Total Non-Methane OrganicCarbon

Christophe Maris, Myeong Chung,Udo Krischke, Richard Meller

and Suzanne PaulsonDepartment of Atmospheric Sciences

University of California at Los Angeles

Total Non-Methane OrganicCarbon

Funding Provided by • California AirResources Board • UC Campus-Laboratory

Collaboration • California Space Institute

Motivation!Goals: 1. Measure total non-methane organic

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

TNMOC and the sum of the speciated volatileorganic compounds (VOC’s) measured bystandard techniques (Gas chromatograph/flame ionization detector).

!VOC’s are one of the key determinants of airquality and control strategies.

!Standard measurement methods are knownto detect hydrocarbons and their oxidationproducts incompletely.

_________________________________________________

Possible Types of ExcessTNMOC Compared to the Sum

of Speciated VOC’s(Standard VOC Measurement)

" Compounds that are lost in the inlet orcolumn (polars, semi-volatiles).

" Compounds that are obscured in the GCbaseline (hydrocarbons).

" Heteroatom compounds that have a reducedresponse in an FID.

Possible Sources of Excess TNMOCCompared to the Sum of Speciated

VOC’s in Ambient Air

" Photochemical oxidation ofhydrocarbons.

" Direct source emissions. These may beeither oxygenates or semi-volatilehydrocarbons.

Method• Trap VOC’s from 2 ambient air samples

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

• Desorb both VOC samples.Speciated VOC’s: analyze directly with DB-1Column, GC/FID. = Standard MeasurementTNMOC: oxidize CO2, analyze as methane w/GC/FID. = Total VOC’s

3. Compare TNMOC with the standardmeasurement of VOC’s.

_________________________________________________

_________________________________________________

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

Flow Schematic_________________________________________________

Trap I Design

Screws

Grooves for thermocouples

D.: 1mm

Groove s for tra p tubingD.: 6.2mm

Liquid nitrogen

30 mm

30 mm

100 mm

20 mm 60 mm

Liquid nitrogen vent

Liquid nitrogen vent

Qua rtz wool plug

Fused silicaBeads

140 mm

O.D.: 6 mmI.D.: 5.3 mm

_________________________________________________

Sum of SpeciatedVOC’s = 450 ppbC

TNMOC = 620 ppbC

Trapping Efficiency vs. Temperature_________________________________________________

-140 -120 -100 -80 -60 -40 -20 0

0

20

40

60

80

100

Tr

appi

ng e

ffici

ency

(%)

Temperature of Trap I (°C)

1-hexene (1) 1-pentene (1) 1-butene (1) propene (1) 1-hexene (2) 1-pentene (2) 1-butene (2) propene (2) ethanol acetaldehyde formaldehyde

0

200

400

600

800

1000

1200

Equ

ival

ent T

rapp

ed C

O2 (

ppbC

)

CO2

_________________________________________________Correction for Light Hydrocarbons

• Hydrocarbons with 4 or 5 carbon atoms trap withefficiencies between 5 and 80% and C2 and C3hydrocarbons only minimally. Acetaldehyde,methanol, ethanol and acetone etc. also elute inthis region, and are collected at 100%.

• Loss of C3 - C5 hydrocarbons was corrected asfollows:

• 20 samples were trapped at –100 °C where 100%of C4 and C5’s trap and 64% of C3’s trap. Thesewere compared to the chromatograms collected at–60 °C immediately before and after.

Light Hydrocarbons

02468

101214161820

mV

(Spa

n=20

)

0 1 2 3 4 5 6 7 8 9 10 11 12Minutes (Span=12)

2.89 3.

89 5.18

7.11

7.45

7.86 9.

10

9.51 9.72 10

.06

10.2

9

10.8

5

11.6

6

02468

101214161820

mV

(Spa

n=20

)

0 1 2 3 4 5 6 7 8 9 10 11 12Minutes (Span=12)

2.88

3.14

3.59

3.94

4.81

5.06

5.19 5.

57

6.32 7.00

7.10

7.44

7.85

8.51 9.

099.

32 9.49 9.71 10

.05

10.2

8

10.8

4

11.5

211

.65

02468

101214161820

mV

(Spa

n=20

)

0 1 2 3 4 5 6 7 8 9 10 11 12Minutes (Span=12)

2.82 3.85 4.

78 5.16

7.09

7.43

7.85 9.09

9.49

9.71 10

.05

10.2

8

10.8

4

11.6

5-60 C

-100 C

-60 C

_________________________________________________

_________________________________________________Correction for Light Hydrocarbons

• C3 concentrations were corrected using theirtrapping efficiencies.

• Peaks eluting between C3 and C5 were normalizedto the sum of spec. VOC’s at –100 °C.

• The result was compared to the –60 °C chrom-atograms, also normalized.

• The difference, equal to the lost C3-C5hydrocarbons at –60 °C, averaged 12.5% of thesum of speciated VOC’s at –60 °C.

• 6.5% was added to account for untrapped C2’s,based on SCOS-97 Azusa data (McCauley, 1999).

_________________________________________________Correction for Light Hydrocarbons

• Because the lost light hydrocarbons are added toboth the TNMOC and the Sum of Speciated VOC's,they have a minor effect on the ratio of the two:

• This correction shifts the average TNMOC/sum ofspeciated VOC’s ratio from 1.37, 1.77 and 1.1 to1.30, 1.65 and 1.1 for UCLA 2000 summer clear,cloudy, and winter.

• A similar peak-by-peak correction for the Azusadata shifted the that average ratio from 1.29 to1.25.

Linearity

0 2000 4000 6000 8000 10000 120000

500

1000

1500

2000

2500

3000

3500

4000

TNMOC Sum of Speciated VOC's

Concentration (ppbC)

Peak

Are

a (A

rbitr

ary

Uni

ts)

_________________________________________________

0 200 400 600 800 10000

200

400

600

VOC Concentration (ppbV)

Peak

Are

a (A

rbitr

ary

Uni

ts)

Acetaldehyde Methanol Acetone Hexane Dibutyl ether Benzene

0.0 0.4 0.8 1.2 1.6 2.0CO2 Sample Volume (L)

Ambient CO2

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)

Con

cent

ratio

n (p

pm)

TNMOC

m-xylene

Sum of Speciated VOC's

_________________________________________________

Oxidation products of this aromatic are not measured by standard GC/FID,but are measured well with the TNMOC channel.

AQMD IntercomparisonTNMOC Instrument

SCAQMD PAMS GC

Sampling Times (PST)

TNMOC (ppmC)

TNMOC corrected for light hydrocarbons

Sampling Times (PST)

Total Speciated VOC’s (ppmC)

10:00 - 11:00 1.4 11:30 - 12:30 1.7 9:00-12:00 1.53 Average 1.55 1.7 11:30 - 12:30* 0.5 13:00 - 14:00 0.9 11:00-14:00 0.63 Average 0.7 0.75 14:30 - 15:30* 1.8 16:00 - 17:00 5.2 14:00-17:00 3.22 Average 3.5 3.8

_________________________________________________

Trapped Ambient CO2_________________________________________________

Period Sample Volume (mL)

n [CO2]* Average± SD (ppbC)

[CO2] min. (ppbC)

[CO2] max. (ppbC)

[TC] Average±SD (ppbC)

[TC] min. (ppbC)

[TC] max. (ppbC)

1140 15 49±14 36 86 Sunny 09/12/00- 10/09/00

570

5

129±8

121

142

329±178 91 835

1140 10 54±8 41 64 Cloudy 09/12/00- 10/09/00

570

8

115±13

84

126

205±120 68 620

1140 11 59±5 50 69 11/30/00- 12/20/00

570

2

126±16

115

137

269±172 35 889

Detection Limits and Uncertainties_________________________________________________

Data Type Detection Limit

Uncertainty

TNMOC channel

35 ppbC ±10 –20 ppbC; ± 8% at concentrations over 200 ppbC, increasing below

Sum of Speciated VOC’s Channel

1 ppbC + 3-5% - 10-30%

Individual VOC’s 10 pptC ± 3-20%, depending on

separation

TNMOC/Sum of Speciated VOC’s Ratio

__ ± 0.05 to ± 0.10 for ratios between 1 and 2, depending on concentration, - 0.1, + 0.5 for ratios above 2

Field Measurements

• Sources• Ambient air

– Azusa– Burbank– UCLA

• Winter• Summer

_________________________________________________

Diesel and Gasoline_______________________________________________

Source TNMOC/Sum of Speciated VOC's

Gasoline Vapor 1.07-1.09

Diesel Fuel Vapor 1.39-1.44

Diesel Exhaust range

1.2 ± 0.2 1.0-1.6

Instrumentation_______________________________________________

Parameter Instrument Sampling Period (min.)

Sample frequency(1/h)

Sample volume /flow rate

TNMOC And VOC’s

This work 10-20 1-2 500-1140 mL@50- 57mL/min1

NO, NO2, and NOx O3

Thermo Environmental Model 42 Dasibi Model 1003-RS

1 1

60 60

100 mL/min 2 L/min

Aerosols Particle Measuring Systems LAS-X

1 60 200 mL/min

Windspeed, direction, Temperature

Davis Instruments Weather Wizard III

1

60 -

9/15/00 Friday

04 08 12 16 20 240.0

0.2

0.4

0.6

0.8

1.009/15/00

TNM

OC

/Sum of Speciated VO

C's

Org

anic

s (p

pmC

)

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

(ppb

V)

Time of Day

o3 cno cno2 cnox

1.0

1.5

2.0

2.5

3.0

TNM

OC

/Sum of Speciated VO

C's

______________________

Field Data Summary_________________________________________________Site Met. TNMOC

(ppbC) Sum of Spec. VOC's (ppbC)

TNMOC/Sum of Speciated VOC's

Burbank Summer Clear 2300 ±250 2070 ± 200 1.11 ± 0.08 range 8/99

740-4000 730-3000 0.8-1.4

UCLA Summer range 8-9/99

Clear 426 ± 65 150-954

314 ± 42 166-622

1.37 ± 0.12 0.8-2.2

UCLA Summer range 9-10/00

Clear 377± 40 108-925

293 ± 31 85-713

1.30 ± 0.04 1.01-2.4

UCLA Summer range 9-10/00

Cloudy 229 ± 29 75-700

145 ± 21 45-529

1.65 ± 0.08 1.10-3.05

UCLA Winter range 11-12/00

Cloudy 317 ± 45 41-1047

295 ± 43 37-977

1.1 ± 0.03 1.0-1.96

Azusa Summer 9-10/1997

Clear 619 ± 37 201-1475

410 ± 26 242-966

1.26 ± 0.04 0.7-2.1

*All uncertainty ranges are 2σmean

Literature “TNMOC”• Other measurements indicate there is a significant additional pool of

VOC’s.• Roberts et al. (1998) measured TNMOC/sum of speciated VOC’s

ratios of 1.16 –1.36 in rural Nova Scotia using a related approach, inreasonable agreement with our results.

• Alastair et al. (2000) used 2-D GC to find hundreds of additionalorganics in the chromatogram baseline, with a T/S ratio of ~1.67 inMelbourne, Australia.

• Because their measurement used a GC column, it may have missedmany compounds that we measure in our TNMOC channel.

• The cause for this discrepancy may be the selection of the speciatedbaseline.

• We set our baseline conservatively (low) to avoid overestimating theT/S ratio. With auto integrations, we get higher T/S ratios.

• Comparing TNMOC measurements to conventional GC data is tricky.

_________________________________________________

VOCs and T/S Ratio and Ozone at Azusa

00:00 04:00 08:00 12:00 16:00 20:00 24:000

200

400

600

800

1000

1200

140009/04/97-09/29/97 Azusa

Con

cent

ratio

n (p

pbC

)

[TNMOC] [Σ of Speciated]

Time of Day

_________________________________________________

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

1.0

1.5

2.0

2.5

3.0 T/S ratio

TNM

OC

/Σof

Spe

ciat

ed V

OC

's

Time of Day

0

20

40

60

80

100

[Ozone]09/04/97-09/29/97 Azusa

Ozo

ne (p

pbV)

VOCs and TNMOC/Sum ofSpeciated VOC’s at Burbank

_________________________________________________

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

BurbankAverage of [TC](ppmC) = 2.27 +/- 0.65Average of [ ΣSP](ppmC) = 2.06 +/- 0.51

TNMOC

Time(hour)

0

1

2

3

4

5

0

1

2

3

4

5

Con

cent

ratio

ns(p

pmC

)

ΣSP

00:00 04:00 08:00 12:00 16:00 20:00 24:000.6

0.8

1.0

1.2

1.4

1.6 Burbank(09/15/99-10/12/99)

[TN

MO

C]/[Σo

f Spe

ciat

ed V

OC

's]

Time of Day

UCLA Clear vs. Cloudy

Met. No. of Obser-vations

TNMOC (ppbC)

Sum of Spec. VOC's (ppbC)

T/S ratio

Avg. O3 (ppbV)

Avg.MaximumO3 (ppbV)

Clear 100 Average2σmean range

377 40 108-925

293 31 85-713

1.30 0.04 1.01-2.4

36 σ = 22

75 σ =16 45-100

Cloudy 90 Average2σmean range

229 25 75-700

145 17 45-529

1.65 0.08 1.1-3.05

42 σ = 17

61 σ = 13 41-79

____________________________________________

00:00 04:00 08:00 12:00 16:00 20:00 24:000

45

90

135

180

225

270

315

360

Win

d D

irect

ion

(Deg

rees

)

Time of Day (PST)

00:00 04:00 08:00 12:00 16:00 20:00 24:000

45

90

135

180

225

270

315

360

Win

d D

irect

ion

Time (PST)

UCLA Wind DirectionSummer

Winter405 fwy

405 fwyHills

Hills

_________________________________________________

8 10 12 14 16 18 20 220

400

800

1200

1600

2000

128

801

1088 11541259

15161678

1885

1215

789946

10401183

13691508

Hei

ght (

m)

Temperature(°C)

0928

Atmospheric Temperature StructureSummer

____________________________________________

18 20 22 24 26 28 30 320

400

800

1200

1600

2000

128253

780

9841132

1527

1946

128305

610774

914

1219

1521

Hei

ght (

m)

Temperature(°C)

0912 5:00 AM 5:00 PM

Clear Cloudy

Early morning inversion, daytimeshallow mixed layer

Deeper mixed layer, littlediurnal temperature variation

UCLA Clear and Cloudy VOCConcentrations

00:00 04:00 08:00 12:00 16:00 20:00 24:000

200

400

600

800

1000

1200

1400 [TNMOC] [Sum of Speciated]

Con

cent

ratio

n (p

pbC

)

Time of Day

UCLA Clear09/12/00-10/08/00

_________________________________________________

00:00 04:00 08:00 12:00 16:00 20:00 24:000

200

400

600

800

1000

1200

1400 [TNMOC] [Sum of Speciated]

Con

cent

ratio

n (p

pbC

)

UCLA Cloudy

09/12/00-10/08/00

Time of Day

TNMOC/Sum of SpeciatedVOC’s UCLA Clear and Cloudy

_________________________________________________

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

1.0

1.5

2.0

2.5

UCLA Clear09/12/00-10/08/00 T/S ratio

Time of Day

Ozo

ne (p

pbV)

TNM

OC

/Σof

Spe

ciat

ed V

OC

's

0

20

40

60

80

100

[Ozone]

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

1.0

1.5

2.0

2.5

UCLA Cloudy09/12/00-10/08/00

Ozo

ne (p

pbV)

Time of Day

T/S ratio

TNM

OC

/Σof

Spe

ciat

ed V

OC

's

0

20

40

60

80

100

[Ozone]

0 2 4 6 8 10 12 14 16 18 200

400

800

1200

1600

2000

128149 215308

679794

1193

1484

128164

814940

1261

1508

18731974

Hei

ght (

m)

Temperature(°C)

1213

5:00 AM 5:00 PM

Atmospheric Temperature StructureWinter

____________________________________________

VOCs and T/S Ratio at UCLA-Winter_________________________________________________

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

1.0

1.5

2.0

2.5

Ozo

ne (p

pbV)

Time of Day

T/S ratio

TNM

OC

/Σof

Spe

ciat

ed V

OC

's

0

20

40

60

80

10011/30/00-12/20/00 UCLA [Ozone]

00:00 04:00 08:00 12:00 16:00 20:00 24:000

200

400

600

800

1000

1200

1400

1600

Con

cent

ratio

n (p

pbC

)

11/30/00-12/20/00 UCLA

[TNMOC] [Σ of Speciated]

Time of Day

Correlations

TNMOC/Sum of Speciated VOC’s is notcorrelated with:

• O3

• relative humidity• wind speed or direction• or for the most part time of day or day of

week (“weekend effect”).• Weakly correlated with VOC concentration

_________________________________________________

0 40 80 120 1601.0

1.5

2.0

2.5

TNM

OC

/Sum

of S

peci

ated

VO

C's

NO (ppb)

0 40 80 120 1601.0

1.5

2.0

2.5

3.0

TNM

OC

/Sum

of S

peci

ated

VO

C's

NO (ppb)

TNMOC/Sum of Speciated VOC’s and NO_________________________________________________

Sunny

Cloudy

High TNMOC/sum of speciatedVOC’s are associated with lowNO concentrations.

Relationship Between VOCLoading and T/S Ratio

_________________________________________________

0 100 200 300 400 500 6000

100

200

300

400

500

600

700

800

900

TNM

OC

(ppb

C)

Sum of Speciated VOC's (ppbC)

13 + 1.29xR2= 0.91 Clear

0 100 200 300 400 5000

100

200

300

400

500

600

700

TNM

OC

(ppb

C)

Sum of Speciated VOC's (ppbC)

41+1.35xR2= 0.85 Cloudy

T/S Ratio and Ozone_________________________________________________

10 15 20 25 30 35

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

TNM

OC

/Sum

Sp.

VO

C's

Ozone (ppbV)

5:00-8:00 AM R2= 0.38

Site R2 for Correlation with Ozone

Azusa 1997 N/C UCLA Summer 1999 0.19 Burbank Summer 1999 N/C, Negative trendUCLA Summer 2000 Clear

0.11

UCLA Summer 2000 Cloudy

N/C

UCLA Winter N/C Negative trend UCLA Summer 5:00-8:00AM

0.38

Photochemical Processing:Estimating Photochemical Age

-Pairs of aromatics with different lifetimes can beused as markers of photochemical processing.

-The best are aromatics that are emitted in constantratios regardless of source.

-m,p-Xylene and ethylbenzene are typicallycorrelated with R2 < 0.95.

_________________________________________________

Compound KOH Lifetime (hrs)

Benzene 1.23 75 Toluene 5.96 15 Ethylbenzene 7.1 13 m-Xylene 23.6 4 p-Xylene 14.3 6.5 o-Xylene 13.7 6.8

Air Mass Age_________________________________________________

00:00 04:00 08:00 12:00 16:00 20:00 24:001.5

2.0

2.5

3.0

3.5

4.0

4.5

Ratio

of m

,p,X

ylen

e/Et

hylb

enze

ne

Time of Day

09/12/00-10/08/00 UCLA

Sunny Days Cloudy Days

04:00 08:00 12:00 16:00 20:00 24:000.8

1.0

1.2

1.4

1.6

Res

iden

ce ti

me

(hou

r)

UCLA(8/18/99-9/08/99)

ln([m,p-Xylene]/[Ethylbenzene]) ln([m,p-Xylene]/[Ethylbenzene]) = ln(3.7)

ln(m

,p,X

ylen

e/Et

hylb

enze

ne)

Time of Day

04:00 08:00 12:00 16:00 20:00 24:00-1

0

1

2

3

0

0.4

0.8

1.2

1.6

0 6 12 18 24Hour of day

Aromatics indicate maximumaverage photochemicalprocessing times of 2-4hours.Azusa

T/S Ratio and PhotochemicalProcessing

• Assume:– Average speciated mixture of 100 hydrocarbons

from the EPA for 29 cities at 6-9 AM survey(Jeffries 1995).

– Rate constants for each hydrocarbon reacting withOH, and for alkenes with ozone (Atkinson, 1997).

– 0.1 ppt OH (2.5 × 106 molec cm3) and 50 ppbv O3for 4 hours.

-

_________________________________________________

)])[][(exp( 330 tOkOHkAA OOH +−=

T/S Ratio and PhotochemicalProcessing, continued

• Then:– 30% of the hydrocarbons react once with either OH or

ozone.– The organics have an average of 7 carbons, and add

~1.5 functional groups (alcohol, carbonyl, or nitrate) perreaction.

– The total mix increases its heteroatom content relativeto the carbon content by about 7%.

– The effect of this increase on the T/S ratio cannot becalculated precisely; heteroatoms either reduce the FIDresponse or cause the compound to be lost orbroadened in the column.

– The T/S ratio should have little dependence on the timeof day or ozone.

_________________________________________________

UCLA Aromatic Correlations

0.0 0.2 0.4 0.6 0.8 1.0 1.2-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

Y = -0.87-2.08*xR2 = 0.40

09/12/00-10/08/00 Clear Cloudy

ln([TNMOC]/[Sum of Speciated VOC])

ln([E

thyl

benz

ene]

/[Ben

zene

])

_________________________________________________

Compound KOH Lifetime

(hrs) Benzene 1.23 75 Toluene 5.96 15 Ethylbenzene 7.1 13 m-Xylene 23.6 4 p-Xylene 14.3 6.5 o-Xylene 13.7 6.8

Period UCLA2000 Aromatic Ratio R2 w/

self R2 w/ O3

R2 w/ T/S

ln(Ethylbenzene/Benzene) 0.48 0.13 0.40 ln(Toluene/Benzene) 0.46 0.19 0.36 ln(o-Xylene/Benzene) 0.48 0.23 0.34 ln(m,p-Xylene/ Ethylbenzene)

0.99 0.49 0.03

Contribution of Light Oxygenates: Azusa_________________________________________________

Oxygenate AverageConcentra-tion (ppbC)

PercentofTNMOC

FID ResponseFactor (RF = 1per C in NMHC’s)

Acetaldehyde 8.4 1.8 1.65

Methanol 6 1.3 0.77

Ethanol 11 2.4 1.02

Sum 25 5.5

TNMOC meas.in Spec.channel (%)

3.7

Light Oxygenates at UCLA_________________________________________________

1.0 1.5 2.0 2.5 3.0 3.5 4.00

5

10

15

20

25

30

35

Y=26.22 - 1.75*xR2= 0.03

Y=1.64 +6.91*xR2= 0.23

% of Aromatics % of Oxygenates09/12/00-10/08/00

% o

f Aro

mat

ics

& O

xyge

nate

s

TNMOC/Sum of Speciated VOC

0 10 20 30 40 50 60 70 80 900

5

10

15

20

25

30

35

Y =28.67 -0.13*xR2=0.46

Y = 4.98 + 0.18*xR2 = 0.42

09/12/00-10/08/00

% o

f Aro

mat

ics

& O

xygn

ates

[Ozone](ppbV)

% of Aromatics % of Oxygenates

Average propanal + acetonewould result in a T/S ratio of~1.08; observed ratio is 1.45for clear and cloudycombined.

Conclusions" Standard VOC measurement underestimates VOC

level typically by 10-60%, total can be up to 3x higherthan the sum of speciated VOC’s.

" Excess varies strongly with location, day of week andmeteorology.

" At UCLA, large excess TNMOC is stronglyassociated with either high mixing heights (summer)or strong nighttime inversions coupled with lessinfluence from sources.

" Reduced FID response of oxygenates does notaccount for much of the excess organics.

" Excess organics appear to be associated withphotochemical activity and with mixing from aloft.

" Chemical identity and source of excess VOC’s is stillto be determined.

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AcknowledgementsAt CARB: Bart Croes, Drs. Eileen McCauley,

Leo Zafonte, Randy Pasek, Alberto Ayalaand Dongmin Luo

At SCAQMD Steve Barbosa and Phil O’Belland Rudy Eden

At UCLA, Drs. Jill Fenske and Alam Hassonand Andy Ho, Grazyna Orzechowska andEric Ernstner

At NCAR, Rich Leub

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