed to represFRM PM2.5 mass

• SANDWICH estimates composition 

might have been measured by the F

• TCMmb

– helps evaluate C fudge factors (k & b) 

validate C measurements

– Use it to estimate TCM without measu
Questions?

Now or at Tomorrow's Poster Se

I hear they will be serving Frank Sandw
Summary and Next 

Inferred carbon by mass bala• Directly accounts for 

• Adsorbed organic gases and carbo• Volatilized OC and other carbonacartifacts); • Total FRM mass associated with c

• Eliminates need for blank corrections carbon elements associated with measur• Can be used to corroborate measuremComparison of TCMmb with k• The correct combination of “k” and “bdata.

• With STN’s Met One (SASS) and environments, TCMmb generally agrAssuming that k=1.8 would be more higher blank correction (b) would be backup filters behind Teflon might r• For sites with the URG MASS samconsistent with published values. Dablank correction & are more sensitiv

Next Steps• For national consistency in ambient caprotocol to the IMPROVE method. STto be phased in over three years will alsSTN data from SASS and RAAS sampl•EPA has funded DRI to recommend prurban samplers (using backup filters) an

IM W N ot in a M SA site= 550270007 SA SS

PLOT tcm tcm14 tcm

tcm14 tcm14_new tcm14_new ec tcm18_new tcm18_new

tcm

012345

time

2002 2003 2004 2005 2006

Trends in Carbonaceous PM2.5 using Measured STN Carbon and “SANDWI

Neil Frank

Office of Air Quality Planning and Standards, USEPA Research Triangle Park NC 27711

Background

Carbonaceous mass is one of the largest PM2.5 chemical components, but is the most challenging to estimate. The typicalmethod to calculate total carbonaceous mass (TCM) involves correcting measured organic carbon (OC) for positive sampling artifact (blank correction), multiplying the result by a simple factor (e.g. 1.4) to account for oxygen, hydrogen and other elements in ambient carbon compounds and then adding measured EC. Neither of these OC adjustments can be accurately estimated from existing STN measurements or data. The STN program does not currently utilizebackup filters; therefore, field and trip blanks together with sampler flow rate permit at best a crude estimate of the OC artifact. EPA has used a single network wide value derived from 2001-02 STN data. For the multiplier to create OCM, generic values are usually taken from the literature; but in reality vary with the mix of particulate OC compounds and could therefore vary by location, season and even day. To estimate FRM PM2.5 (retained on Teflon with typically higher 

face velocity), different adjustments are probably needed. This poster provides estimates of TCM by material balance with FRM mass and its non-C components. These “SANDWICH” results are compared to measurement derived TCM. Trends in STN blank values are also considered.

Nov 1, 2006 Email: frank.neil@epa.gov

Sources of error in TCM =k*(OC-b)+EC

• Analytical uncertainty• Blank correction to account for positive sampling artifact

• With STN field blanks, no dynamic back up filters.• Differs among urban STN speciation samplers

• Conversion of OC to OC mass (OCM) (+ 33%)

• 1.4 < k < 1.8 ("typical" urban) ref: Turpin (2001)• 2.0 < k < 2.4 ("typical" rural)

• Weighted average needed for mixed urban/regional aerosol

• Turpin's revised estimates based on limited speciation data

• OC- EC split (and unaccounted mass for “EC”)

• Retained carbon mass on FRM Teflon vs STN quartz

• Less volatile OC may be retained on Teflon **• Water [= ~10-24% of PM2.5 water]

** Volatile OC can vary by location and sampling day. Retained particulate OC 

depends on filter face velocity.

"SANDWICH“ ApproachQ Sulfate, Adjusted Nitrate, Derived Water, Inferred Carbonaceous 

mass Hybrid material balance approach

• TCMmb = PM2.5 - { [SO4] + [NO3FRM] +[NH4] +[water] 

+ [Crustal] + [FRM blank]}

• OCMmb = [TCMmb] – [EC]• Water and reduced FRM NO3 are estimated by models.• Other PM2.5 constituents eg. salt, could also be considered• TCMmb explicitly accounts for positive and negative sampling 

artifacts, OC hydration, and mass multipliers for carbonaceous 

material retained on FRM Teflon.

• TCMmb is upper estimate for TCM and is subject to error in non-C 

components.

Reference: Frank, N. Retained Nitrate, Hydrated Sulfates, and Carbonaceous Mass in Federal 

Reference Method Fine Particulate Matter for Six Eastern U.S. Cities, J. Air & Waste Manage. Assoc. 56: 500–511 (2006)

Example Site-Specific TCM 

Monthly Average TCM (TCM

ug C/ filter ug C/m3

MetOne (SASS) 9.6 14.8 1.5Anderson (RAAS) 10.4 13.5 1.3R&P 2300 14.4 16.1 1.1URG (MASS) 24 7.7 0.3

Network Average Total

Carbon on STN Blank Filters* 

24-hr 

sample 

Volume(m3 STN sampler )

*Network-wide values from 2001-02 data as reported by RTI and previously used by EPA to adjust OC

sam pler_type=A nderson RA S S

filter blank, total carbon (expressed as ug/m3)

 0 1 2 3 4 5 6

time

2001 2002 2003 2004 2005 2006

sampler_type=METONE SASS

filter blank, total carbon (expressed as ug/m3)

 0 1 2 3 4 5 6

time

2000 2001 2002 2003 2004 2005 2006

sampler_type=URG MAAS

filter blank, total carbon (expressed as ug/m3)

 0 1 2 3 4 5 6

time

2000 2001 2002 2003 2004 2005 2006

Sampler sites 2001 2002 2003 2004 2005Anderson RASS 22 1.19 1.50 1.03 0.90 0.99

METONE SASS 140 1.53 1.63 1.21 1.01 1.09URG MAAS 5 0.29 0.34 0.25 0.26 0.43

Since 2002, STN field and trip blanks values for SASS and RAAS samplers have decreased 33% and values for MASS samplers have increased 25%. Reasons for the change are not known at this time

Site Specific Differences in STN Field BlanksNo apparent consistent difference in TC field blank values among sites. Most 

site average values for Met-One SASS (2004-5) range from 0.75-1.5 ug/m3 as shown.

. .

tc_conc (ug/m3): <=0.75 >0.75 to 1 >1 to 1.25 >1.25-1.5 >1.5 

. .

tc_conc (ug/m 3): <=0.75 >0.75 to 1 >1 to 1.25 >1.25-1.5 >1.5 

Regional Trends in TCM, 2002-2005

S E

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2002 2003 2004 2005 2006

N E

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2002 2003 2004 2005 2006

IMW

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tim e

2002 2003 2004 2005 2006

Regional average values of TCM agree well with k*(OC-b) using k=1.4 and year specific b values. For some US Regions and sites, the old b values seem better. The successful choice of k to represent retained FRM mass (on Teflon) appears to depend on the selected value for “b”. The value for “k” may also depend on the particular thermal analytical technique and OC-EC split. Distribution of site-quarterly averages of TCM are shown.

Similarly, no apparent pattern was observed among TC field blank values by calendar quarter (preliminary analysis). Due to large within-site and between year variability and few samples, multiyear network-wide values seem reasonable to use.

NE W as hington,D C-

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2002 2003 

IM W Ham ilton-M idd

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2002 2003 

IM W C hicago,IL site= 170310076 M A SS

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tim e

2002 2003 2004 2005 2006

IM W Not in a M SA site= 550270007 SASS

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2002 2003 2004 2005 20

Chicago, ILHigher “k” needed for FRM balance (resulting from local highway work whichstarted in 2004). 

2004 2005

IM W Chicago,IL site= 170310076 M ASS

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2002 2003 2004 2005 2

Local emission increase or underestimate of NO3?

Cincinnati, OH

TCMmb agrees with k=1.4 and 

Mayville, WI

Rural OC needs k > 1.8, esp in 2004

Washington, DC

TCMmb matches trends with k=1

TCM, ug/m3

Is all extra mass really OCM?

TCMmb

TCM1.4(old b)

TCM1.4

(new b)

TCM, ug/m3

Mayville, WIHigher “k” or lower “b” is needed for mass balanceDuring the winter season (woodsmoke?)

Chicago, IL 

EC

TCMmb

TCM1.8(new b)

Average Total Carbon Blank by year, ug/m3

Industrial MidWest, 11 sites Northeast, 10 sites

Southeast, 11 sites

TCMmb

TCM1.4

(old blank)

TCM1.4

(new blank)

TCM1.4

(old b)

Note: Winter differences between TCMmb and TCM1.8could represent unmeasured NO3 by MASS sampling system

TCMmb

TCMmb

Trends in STN TC field blanks