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What are the precursor compounds for secondary organic aerosols? What are the types of vegetation, vehicle exhaust, and burning that emit these precursors and under what conditions? R.Kamens, M. Jang, S. Lee, M. Jaoui, Depart. of Environ. Sci. and Eng. UNC-Chapel Hill kamens@unc.edu.

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slide1

What are the precursor compounds for secondary organic aerosols? What are the types of vegetation, vehicle exhaust, and burning that emit these precursors and under what conditions?

R.Kamens, M. Jang, S. Lee, M. Jaoui, Depart. of Environ. Sci. and Eng.UNC-Chapel Hill

kamens@unc.edu

slide2

Secondary organic aerosol (SOA) material may be defined as organic compounds that reside in the aerosol phase as a function of atmospheric reactions that occur in either the gas or particle phases.

slide3

The relative importance of precursors to secondary aerosol formation will depend on:

  • overall aerosol potential
  • atmospheric emissions
  • presence of other initiating reactants (O3, OH, NO3, sunlight, acid catalysts)
slide4

1. Terpenoid

2. Aromatic

3. Particle Phase Reactions

(aldehydes and alcohols)

slide5

Leonardo Da Vinvidescribed blue haze and thought that plant emissions were its source…(Went, 1959)

Da Vinvi believed that it was due to water moisture emitted from the plants

slide6

F.W.Went published papers on biogenic emissions from vegetation over 40 years ago.

He posed the question, “what happens to 17.5x107 tons of terpene-like hydrocarbons or slightly oxygenated hydrocarbons once they are in the atmosphere?”

Went suggested that terpenes are removed from the atmosphere by reaction with ozone and demonstrated “blue haze” formation by adding crushed pine or fir needles to a jar with dilute ozone.

different terpene structures
Different Terpene structures

a-pinene

b-pinene

myrcene

d-limonene

slide8

Synthesis of Terpenes

From CO2

Ruzika, 1953

No mechanism for isoprene storage

While terpenes can stored in resin duct

slide9

Global VOC Emissions Rates Estimates: Guenther et al, 1995 (Tg/y)

Isoprene Monoterpenes ORVOC Total VOC

Woods 372 95 177 821

Crops 34 6 45 120

Shrub 103 25 33 194

Ocean 0 0 2.5 5

Other 4 1 2 9

All 503 127 260 1150

slide10

Yu et al.

Hannel et al

a-pinene

22-119

36-148

b-pinene

16-119

7- 28**

limonene

13- 63

0- 21

D3-carene

2- 21

8- 48

camphene

2- 21

5- 35

sabinene

0- 43

isoprene

0-228

Ambient Concentrations of selected terpenes (pptV)

slide11

Aerosol concentrations of selected terpenes products (ng m-3)

1ng m-3 =~0.1pptV

Yu et al.Kavouras et al, 1998

Pinic acid 0.5 0.4- 85

pinonic acid 0.8 9 - 141

norpinonic acid 0.1- 38

Pinonaldehyde 1.0 0.2- 32

hydroxy-pinonaldehydes 0.5

oxo-liminoic acid 0.8

Nopinone 133 0.0 - 13

slide14

Sesquiterpenes (C15H24)

There is a dearth of data on the emissions strength of sesquesterpenes compared to terpenes

May contribute as much as 9% to the total biogenic emissions from plants. (Helmig ,et al, 1994)

Flux data, Atlanta forest, Helmig et al., 1999

slide15

OH

NO3

O3

a-Cedrene

2.6 hours

4 min

14 hours

a-copaene

1.9 hours

2 min

2.5 hours

b-Caryphyllene

53 min

2 min

2 min

a-Humulene

36 min

1 min

2 min

Longifiolene

3.7 hours

49 min

23 days

Lifetimes of Sesquiterpenes

average OH concentration =1.6x106; NO3 = 5x108 for 12 hours of night time; O3= 7x1011 (molecules cm-3)

slide16

Limonene

Fluxes computed with and w/o an ozone scrubber (~50 ppb of O3 w/o O3 scrubber) over Fuentes, et al. 2000)

Caryophylene

with

w/o

slide17

alcohols

ketones

alkanes

p-cymen-8-ol*

2-heptanone

n-hexane and C10-C17

cis-3-hexen-1-ol

2-methyl-6-methylene-1-7-octadien-3-one*

Aromatics

p-cymene

linalool

pinacarvone*

alkenes

acetates

verbenone*

1-decene

bornylacetate

ethers

1-dodecene

butylacetate*

1-,8 cinole

1-hexadecene*

cis-3-hexenylacetate

p-dimethylhydroxy benzene

p-mentha-1,2,8-triene*

aldehydes

esters

1-pentadecene*

n-hexanal

methylsalicyclate*

1-tetradecene

trans-2-hexenal

Other emissions (Winer et al. , Kesselmeier and Staudt )

slide18

Factors that influence emissions

1. Temperature

2. light

3. injury

b pinene emission rates per gram of dry biomass as a function of temperature fuentes et al 2000
b-pinene emission rates per gram of dry biomass as a function of temperature (Fuentes, et al. 2000)

E = Es exp {b (T-Ts)} Tingy et al.

a pinene emissions compared to temp and co 2 exchange mediterranean oak kesselmeire et al
a-pinene emissions compared to temp, and CO2 exchange (Mediterranean Oak,Kesselmeire et al )

a-pinene

temp

CO2 exchange

slide21

Changes in relative humidity were generally not deemed to be an important factor affecting terpene emissions (Guenther, JGR,1991)A young orange tree was exposed to drought stress by withholding water. Emissions of b-caryophyllene and trans-b-ocimene decreased little (-6%) from the non-drought conditions. Hansen and Seufert,(1999).

slide22

Emissions from drought-stressed apple leaves seem to show significant increases in hexanal, 2-hexenal, and hexanol (Ebel et al. 1995)Shade,et al (G. Res. Let.,1999) measured increases in monoterpene emissions of D-3 carene over a ponderosa pine plantation in the Sierra Nevada mountains after rain events and under high humidity, Tingey equation is corrected by multiplying by a relative humidity factor, BET.BET= cxRHn)/((1-cRHn)x(1+(c-1)xRHn) where c a constant, and RHna normalized relative humidity = (%relative humididy-18)/82

slide23

Plant damage

Emissions from damaged leaves contain C6-aldehydes and alcohols.Temporary increases in terpene emissions have been observed from mounting plants in chambers.Isoprene emissions seem unaffected by plant damage. Injury to the bark of pine trees increases terpene emissions. Fungal attack on lodgepole pines releases terpenes and high amounts of ethanol, thought to attract pine beetles.

slide29

Measured particle mass vs. model

reacted a-pinene

data

model

slide30

O

O

particle phase pinonaldehye

data

model

slide32

a1

a2

Kom,1

Kom,2

%Yield (Y)

D3-carene

0.057

.0476

0.063

0.0042

2 -11

caryophyllene

1.00

N/A

0.0416

N/A

17-64

a-humulene

1.00

N/A

0.0501

N/A

20-67

limonene

0.0239

0.363

0.055

0.0053

6 -23

a-pinene

0.038

0.326

0.171

0.0040

2- 8

b-pinene

0.113

0.239

0/094

0.0051

4-13

Griffin et al. biogenic aerosol yields

slide33

Relative aerosol potential of terpenoids

Andersson-Sköld and Simpson, JGR, 2001

slide34

Griffin et al, JGR, 2000

Used a global photochemcial model to estimate the amount of terpenes and other biogenics that are reacted, DROGi.These were used in conjunction with specific compound “Odum fitting” constants to estimate total boigenic aerosol production on a yearly basis.This may be a conservative estimate because the fitting contents are derived at 308K, does not consider other aerosol surfaces, or particle phase reactions

slide35

Sienfeld and Pandis from from Kiehl, and Rodhe

Natural emissions

Tg /y

anthropogenic

Tg /yr

Soil/mineral aerosol ©

1500

Industrial dust ©

100

Sea salt ©

1300

Soot

10

Volcanic dust ©

30

Sulfate from SO2

190

biological debris

©

50

Biomass burning

90

Sulfates from biological gases

130

Nitrates from NOx

50

Volcanic Sulfates

20

VOCs

10

Nitrates

60

Biogenic aerosols

13-24

Total

3100

Total

450

slide36

Aromatics

Globally, about 25 Tg/yr of toluene and benzene and are emitted with fossil fuels contributing ~80%, and biomass burning another 20 % (Ehhalt, 1999)

A reasonable total aromatic emission rate might be 3 times the toluene+benzene emission rate.

slide37

Aromatics

Volatile aromatic compounds comprise up to 45% in urban of the VOCs US and European locations.

At rural sites it is 1-2%

Toluene, m-and p-xylenes, benzene, 1,2,4-trimethyl benzene, o-xylene and ethylbenzene make up 60-75% of this load

slide38

Aromatics

Tunnel studies show that aromatic emissions comprise 40-48% of the total nonmethane hydrocarbon emissions for LD and HD vehicles (Sagebiel, and Zielinska et al.)

On a per mile basis heavy duty trucks emit more than twice the aromatic mass that light duty vehicles emit

The same aromatics as found in ambient air, comprise 60% of the LD aromatic emissions and 27% of the HD

slide39

Aerosols from Aromatics (Chamber studies)

1. Odum et al.

2. Izumi et al.

3. Holes, et al.

4. Kliendienst et al.

5. Forstner et al.

6. Hurley et al

7. Jang and

Kamens

m-xylene

slide42

Particle phase reactions

In UNC chamber experiments partitioning “Pankow” coefficients for aldehydes are much higher than predicted partitioning coefficients, calculated from the vapor pressures and activity coefficients (Jang and Kamens, ES&T, 2001, Kamens and Jaoui, ES&T, 2001 )

slide43

Pred

log iKp

Exp.

log iKp

4.25

-3.8

5.64

-5.69

5.41

-3.86

6.10

-2.66

5.56

-3.23

5.38

-3.91

Toluene gas phase reaction reactions

iKp i= 760 RTx10-6 fom /{Mw gi PoLi}

exp iKp = [iCpart]/[iCgas xTSP]

slide44

Particle phase reactions

Ziemann and Tobias have reported the formation of hemiacetals in the particle phase of secondary organic aerosols

slide45

Aldehyde functional groups can react in the aerosol phase through heterogeneous reactions viahydration, polymerization, and hemiacetal/acetal formation with alcohols.

  • Aldehyde reactions can be radically accelerated by acid catalysts such as particle sulfuric acid (Jang and Kamens, ES&T, 2001)
slide46

Why don’t we see these large highly oxygenated compounds??

Reverse reactions to the original aldehyde parent structures can occur during sample work up/solvent extraction procedures;

slide47

nebulizer

(NH4)2SO4

Solution

(NH4)2SO4+H2SO4

Solution

aldehydes

alcohols

glyoxal

aldehydes

alcohols

glyoxal

500 liter Teflon bag (Myoseon Jang, UNC)

slide48

acid seed +

decanol+ octanal

non-acid seed

+ decanol+ octanal

slide49
To demonstrate the acid catalyzed aldehyde reaction, octanal was reacted directly on a ZnSe FTIR window by adding small amounts of aqueous H2SO4 acid catalyst solution (0.005 M). The spectra of the octanal/acid-catalyst system changed progressively as a function of time
  • The aldehydic C-H stretching at 2715 cm-1 immediately disappeared, the C=O stretching band at 1726 cm-1 gradually decreased
  • and the OH stretching at 3100-3600 cm-1 increased as hydrates formed.
slide50

Future research areas.

  • Determine the importance of particle phase reactions as a source of SOA.
  • Determine the importance of sesquiterpenes in SOA formation.
  • Clarification of the impact of drought and relative humidity on biogenic emissions is needed so these factors can be incorporated into emission models.
slide51

Future research areas (cont.)

  • Integrated chemical mechanisms for predicting SOA from biogenics and aromatic precursors.
  • New analytical techniques to detect and quantify particle phase reactions. These need to be non-invasive or “chemically soft” so that complex particle phase reactions products are not decomposed.