Gas/particle partitioning of primary and secondary organic aerosol products in a boreal forest

1. Gas/particle partitioning of primary and secondary organic aerosol products 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

2. Biogenic Organic Aerosol Temp. Wind Epicuticular waxes Monoterpenes OH O3 NO3  ??? Low-vapor pressure multi-functional compounds 0.001 0.01 0.1 1 10 Diameter (μm)

3. Secondary Species Gas phase Particle phase Organic Vapors “seed” particles If the compound i attains its Csat,i Pankow’s (1994) model of gas/particle partitioning of semi-volatile organic compounds in an amorphous organic particle: Kp,i:partitioning coefficient of the i-compound (in m3μg-1) between the two phases PoL: 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)

4. 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.

5. GFF = Caer,i PUF = Cgas,i

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

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

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

11. Summary 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. Primary organic aerosol components represented an important fraction of the atmospheric gas phase organic content. The saturation concentrations (Csat) of photo-oxidation products were estimated, by taking into consideration primary gas- and particle-phase organic species. …

12. 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. Csat of photo-oxidation products have been lowered facilitating new particle formation between molecules of photo-oxidation products and semi-volatile organic compounds. The results of this study indicated that primarilyemitted organic species and ambient temperature play a crucial role in secondary organic aerosol formation.

13. 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