and Earth System Sciences
Open Access
Atmospheric Chemistry and Physics
en Access
pen Access
Natural Hazards and Earth System Sciences
Discussions
Discussions
This discussion paper is/hasMeasurement been under review for the journal Atmospheric Chemistry Measurement and Physics (ACP). Please refer to the corresponding final paper in ACP if available. Techniques Techniques
Open Access
Atmospheric
Open Access
Atmospheric
Open Access
Atmos. Chem. Phys. Discuss., 13, 16925–16960, 2013 Atmospheric www.atmos-chem-phys-discuss.net/13/16925/2013/ Chemistry doi:10.5194/acpd-13-16925-2013 and Physics © Author(s) 2013. CC Attribution 3.0 License.
Discussions
Discussions
Open Access
Open Access
Discussions
Open Access
Open Access
Biogeosciences Reactivity ofBiogeosciences chlorine radical with submicron palmitic acid particles: Climate Climate kinetic measurements and products of the Past of the Past identification 1,*
1
1
Open Access
1
Open Access
, S. Gosselin , and System D. Petitprez M. Mendez , R. Ciuraru Earth System , S. Batut , N. Visez Earth Dynamics Dynamics 1 1
1
Open Access
Open Access
Discussions Laboratoire Physicochimie des Processus de Combustion et de l’Atmosphère (PC2A) UMR 8522 CNRS-Université Lille 1, 59655, Villeneuve d’Ascq, France * now at: IRCELYON, Institut deGeoscientific Recherches sur la Catalyse et l’Environnement de Lyon, Geoscientific UMR 5256 CNRS-UniversitéInstrumentation Lyon, Université Lyon 1, 69926 Villeurbanne Cedex, France Instrumentation Methods and Methods and Received: 24 April 2013 – Accepted: 9 May 2013 – Published: 25 June 2013 Data Systems Data Systems Discussions Correspondence to: D. Petitprez (
[email protected])
Hydrology and Earth System Sciences
Open Access
Open Access
Hydrology and Earth System 16925 Sciences
Discussions
Open Access
Model Development
Open Access
Geoscientific Published by Copernicus Publications on behalf of the European Geosciences Union. Geoscientific Model Development
Discussions
Ocean Science Discussions
Open Access
Open Access
Ocean Science Abstract
1
25
Open Access
20
Open Access
15
Open Access
10
Open Access
5
· Solid The heterogeneous reaction Solid of Cl Earth radicals with sub-micron palmitic acidEarth (PA) particles Discussions was studied in an aerosol flow tube in the presence or in the absence of O2 . Fine particles were generated by homogeneous condensation of PA vapors and introduced in the reactor where chlorine atoms are produced by photolysis of Cl2 using UV lamps surrounding the reactor. The effective reactive uptake coefficientThe (γ) Cryosphere has been determined The Cryosphere Discussions from the rate loss of PA measured by GC/MS analysis of reacted particles as a function of the chlorine exposure. In the absence of O2 , γ = 14 ± 5 indicates efficient secondary chemistry involving Cl2 . GC/MS analyses have shown the formation of monochlorinated and polychlorinated compounds in the oxidized particles. Although, the PA particles are solid, the complete mass can be consumed. In the presence of oxygen, the reaction is still dominated by secondary chemistry but the propagation chain length is smaller than in the absence of O2 which leads to an uptake coefficient γ = 3 ± 1. In the particulate phase, oxocarboxylic acids and dicarboxylic acids are identified by GC/MS. Formation of alcohols and monocarboxylic acids are also suspected. All these results show that solid organic particles could be efficiently oxidized by gas-phase radicals not only on their surface, but also in bulk by mechanisms which are still unclear. Furthermore the identified reaction products are explained by a chemical mechanism showing the pathway of the formation of more functionalized products. They help to understand the aging of primary tropospheric aerosol containing fatty acids.
Introduction
The concentration of organic matter in marine environments exhibits a seasonal behaviour, which dominates the chemical composition of fine particulate matter during periods of high biological activity (Yoon et al., 2007; O’Dowd et al., 2004; Cavalli et al., 2004; Sciare et al., 2008). Cells of living organisms in the oceans decompose after their death and the hydrophobic cellular constituents accumulate on the water surface 16926
5
10
15
20
25
forming a sea-surface micro-layer of 1 to 1000 µm thickness (Hardy, 1982). When seasalt aerosols (SSA) are generated by the mechanical ejection of droplets from waves and winds, these organic compounds are also ejected, thus becoming a component of the newly formed particles (Barger and Garrett, 1976; Gogou et al., 1998; Marty et al., 1979). Recent laboratory and field measurements have shown that the ratio of the organic mass fraction of SSA increases from 0.1 to near 1 when the ambient aerosol aerodynamic diameter decreases from 1 to 0.1 µm (Keene et al., 2007; Facchini et al., 2008). The exact mechanism for such large organic mass fraction of submicron SSA is not well understood. Chemical analyses of organic compounds sampled in SSA allowed to identify fatty acid (C12–C18) compounds (Marty et al., 1979), representing up to 10 % in mass of the total organic content of the particles (Mochida et al., 2002). Molecular characterization of sea-salt aerosol collected in marine air masses shows that fatty acids (FA) consist of relatively short carbon chains (Tervahattu et al., 2002b; Tervahattu et al., 2002a; Mochida et al., 2002; Oros and Simoneit, 2001). Due to the hydrophobic properties of surfactants, the fatty acids are thought to form an organic coating around the inorganic core of the particles (Ellison et al., 1999; Rudich, 2003). When considering a monolayer coating, the surface coverage by FA is estimated to be on the order of 0.3 to 14 % (Tervahattu et al., 2005; Mochida et al., 2002). Fatty acids are also ubiquitous in airborne particles sampled in urban atmospheres (Oliveira et al., 2007). They are found to contribute to up to 50 % of identified organic compounds from emission sources such as biomass burning (Nolte et al., 2001; Schauer et al., 2001; Fine et al., 2001), cooking (Schauer et al., 2002; He et al., 2004), and automobiles (He et al., 2006). Among the fatty acids, palmitic acid (C16 H32 O2 ) is the most abundant one (Mochida et al., 2002). Recent literature reviews present the physical and chemical processes which occur at the interface of airborne organic particles (Donaldson and Vaida, 2006; Rudich, 2003; George and Abbatt, 2010). Many heterogeneous reactions of atmospheric particles involve the main oxidant of the atmosphere (i.e. the hydroxyl radical OH· ) which 16927
5
10
15
20
25
chemically alters their surfaces thus aging them. The intensity of this aging depends on various parameters such as meteorological conditions, size of the particle, and the chemical composition of the particle surface and bulk. Consequently, the variability of these parameters leads to the observed spatial and temporal variability of the physical and chemical properties of atmospheric aerosols. These heterogeneous processes affect the optical, hygroscopic and reactive properties of airborne particles thereby making uncertain the prediction of their global and regional atmospheric impact. Although the OH· radical is the primary daytime oxidant, halogen atoms (Cl, Br and I) may also significantly participate in oxidation processes, especially in the marine boundary layer (MBL). Halogen species are emitted from anthropogenic sources, but important sources are also represented by the halogen-release from sea-salt aerosols and asso· ciated heterogeneous reactions. Cl atoms are mainly generated from the photolysis of active chlorine species and their concentrations can be up to 106 atom cm−3 (Spicer et al., 1998; Pechtl and von Glasow, 2007). Recent atmospheric measurements (Osthoff et al., 2008) have shown that nitryl chloride (ClNO2 ) is produced by heterogeneous reactions on sea-salt particles and accumulates during the night. At dawn, the photolysis of nitryl chloride produces a peak of Cl· with an estimated rate of formation of 1 × 106 atom cm−3 s−1 . This Cl· atom source seems modest relative to other oxidants. However, it has been · · reported that Cl reacts faster than OH radicals with hydrocarbon compounds (Spicer et al., 1998) and may represent the major oxidant of the troposphere in coastal and · industrialized areas, especially at dawn, when concentrations of OH radicals are low. While sources of reactive halogen species and halogen chemistry in the troposphere are relatively well studied, detailed chemical processes are still unknown (George and Abbatt, 2010). · Given the high reactivity of Cl atoms with organic compounds and the ubiquity of · Cl and fatty acids in the troposphere, especially in the MBL, it is obvious that this heterogeneous reactivity must be considered. However, only a few experimental studies 16928
·
5
10
15
20
25
·
between gas-phase radicals (Cl or OH ) with condensed-phase organic compounds, including model organic surfaces, are reported. Uptake coefficients of OH· on pure palmitic acid (PA) particles between 0.8 and 1 have been reported by McNeill et al. (2008). The authors also measured uptake coefficients for thin PA film coatings on solid and liquid NaCl particles, obtaining lower values than for pure PA experiments (solid, γOH ≈ 0.3 and liquid, γOH ≈ 0.05). Experiments with chlorine atoms, generated from Cl2 photolysis, have also been considered as a model for radical-initiated oxidation chemistry which avoids the presence of reactive precursors or side-products during generation of OH· . The reactive uptake of Cl· atoms on self-assembled organic monolayers was studied by Moise and Rudich (Moise and Rudich, 2001) using a flow reactor coupled to a chemical ionization mass spec· trometer. The uptake coefficient, measured by recording the rate of loss of Cl radicals, was estimated to be in the range (0.1
