Approach for Substituting Mingo 

IMPROVE Carbon Data

Inter-RPO Data 

Analysis/Monitoring Workgroup

Chuck McDade & Warren White

UC Davis, 9/28/05
What periods and modules 

exhibited compromised data at 

Mingo?

• Mid 2002 through 4/13/05 (end will be 

confirmed after we have received 

April/May 2005 data)

• Apparently affects C module only (carbon), 

due to inlet blockage
Mingo Organic Carbon (OC)

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O

C 24h average, ng/m3 Mingo organic carbon concentrations began diminishing during the third 

quarter of 2002 and remained low throughout the period of reported data.

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1/1/00 1/1/01 1/1/02 1/1/03 1/1/04

O

C 24h average, ng/m3
What data analysis approach might 

compensate for lost data?

• We propose extrapolating from measured years 

to lost years, using the hydrogen measurement 

from the A module to estimate carbon.

• The A module (mass and elements) was visibly 

clogged with mud, but the data through the 

period do not exhibit abnormalities. We 

consider the A module data to be valid.
Determining Organic Mass from 

Hydrogen

• We routinely estimate organics from hydrogen as one of 

our QC checks.

• We assume that:

– All sulfur is fully neutralized

– Hydrogen associated with nitrates and water volatilizes in 

vacuum during the hydrogen analysis

• We subtract 0.25*S from hydrogen, because 0.25 is the 

mass ratio of H to S in ammonium sulfate
Mingo SO4/S

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S

O

4/S

R

atio

Using hydrogen to substitute for carbon requires subtracting out the 

hydrogen associated with sulfur. 2001 is a good choice for a baseline 

period because the SO4/S ratio is relatively stable and is similar in 

behavior to the period after mid-2002, when we will be substituting. This 

plot also demonstrates that the A module did not suffer inlet blockage.

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1

2

1/1/00 1/1/01 1/1/02 1/1/03 1/1/04

S

O

4/S

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atio
Mingo OC vs. org_H, 2001 data only

y = 8.0247x

R

2

 = 0.7935

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O

C, ng/m3

During 2001, the ratio of OC to hydrogen associated with organics 

(org_H) is around 8. org_H equals measured hydrogen minus 0.25*S, 

where 0.25 is the mass ratio of H to S in ammonium sulfate. So, we can 

use 8*org_H as a surrogate for OC; we will call the surrogate OCH.

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org_H, ng/m3
Mingo Measured OC & Surrogate OCH from Hydrogen

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h

a

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era

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e, n

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OCH mimics OC quite well up until mid-2002. OCH even succeeds in 

identifying the high concentration spikes in 2000 and 2001. OCH failed 

with negative values in July 2002 when the SO4/S ratio was not well 

controlled (see slide 6), but seems reasonable during other periods.

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OC OCH
Mingo OCH/OC Ratio

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O

C

H/O

C

Ratio

The OCH/OC ratio began to increase from 1 during August 2002, 

suggesting that inlet blockage began during that month. We propose that 

substitution of OCH for OC begin in August 2002.

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-1

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1/1/00 1/1/01 1/1/02 1/1/03 1/1/04
Mingo OC and Substituted OCH beginning 8/1/02

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This plot illustrates the data record that we recommend for organic 

carbon, with measured OC used through July 2002 and OCH substituted 

beginning in August 2002.

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1/1/00 1/1/01 1/1/02 1/1/03 1/1/04

OC OCH
Mingo EC/OC Ratio

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0.7

E

C/O

C

Ratio

Now we need to identify a substitute for elemental carbon (EC), which is 

also compromised by the inlet blockage. We can estimate the EC/OC 

ratio using measured data for the period that we consider valid, from 2000 

through July 2002.

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0.2

1/1/00 1/1/01 1/1/02 1/1/03 1/1/04
Mingo EC vs. OC, data through 7/02 only

y = 0.1921x

R

2

 = 0.7101

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E

C, ng/m3

The EC/OC ratio through July 2002 is around 0.2. We get this same ratio 

if we use all data, through 2004.

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OC, ng/m3
Mingo Measured EC & Surrogate 0.2xOCH from Hydrogen

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Here we take the next step and substitute 0.2*OCH for EC. As with OC, 

our substitution mimics EC quite well up until mid-2002, and even 

succeeds in identifying the high concentration spikes in 2000 and 2001. 

Again, we recommend substituting beginning in August 2002.

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1/1/00 1/1/01 1/1/02 1/1/03 1/1/04
RMS 

Precision

OC EC

Reported data vs. substituted data, 2001 21% 24%

One measure of the reliability of the substituted data is to compare its 

agreement with measured data (when both are available in 2001) against 

the precision determined from identical collocated samplers. The 

variability among reported versus substituted data is only slightly greater 

than that among identical collocated samplers.

Collocated IMPROVE samplers 13% 22%
Mingo EC & Substituted 0.2xOCH beginning 8/1/02

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This plot illustrates the data record that we recommend for elemental 

carbon, with measured EC used through July 2002 and 0.2*OCH 

substituted beginning in August 2002.

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500

1/1/00 1/1/01 1/1/02 1/1/03 1/1/04

EC OCHx0.2
What caused the decrease in 

carbon concentrations?

• Blocked inlets were discovered at 

Swanquarter, NC, in March 2005, caked 

with mud from insects.

• Other sites were inspected, and blocked 

inlets were found at Mingo, replaced on 

4/13/05.

• Blocked inlets were returned to UC Davis 

for inspection and testing.
Blocked Inlet, Swanquarter, NC
Inlet Tests at UC Davis

• Extremely blocked inlets (98 to 100% blocked) 

were compared against clean inlets and less 

blocked inlets in side-by-side tests in Davis.

• Tests revealed that an inlet must be >98% 

blocked (by visual inspection) to affect fine mass 

significantly.

• The Mingo A Module inlet showed substantial 

blockage in these tests, yet the 2002-2004 A 

module data do not appear to be unusual.
Inlet Tests at UC Davis

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a

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(

g

/

m

3

)

98-100%

clogged

85-95 % clogged

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1.0

1.5

MINGA

MINGC

SWANA

MINGB

SWANB

SIKEB

HEGLC

CleanCleanCleanCleanClean

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(
Why didn’t we see the problem 

earlier?

• UCD’s historical data quality assurance 

approach examined each quarter of data 

separately. Subtle changes over time were not 

evident.

• New approach supplements existing checks by 

examining time series of concentrations and 

comparing current levels against those observed 

in prior years.

• Flowrates were normal; Mingo did not fail any of 

our standard quantitative tests.
Old Approach: Time Series

Sulfur

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Σ S3 Σ SO4r

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12/2 12/14 12/26 1/7 1/19 1/31 2/12 2/24
Sulfur

y = 1.03x - 173.31

R2 = 0.92

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Old Approach: Regression

y = 0.95x

R2 = 0.92

y = 1.04x - 190.90

R

2

 = 0.97

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S3

S

O4

=
New Approach:

Long-Term Time Series
How can we prevent recurrences?

• New inlet design, easier to clean and less 

likely to clog.

• Disassembly and cleaning at annual 

maintenance.

• Weekly inspection by site operators.

• Awareness of the problem when 

encountering unusual data.
New Style Inlet