Article Monoterpenes (MT) and Sesquiterpenes
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Atmos. Chem. Phys., 17, 12509–12531, 2017 https://doi.org/10.5194/acp-17-12509-2017 © Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License. Modelling organic aerosol concentrations and properties during ChArMEx summer campaigns of 2012 and 2013 in the western Mediterranean region Mounir Chrit1, Karine Sartelet1, Jean Sciare2,7, Jorge Pey3,a, Nicolas Marchand3, Florian Couvidat4, Karine Sellegri5, and Matthias Beekmann6 1CEREA, Joint Laboratory École des Ponts ParisTech – EDF R&D, Université Paris-Est, 77455 Champs-sur-Marne, France 2LSCE, CNRS-CEA-UVSQ, IPSL, Université Paris-Saclay, Gif-sur-Yvette, France 3Aix-Marseille University, CNRS, LCE UMR 7376, Marseille, France 4INERIS, Verneuil-en-Halatte, France 5Laboratoire de Météorologie Physique (LaMP), UMR 6016 CNRS/UBP, of the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Aubière, France 6LISA, UMR CNRS 7583, IPSL, Université Paris-Est Créteil and Université Paris Diderot, France 7EEWRC, The Cyprus Institute, Nicosia, Cyprus anow at: The Geological Survey of Spain, IGME, 50006 Zaragoza, Spain Correspondence to: Mounir Chrit ([email protected]) Received: 4 April 2017 – Discussion started: 29 May 2017 Revised: 25 August 2017 – Accepted: 15 September 2017 – Published: 23 October 2017 Abstract. In the framework of the Chemistry-Aerosol simulated water-soluble organic carbon (WSOC) concentra- Mediterranean Experiment, a measurement site was set up tions show that even at a remote site next to the sea, about at a remote site (Ersa) on Corsica Island in the northwest- 64 % of the organic carbon is soluble. The concentrations of ern Mediterranean Sea. Measurement campaigns performed WSOC vary with the origins of the air masses and the com- during the summers of 2012 and 2013 showed high or- position of organic aerosols. The marine organic emissions ganic aerosol concentrations, mostly from biogenic origin. only contribute to a few percent of the organic mass in PM1, This work aims to represent the organic aerosol concentra- with maxima above the sea. tions and properties (oxidation state and hydrophilicity) us- ing the air-quality model Polyphemus with a surrogate ap- proach for secondary organic aerosol (SOA) formation. Bio- 1 Introduction genic precursors are isoprene, monoterpenes and sesquiter- penes. In this work, the following model oxidation products The Mediterranean region is considered as one of the most of monoterpenes are added: (i) a carboxylic acid (MBTCA) prominent regions to be detrimentally impacted by climate to represent multi-generation oxidation products in the low- and air composition changes over both southern Europe and NOx regime, (ii) organic nitrate chemistry and (iii) ex- northern Africa. Organic aerosols (OA) account for about tremely low-volatility organic compounds (ELVOCs) formed 20–50 % of the fine aerosol mass at continental mid-latitudes by ozonolysis. The model shows good agreement of mea- (Saxena and Hildemann, 1996) and as high as 90 % in tropi- surements of organic concentrations for both 2012 and 2013 cal forest areas (Kanakidou et al., 2005; Jimenez et al., 2009). summer campaigns. The modelled oxidation property and They contribute to more than 50 % of EU-regulated PM2:5 hydrophilic organic carbon properties of the organic aerosols concentrations in Europe (Putaud et al., 2004). OA affect also agree reasonably well with the measurements. The influ- both climate and human health. They influence the radiation ence of the different chemical processes added to the model budget by mostly scattering sunlight resulting in negative di- on the oxidation level of organics is studied. Measured and rect radiative forcing (Fuzzi et al., 2006; Lin et al., 2014). Published by Copernicus Publications on behalf of the European Geosciences Union. 12510 M. Chrit et al.: Organic aerosol concentrations and properties during ChArMEx Moreover, hydrophilic OA can act as a cloud condensation Freney et al., 2017). In agreement with the observations of nuclei and hence modify cloud microphysical properties and El Haddad et al.(2013) in Marseille on the French Mediter- lifetime. In terms of health effects, OA toxicity is linked to ranean coast, the ground-based in situ measurements per- the oxidative stress which is induced by the reactive oxygen formed at the remote site of Ersa on Cape Corsica, the north- species. The oxidative potential may differ for the different ern tip of Corsica Island (southeast of continental France) organic precursors (Rattanavaraha et al., 2011; Jiang et al., showed that OA are mostly from biogenic origin. However, 2016; Tuet et al., 2017). as over urban areas, anthropogenic emissions from shipping OA are usually classified either as primary (POA) or sec- or pollution plumes from European big cities may influence ondary (SOA). POA are directly emitted in the atmosphere, biogenic SOA formation (Sartelet et al., 2012). often as intermediate/semivolatile organic compounds (I/S- The VOC biogenic precursors of SOA are isoprene, VOCs), which partition between the gas and the particle monoterpenes (MT) and sesquiterpenes. Although sesquiter- phases (Robinson et al., 2007). The gas phase of I/S-VOC penes emission factors are lower than those of isoprene and is missing from emission inventories (Couvidat et al., 2012; MT over Europe, their SOA yields are high because of their Kim et al., 2016). SOA are produced through chemical oxi- low saturation vapour pressures (Jaoui et al., 2013). For dation of volatile organic compounds (VOCs) and I/S-VOCs MT, first-generation oxidation products, such as pinonalde- and through condensation of I/S-VOCs. hyde, pinic and pinonic acids contribute to the formation of A large fraction of emitted VOCs is biogenic, especially in SOA, although their contributions may be low (Praplan et al., the western Mediterranean in summer, when solar radiation 2015). For α-pinene, further-generation oxidation steps may is high. Biogenic emissions may age and form SOA as they lead to the formation of very low-volatility products, such are transported through different environments (Hayes et al., as the tricarboxylic acid 3-methyl-1,2,3-butanetricarboxylic 2015). Using aerosol mass spectrometer (AMS) measure- acid (MBTCA; Müller et al., 2012; Kristensen et al., 2014) ments performed in an urban area in southern France (Mar- and oligomeric compounds. Ehn et al.(2014) and Kris- seille) and positive matrix factorisation techniques, El Had- tensen et al.(2014) showed that highly oxidised organic com- dad et al.(2011, 2013) attributed 80 % of the organic aerosol pounds are formed in the early stages of the oxidation of mass to biogenic secondary organic aerosols (BSOA) and MT. Rissanen et al.(2015) proposed a mechanistic descrip- near 40 % of the BSOA to monoterpene oxidation products. tion of these extremely low-volatility organic compounds These high biogenic concentrations in an urban area may (ELVOCs) formation from the most atmospherically abun- be partly explained by the influence of anthropogenic emis- dant biogenic monoterpenes, such as α-pinene and limonene. sions on biogenic SOA formation (Carlton et al., 2010; Hoyle These ELVOCs have been observed during both chamber and et al., 2011; Sartelet et al., 2012). in situ measurements in Germany (Mutzel et al., 2015). Sev- Similar results were obtained through measurement cam- eral studies showed the importance of nighttime SOA for- paigns in the Barcelona region (Spain), where Minguillón mation from MT via nitrate radical oxidation, resulting in et al.(2011, 2016) have found a prevalence of non-fossil or- the formation of organic nitrates (Pye et al., 2015; Bean ganic aerosol sources in remote and urban environments and and Ruiz, 2016; Xu et al., 2015; Nah et al., 2016). Pye clear evidence of biogenic VOC oxidation products and bio- et al.(2010) showed the importance of reactive nitrogen and genic SOA formation under anthropogenic stressors. pointed out the fact that organic nitrate accounts for more The ChArMEx (Chemistry and Aerosol Mediterranean than a half of the monoterpene oxidation products in the par- Experiment: http://charmex.lsce.ipsl.fr) project has organ- ticle phase over the US. ised several summer campaigns to study atmospheric chem- For isoprene, in low-NOx environments, recent stud- istry and its impacts in the western Mediterranean region. ies have focused on the formation of isoprene epoxydiols The TRAQA (Transport et Qualité de l’Air) campaign was (IEPOX) in acidic aerosols (Surratt et al., 2010; Couvidat set up in summer 2012 to study the transport and impact of et al., 2013b). However, using AMS measurements, particle- continental air on atmospheric pollution over the basin (Sicˇ phase IEPOX was not observed during the ChArMEx cam- et al., 2016). The ADRIMED (Aerosol Direct Radiative Im- paign over an isoprene-emitting forest in the south of France, pact in the Mediterranean; Mallet et al.(2016)) campaign suggesting it might have formed organosulfates (Freney was set up in June–July 2013 to assess the radiative impact et al., 2017). Several studies also showed the importance of of aerosols, while the SAF-MED (Secondary Aerosol For- non-IEPOX pathway for isoprene oxidation in low-NOx en- mation in the MEDiterranean) campaign was set up in July– vironment (Krechmer et al., 2015; Liu et al., 2016). Although early August 2013 to understand and characterise the con- ELVOCs may also form from isoprene oxidation, the yields centrations and properties of organic aerosols in the western may be low (Jokinen et al., 2015). Mediterranean and to figure out the origins of the high con- OA can also be emitted from the sea because of phyto- centrations observed outside urban areas. Intensive ground- plankton activity; according to O’Dowd et al.(2004), OA based in situ measurements were performed during the sum- from marine origin can contribute considerably to OA con- mer of 2013, while airborne measurements were performed centrations, especially near the biologically productive wa- during the summers 2013 and 2014 (Di Biagio et al., 2015; ters. Recently derived parameterisations (Gantt et al., 2012; Atmos.