Insights into the secondary fraction of the organic aerosol in a Mediterranean urban area: Marseille 1Universités d'Aix-Marseille-CNRS, UMR 6264: Laboratoire Chimie Provence, Equipe Instrumentation et Réactivité Atmosphérique, 13331 Marseille, France
07 Mar 2011
2Laboratoire de Chimie Moléculaire et Environnement, Université Savoie-Polytech'Savoie, Chambéry, France
3Université Joseph Fourier-Grenoble 1-CNRS, UMR 5183, Laboratoire de Glaciologie et Géophysique de l'Environnement, 38402 Saint Martin d'Hères, France
4Regional Network for Air Quality Monitoring (ATMO-PACA), 146 rue Paradis, 13006 Marseille, France
Received: 11 Jun 2010 – Published in Atmos. Chem. Phys. Discuss.: 01 Nov 2010 Abstract. A comprehensive aerosol characterization was conducted at Marseille during
summer, including organic (OC) and elemental carbon (EC), major ionic
species, radiocarbon (14C), water-soluble OC and HULIS (HUmic LIke
Substances), elemental composition and primary and secondary organic
markers. This paper is the second paper of a two-part series that uses this
dataset to investigate the sources of Organic Aerosol (OA). While the first
paper investigates the primary sources (El Haddad et al., 2010), this second
paper focuses on the secondary fraction of the organic aerosol.
Revised: 24 Feb 2011 – Accepted: 28 Feb 2011 – Published: 07 Mar 2011
In the context of overall OC mass balance, primary OC (POC) contributes on
average for only 22% and was dominated by vehicular emissions accounting
on average for 17% of OC. As a result, 78% of OC mass cannot be
attributed to the major primary sources and remains un-apportioned.
Radiocarbon measurements suggest that more than 70% of this fraction is
of non-fossil origin, assigned predominantly to biogenic secondary organic
carbon (BSOC). Therefore, contributions from three traditional BSOC
precursors, isoprene, $\alpha $-pinene and β-caryophyllene, were
considered. These were estimated using the ambient concentrations of
Secondary Organic Aerosol (SOA) markers from each precursor and
laboratory-derived marker mass fraction factors.
Secondary organic markers derived from isoprene photo-oxidation (ie:
2-methylglyceric acid and 2-methyltetrols) do not exhibit the same temporal
trends. This variability was assigned to the influence of NOx
concentration on their formation pathways and to their potential decay by
further processing in the atmosphere. The influence of changes in isoprene
chemistry on assessment of isoprene SOC contribution was evaluated
explicitly. The results suggest a 60-fold variation between the different
estimates computed using different isoprene SOC markers, implying that the
available profiles do not reflect the actual isoprene SOC composition
observed in Marseille.
Using the marker-based approach, the aggregate contribution from traditional
BSOC was estimated at only 4.2% of total OC and was dominated by α-pinene
SOC accounting on average for 3.4% of OC. As a result, these
estimates underpredict the inexplicably high loadings of OC. This
underestimation can be associated with (1) uncertainties underlying the
marker-based approach, (2) presence of other SOC precursors and (3) further
processing of fresh SOC, as indicated by organosulfates (RSO4H) and
HUmic LIke Substances (HULIS) measurements.
Citation: El Haddad, I., Marchand, N., Temime-Roussel, B., Wortham, H., Piot, C., Besombes, J.-L., Baduel, C., Voisin, D., Armengaud, A., and Jaffrezo, J.-L.: Insights into the secondary fraction of the organic aerosol in a Mediterranean urban area: Marseille, Atmos. Chem. Phys., 11, 2059-2079, doi:10.5194/acp-11-2059-2011, 2011.