Gas/particle partitioning of primary Gas/particle partitioning of primary and secondary organic aerosol and secondary organic aerosol

products in a boreal forestproducts in a boreal forest

Euripides G. Stephanou, Maria Apostolaki and Manolis Tsapakis

Environmental Chemical Processes Laboratory (ECPL)Department of Chemistry

School of Sciences and Engineering University of Crete

Biogenic Organic AerosolBiogenic Organic Aerosol

Temp. Wind Epicuticular Epicuticular waxeswaxes

MonoterpenesMonoterpenes

Low-vapor pressureLow-vapor pressuremulti-functional compoundsmulti-functional compounds

OH O3 NO3

0.01 0.1 1 100.001Diameter (Diameter (μμm)m)

???

Gas phase Particle phase

Pankow’s (1994) model of gas/particle partitioning of semi-volatile organic compounds in an amorphous organic particle:

omMW910

omfTR7.501

logiom,

logγoL

logpip,

logK

Kp,i: partitioning coefficient of the i-compound (in m3 μg-1) between the two phases Po

L: vapor pressure (torr) of the subcooled compound i om,i : activity coefficient of the compound i in the aerosol mixture R: constant of ideal gases (8.314 J mol-1 K-1) T: ambient temperature (K) fom:weight fraction of the total suspended particulate matter that is absorbing om phase (includes inorganic species and water that may be present) MWom: mean molecular weight of the species constituting the liquid organic matter (om) phase (g mol-1)

Organic Vapors “seed” particles If the compound i attains its Csat,i

SecondarySpecies

In laboratory experiments initial monoterpene concentration is very high (up to 700 ppbv) and saturation concentrations are rapidly surpassed.

The absence of pre-existing aerosol causes that both organic content (fom) and activity coefficient (γi) values approach unity.

The presence of other biogenic semi-volatile organic compounds emitted as primary aerosol cannot be understood and evaluated under laboratory conditions.

pump

GFF

PUF

Oxidant Denuder system

aerosol

PUF = Cgas,i

GFF = Caer,i

Mean concentration (ng m-3) of secondary aerosol components in gas (Cgas,i) and the particulate (Caer,i) phase

Sampling Period   6 - 12 12 - 18 18 - 6

Mean Temp. (Range)

K 287.3 (277.5 – 295.7)

294.3 (290.3 – 295.5)

287.5 (281.0 – 296.7)

cis- and trans-Pinonic Acid

Cgas,i 8.52 3.91 1.53

Caer,i 9.68 1.16 3.99

cis- and trans-nor Pinonic Acid

Cgas,i 2.65 0.32 3.18

Caer,i 1.94 0.14 1.51

cis-Pinic AcidCgas,i 3.77 2.37 0.41

Caer,i 2.38 0.49 3.03

PinonaldehydeCgas,i 0.73 5.06 1.06

Caer,i 0.78 0.27 0.88

NopinoneCgas,i 0.56 1.04 0.38

Caer,i 0.17 0.02 0.24

Sampling Period 6 - 12 12 - 18 18 - 6

Mean Temp. (Range) K 287.3(277.5 – 295.7)

294.3(290.3 – 295.5)

287.5(281.0 – 296.7)

n-Alkanols (C20 and C22)

Cgas,i 0.33 1.04 0.50

Caer,i 1.08 0.90 0.25

n-Alkanoic Acids (C12-C30)

Cgas,i 324. 08 85.44 57.56

Caer,i 84.95 27.38 31.44

n-Alkenoic Acids (C15:1-C18:1)

Cgas,i 47.52 11.54 11.63

Caer,i 32.30 10.10 16.68

α,ω-Dicarboxylic Acids (α,ω-C9)

Cgas,i 2.59 0.69 0.22

Caer,i 0.47 0.16 0.31

Mean concentration (ng m-3) of primary aerosol components in gas (Cgas,i) and the particulate (Caer,i) phase

Compound Stoichiometric Factor

i (dimensionless)

Partitioning Coefficient

Kom (m3 μg-1)

cis- and trans-Pinonic Acid (C10) 0.078 0.170

cis- and trans- nor-Pinonic Acid (C9) 0.013 0.097

cis-Pinic Acid (C10) 0.073 0.253

Pinonaldehyde (C9) 0.014 0.042

Nopinone (C9) 0.007 0.029

0

20

40

60

80

100

120

0 6 12 18 0 6 12

O3

(ppb

v) /

OH

. 105

cm-3

0,0

0,5

1,0

1,5

2,0

Mon

oter

pene

s (p

pbv)

Oxidation Content OH radicalsMonoterpenes

280

285

290

295

300

0 6 12 18 0 6 12

Tem

pera

ture

(K

)

0

100

200

300

400

0 6 12 18 0 6 12

PS

Con

cent

ratio

n (n

g m-3

)

PS (PP)

PS (GP)

Aerosol Formation Mechanism[OH, O3, T : from Harrison et al. (2001), Greasy eta l. (2001), Carslaw et al. (2001)]

8129,333336766,15385

2486,66667

0

2000

4000

6000

8000

10000

0 6 12 18 0 6 12Time period

Par

ticl

e N

um

ber

(p

art/

cm3

)

Primary organic aerosol components represented an important fraction of the atmospheric gas phase organic content.

The gas and particle atmospheric concentration of organic compounds directly-emitted from conifer leaf epicuticular wax and of those formed through the photo-oxidation of α- and β-pinene were simultaneously collected and measured in a conifer forest.

The saturation concentrations (Csat) of photo-oxidation products were estimated, by taking into consideration primary gas- and particle-phase organic species.

…

Summary

The results of this study indicated that primarily emitted organic species and ambient temperature

play a crucial role in secondary organic aerosol formation.

Csat of photo-oxidation products have been lowered facilitating new particle formation between molecules of photo-oxidation products and semi-volatile organic compounds.

From the measured concentrations of the above-mentioned compounds, (Csat) of α- and β-pinene photo-oxidation products were calculated for non-ideal conditions using a previously developed absorptive model.

Acknowledgements

• Dr. M. Mandalakis (University of Crete) for sampling • The OSOA group

• The European Commission (Environment and Climate Programme) project Origin and Formation of Secondary Organic Aerosol (OSOA)

• Research Committee of the University of Crete