Total Non-Methane Organic Carbon

Christophe Maris, Myeong Chung, Udo Krischke, Richard Meller

and Suzanne Paulson

Department of Atmospheric SciencesUniversity of California at Los Angeles

Funding Provided by • California Air Resources Board • UC Campus-Laboratory

Collaboration • California Space Institute

MotivationThe goal of this work is to 1. Measure total non-

methane organic compounds (TNMOC), and 2. Determine the relationship between TNMOC

and the sum of the speciated volatile organic compounds (VOC’s) measured by standard techniques.

VOC’s are one of the key determinants of air quality and control strategies.

Standard measurement methods are known to detect hydrocarbons and their oxidation products incompletely.

Possible Sources of Excess TNMOC compared to the Sum of

Speciated VOC’s

(Standard VOC Measurement)

Compounds that are lost in the inlet or column (polars, semi-volatiles).

Compounds that are obscured in the GC baseline (hydrocarbons).

Heteroatom compounds that have a reduced response in an FID.

Method1. Trap VOC’s from 2 ambient air samples

simultaneously in a cryogenically cooled trap. Allow CO, CO2, and CH4 to pass through.

2. Desorb both VOC samples.

Speciated VOC’s: analyze directly with DB-1 Column, GC/FID. = Standard Measurement

TNMOC: oxidize CO2, analyze as methane w/ GC/FID. = True total of VOC’s

3. Compare TNMOC with the standard measurement of VOC’s.

Flow Schematic

FCFC

FC

4

Trap 1

2 1

6

5 6 5

1

2 3

4

Oxidation Catalyst

Vent

Sam

ple

6

5

4 3

2

1 Vent

Trap 2Ni

GC/FID

Methanizer

1

2

3 4

5

6 1

2

3 4

5

6 Vent

FCFC

FCFC

He/O2

He

Vacuum

Vacuum

-70oC

625oC

380oC

Pd

Sampling

3

Valve A

Valve B

Valve C

Valve D

Valve E

Valve A,B: Sampling position Valve C,D: Injection position

Valve E: non-oxidation position

of Speciated VOC’s = 450 ppbC

TNMOC = 620 ppbC

Trapping Efficiency

0

100

200

300

400

-150 -130 -110 -90 -70 -50 -30 -10

Trap Temp. (C)

Are

a C

ou

nts

CO2

propylene

1butene

1pentene

1hexene

benzene

toluene

ethylbenzene

m,p xylene

o xylene

Chamber Oxidation of m-Xylene

0

0.5

1

1.5

2

2.5

3

3.5

-20 0 20 40 60 80 100 120

Time (minutes)

Co

nce

ntr

atio

n (

pp

m)

TNMOC

m-xylene

Sum of Speciated VOC's

TNMOC/ of Speciated VOC’s

Location/Date Average Ratio Site Description

Azusa 9-10/97 1.3 ( 0.3) Downwind Site

UCLA 8/99 1.4 ( 0.4) Upwind, Elevated

Burbank 9/99 1.1 ( 0.2) Heavily Source Influenced

UCLA 9-10/00 2.0 ( 0.7) Upwind, Elevated

UCLA 12/00 1.2 ( 0.15) Upwind, Elevated

Weekend/Weekday UCLA 2000Season Day of Week/

Weather

Average TNMOC (ppbC)

Average TNMOC/Sum of Speciated VOC’s

Sept-Oct WeekdaySunny

444 330 1.56 0.41(stdev-mean=0.04)

WeekendSunny

328150 2.03 0.76(stdev-mean=0.1)

WeekdayCloudy

280 127 2.3 0.54(stdev-mean=0.07)

WeekendCloudy

157 58 2.16 0.68(stdev-mean=0.08)

Nov-Dec Weekday 350 150 1.18 0.14(stdev-mean=0.02)

Weekend 175 120 1.26 0.3(stdev-mean=0.05)

Weekend/Weekday UCLA 2000Season Day of

Week/

Weather

Average TNMOC (ppbC)

Average TNMOC/Sum of

Speciated VOC’s

TNMOC-Sum of Sp. VOC’s

(ppbC)

Sept-Oct Weekday

Sunny

444 330 1.56 0.41(stdev-mean=0.04)

142 117

Weekend

Sunny

328150 2.03 0.76(stdev-mean=0.1)

134 50

Weekday

Cloudy

280 127

2.3 0.54(stdev-mean=0.07)

148 55

Weekend

Cloudy

157 58 2.16 0.68(stdev-mean=0.08)

81 45

Nov-Dec Weekday 350 150

1.18 0.14(stdev-mean=0.02)

45 31

Weekend 175 120

1.26 0.3(stdev-mean=0.05)

2722

9/11 9/12 9/13 9/14 9/15 9/16 9/17 9/181.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7 ratio

[O

zon

e](

pp

bV

)

09/11/00-09/17/00

Weekend

Time of Day(M/D)

Ra

tio([

TC

]/[S

P])

0

10

20

30

40

50

60

70

80

90

100

110 o3

9/19 9/20 9/21 9/22 9/23 9/24 9/25 9/26 9/27 9/28 9/291

2

3

4

5

6 ratio

Weekend09/19/00-09/28/00

Time of Day(M/D)

Ra

tio([

TC

]/[S

P])

0

10

20

30

40

50

60

70

80

90

o3

[O

zone](

ppbV

)

10/7 10/8 10/9 10/101.0

1.5

2.0

2.5

3.0

3.5 ratio

10/07/00-10/09/00Weekend

Time of Day(M/D)

Ratio([

TC

]/[S

P])

0

10

20

30

40

50

60

70

80

O3

[O

zone](

ppbV

)

Excess VOC’s and O3 at West LA

9/15/00 Friday

04 08 12 16 20 240.0

0.2

0.4

0.6

0.8

1.009/15/00

Ratio([T

C]/[

SP

])

Con

cent

ratio

ns o

f HC

(ppm

C)

Time of Day

tc sp

1.0

1.5

2.0

2.5

3.0 ratio

00 04 08 12 16 20 24

0

50

100

150

20009/15/00

NO

x, O

zone (

ppbV

)

Time of Day

o3 cno cno2 cnox

1.0

1.5

2.0

2.5

3.0

TN

MO

C/S

um

of S

pe

ciate

d V

OC

's

UCLA Summer, All Data

00:00 04:00 08:00 12:00 16:00 20:00 24:001.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

Ra

tio([

TC

]/[S

P])

Time of Day

Whole data Weekdays Weekends Sunny Day Cloudy Day

Weekday vs. Weekend

00:00 04:00 08:00 12:00 16:00 20:00 24:00

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

TNM

OC

/ o

f Sp

ecia

ted

VO

C's

Time of Day (PST)

Weekdays Weekends

Sunny vs. Cloudy Days

00:00 04:00 08:00 12:00 16:00 20:00 24:001.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0T

NM

OC

/ o

f S

pe

cia

ted

VO

C's

Time of Day (PST)

Sunny Day Cloudy Day

UCLA Winter

00:00 04:00 08:00 12:00 16:00 20:00 24:00

1.0

1.1

1.2

1.3

1.4

1.5

1.6 R

atio

([T

C]/

[SP

])

Time of Day

weekdays weekends

Excess VOC’s vs. VOC

Concentration

0.0 0.2 0.4 0.6 0.8 1.0 1.20

1

2

3

4

5T

NM

OC

/Sum

of S

peci

ated

VO

C's

of Speciated VOC's (ppmC)

UCLA Sept/Oct 2000

0 1 2 30

1

2

3

TN

MO

C/S

of

Sp

ecia

ted

VO

C's

of Speciated VOC's (ppmC)

Burbank 9/99

0.0 0.2 0.4 0.6 0.8 1.00

1

2

3

TN

MO

C/

of S

peci

ated

VO

C's

of Speciated VOC's

Azusa 9-10/97

0 20 40 60 80 1000.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

TN

MO

C/S

um o

f Spe

ciat

ed V

OC

's

Ozone (ppb)

I Linear Fit of Data1_I

-20 -10 0 10 20 30 40 50 60 700.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

TN

MO

C/S

um o

f Spe

ciat

ed V

OC

's

NO2

I

0 50 100 150 200 2500.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

TN

MO

C/S

um o

f Spe

ciat

ed V

OC

's

NO (ppb)

I

0 50 100 150 200 250

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Sum

of S

peci

ated

VO

C's

NO (ppb)

C Linear Fit of Data1_CUCLA Weekday Summer 2000

R=0.5

R=0.3

9/13/00 Wednesday, 9/17/00 Sunday

04:00 08:00 12:00 16:00 20:00 24:00-50

0

50

100

150

200

25009/13/00

Co

nce

ntr

atio

ns(

pp

bV

)

Time of Day

Ozone NO NO2 NOX

0.8

1.0

1.2

1.4

1.6

1.8

2.0 Ratio R

atio

([T

C]/

[SP

])

00:00 04:00 08:00 12:00 16:00 20:00-20

0

20

40

60

80

100

120

14009/17/00

Conce

ntr

atio

ns(

ppbV

)

Time of Day

Ozone NO NO2 NOX

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

Ratio

Conclusions Standard VOC measurement underestimates VOC

level typically by 10-60%, total can be up to 5x higher than the sum of speciated VOC’s.

Ratio of TNMOC/of speciated VOC’s is often inversely related to the VOC and NOx concentrations.

Excess may be associated with photochemical activity, and possibly with mixing from aloft.

Excess varies strongly with location, day of week and meteorology.

Chemical identity and source of excess VOC’s is still to be determined.