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

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.

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

1. overall aerosol potential2. atmospheric emissions3. presence of other initiating reactants (O3, OH,

NO3, sunlight, acid catalysts)

1. Terpenoid

2. Aromatic

3. Particle Phase Reactions (aldehydes and alcohols)

Leonardo Da Vinvi described 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

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

myrcene

-pinene

-pinene d-limonene

Synthesis of TerpenesFrom CO2

Ruzika, 1953

No mechanism for isoprene storage

While terpenes can stored in resin duct

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

  Yu et al. Hannel et al

-pinene 22-119 36-148

-pinene 16-119 7- 28**

limonene 13- 63 0- 21

3-carene 2- 21 8- 48

camphene 2- 21 5- 35

sabinene   0- 43

isoprene   0-228

Ambient Concentrations of selected terpenes (pptV)

Aerosol concentrations of selected terpenes products (ng m-

3) 1ng m-3 =~0.1pptVYu et al. Kavouras et al, 1998

Pinic acid 0.5 0.4- 85pinonic acid 0.8 9 - 141norpinonic acid 0.1- 38Pinonaldehyde 1.0 0.2- 32hydroxy-pinonaldehydes 0.5 oxo-liminoic acid 0.8Nopinone 133 0.0 - 13

Scheme 3

+

OO.

O

-pinene

O3

O O

OOO.

O

O

O

norpinonic acid

Criegee1

O

OH

O

O

hydroxypinonaldehyde

OO

norpinonaldehyde

o

+ HO 2+OH+CO

+ HCHO + CH 3OH

Criegee2

OH

O

pinonic acid

O

HO-CH 2

hydroxypinonaldehyde

OO

HO-CH 2

hydroxypinonic acid

OH

OH

O

hydroxypinonic acid

O

OH

OH

O

pinic acid

OOH

O

OH

O

OH

norpinic acid

O

pinalic acid

OOHO

O

O=CH

oxo-pinonaldehyde

+ HO 2+OH+CO

+ HCHO

CH2OH

.

.

pinonaldehyde

OO

Mechanisms can often explain the formation of products

Sesquiterpenes (C15H24)

terpenes15%

isoprene53%

SQS19%

others4%

alcohols9%

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

Lifetimes of Sesquiterpenes

  OH NO3 O3

a-Cedrene 2.6 hours 4 min 14 hours

a-copaene 1.9 hours 2 min 2.5 hours

-Caryphyllene 53 min 2 min 2 min

-Humulene 36 min 1 min 2 min

Longifiolene 3.7 hours 49 min 23 days

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

Fluxes computed with and w/o an ozone scrubber (~50 ppb of O3 w/o

O3 scrubber) over Fuentes, et al. 2000)

with

w/o

Caryophylene

Limonene

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

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    

1. Temperature

2. light

3. injury

Factors that influence emissions

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

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

-pinene emissions compared to temp, and CO2 exchange (Mediterranean

Oak, Kesselmeire et al )

temp

CO2 exchange

-pinene

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 -caryophyllene and trans--ocimene

decreased little (-6%) from the non-drought conditions. Hansen and Seufert,(1999).

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 -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 RHn a normalized relative humidity = (%relative humididy-18)/82

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.

Plant damage

Tropical forest 22Grass/shrubs/hot 22savanna 13Tropical rain forest 11Conifers and evergreens

20

Deciduous 7Re-growing woods 7Marsh/swamp/bogs 2Crops/woods-warm 3tundra 0.4desert 1

Global terpene sources (Tg/y)

Aerosol formation from Terpenes

-pinene

Aerosol potential (Odum theory)

Y MK

K MM

K

K Mo

om

om oo

om

om o

1 1

1

2 2

21 1,

,

,

,( ) ( )

0.95 ppm -pinene + 0. 44ppm NOx

O3

NO

NO2

NO2

model

data

Measured particle mass vs. model

reacted -pinene

data

model

particle phase pinonaldehye

model

data

OO

-pinene

Aerosol potential (Odum theory)

Y MK

K MM

K

K Mo

om

om oo

om

om o

1 1

1

2 2

21 1,

,

,

,( ) ( )

  1 2 Kom,1 Kom,2 %Yield (Y)

3-carene 0.057 .0476 0.063 0.0042 2 -11

caryophyllene 1.00 N/A 0.0416 N/A 17-64

-humulene 1.00 N/A 0.0501 N/A 20-67

limonene 0.0239 0.363 0.055 0.0053 6 -23

-pinene 0.038 0.326 0.171 0.0040 2- 8

-pinene 0.113 0.239 0/094 0.0051 4-13

Griffin et al. biogenic aerosol yields

Relative aerosol potential of terpenoids

Andersson-Sköld and Simpson, JGR, 2001

Used a global photochemcial model to estimate the amount of terpenes and other biogenics that are reacted, ROGi.

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

Griffin et al, JGR, 2000

Natural emissions Tg /y anthropogenic Tg /yr

Soil/mineral aerosol

©

1500Industrial

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

Sienfeld and Pandis from from Kiehl, and Rodhe

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.

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

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

Aerosols from Aromatics (Chamber studies)

m-xylene

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

CH3

OH OH

CH2.

O=CH

NO NO2

+O2

CH3

H

OH

H .

CH3OH

*

O2

+ HO2

+ H2O

CH3

H

OH

H

CH3

O

O

+

.

CH3

O

CH3

H

OH

H

.O

NO

NO2

+O2

toluene

o-cresolbenzaldehyde

rearrangementOH

H

O .

H

H

O

H

OH

H

O

H

+ HO2

+O2

CH3H

+

methylglyoxalbutenedial

oxygen bridgeradical

+ HO2

?ring cleavageradical

CHO CHO

OH

CHO

OH

O2N

CH3

O

O

OH

O

CH3

O

O

O

CH3

O

O

O

H

OO

H3C

H

O O

CH3

O

H

O

O

H

CH3

O

O

H

H

O

O

H

H

O

O

O

H

CH3

O

O

H

H

O

O

O

CH3

CH3

O

H

O

H

O

O

HO

O

H3C

OH

OHO

CH3

O

O

HO

H

O

O

OH

H

O

O

OCH3

O

OH

OOH

CH3

O

O

O

CH3

O

OH

OO

OH

OO

OH

CH3OH O

O

H

O

OH

CH3

O

OHO

H

O

H

OHO

CH3

O

H

OH

CH3 H

O

OH

O

H H

O

OH

O

H

CH3

O

O

H

OOH CH3

O

H

O

OH

OOO

OH

CH3H O

O

Aromatic aldehydes

Ring-retaining carbonyls

Ring-opening carbonyls

Ring-opening oxo-carboxylic acids

Ring-opeining hydoxy-carbonyls

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 )

 

HO

CH3

NO2

HOH

OO

H

H

OOH

O

CH3 H

OOH

O

O

H

O

H

OH

CH3

O

O

O

  Predlog 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 i PoLi}

exp iKp = [iCpart]/[iCgas xTSP]

Particle phase reactions

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

• Aldehyde functional groups can react in the aerosol phase through heterogeneous reactions via hydration, 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)

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;

nebulizer

(NH4)2SO4

Solution

aldehydesalcoholsglyoxal

aldehydesalcoholsglyoxal

(NH4)2SO4+H2SO4

Solution

500 liter Teflon bag (Myoseon Jang, UNC)

7.01

3.58

0.00

1.70

0.89

-0.020.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

reaction systems

yie

lds

(%

)

acid seed +decanol+ octanal

non-acid seed+ decanol+ octanal

• 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.

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.

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.