A volatility tandem differential mobility analyzer (VTDMA) was developed to allow fast field measurement of the volatile fraction of atmospheric aerosol particles in the particle size range 20-500 nm. In this VTDMA the volatile compounds are evaporated by heating the aerosol to a temperature between 25• C and 300• C. The heating unit is equipped with six symmetric columns kept at different temperatures that allow the heating temperature to be rapidly changed so that a higher temporal resolution can be achieved compared to a regular VTDMA. This work first focuses on the design and calibration of the heating units for the conditioning of a selected aerosol sample while minimizing sample losses due to thermophoresis and diffusion. The design was based on the modeling of the profiles of temperature and velocity and the behavior of a monodisperse aerosol in the heating units, using Computational Fluid Dynamics (CFD) Flow Modeling Software. This allowed for initial estimations of the heater dimensions and also calculation of the minimum length of heating tube needed to completely evaporate the aerosol particles at high temperature with sufficient residence time, as well as to cool the aerosol sample down to ambient temperature. Next, the aerosol heating rate and aerosol deposition losses within the flow tube were estimated, and re-condensation of volatilized compounds evaluated. Then the VTDMA was calibrated and tested in the laboratory to determine the transfer efficiency, and finally, atmospheric aerosols were analyzed, with the first results presented here. This work emphasizes the need for better standardization of thermo-desorbing units for atmospheric aerosol studies.

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The nature of atmospheric aerosols is extremely complex and often requires advanced analytical tools for the determination of its physical and chemical properties. In particular, the interaction of particles with atmospheric water is a complex function of both particle size and composition. The ability of a particle to grow in a humid environment can be measured by humidity tandem differential mobility analyzing techniques (H-TDMA). In this article, we present a new development combining thermo-desorption and humidification aerosol conditioning in series that allows to measure changes in the hygroscopic behavior of aerosol at 90% relative humidity (RH) after conditioning of the particle by thermo-desorption to a temperature between 25• C and 300• C. The main feature of this system, named Volatility Hygroscopic-Tandem Differential Mobility Analyzer (VH-TDMA), is to allow for rapid (10 minutes) series of scans to control particle response to 1-thermal conditioning, 2-RH increase to 90% and 3-a combination of both thermal and RH conditioning. The VH-TDMA is, therefore, suited to investigate particle ageing through a simple coupling of H-TDMA and V-TDMA performances.The aim of the present article is to describe the instrument design and to validate its performances by focusing on the measurement of hygroscopic behavior of pure inorganic particles such as sodium chloride or ammonium sulfate, as well as internally mixed organic-inorganic particles. Based on laboratory experiments and This is a contribution from the EUSAAR FP6 Integrated Infrastructure Initiative.Address correspondence to Paulo Villani, Université Blaise Pascal-OPGC-CNRS, Laboratoire de Meteorologie Physique, Aubiere, France. E-mail: p.villani@opgc.univ-bpclermont.fr applications to natural aerosols, we show that the VH-TDMA system can be used to investigate the hygroscopic properties of the non-volatile fraction of ambient sub-micrometer aerosols in the range of 20 to 150 nm and the influence of the more volatile fraction of the particle on hygroscopic growth.

Abstract. While primary marine aerosol (PMA) is an important part of global aerosol total emissions, its chemical composition and physical flux as a function of the biogeochemical properties of the seawater still remain highly uncharacterized due to the multiplicity of physical, chemical and biological parameters that are involved in the emission process. Here, two nutrient-enriched mesocosms and one control mesocosm, both filled with Mediterranean seawater, were studied over a 3-week period. PMA generated from the mesocosm waters were characterized in term of chemical composition, size distribution and size-segregated cloud condensation nuclei (CCN), as a function of the seawater chlorophyll a (Chl a) concentration, pigment composition, virus and bacteria abundances. The aerosol number size distribution flux was primarily affected by the seawater temperature and did not vary significantly from one mesocosm to the other. The aerosol number size distribution flux was primarily affected by the seawater temperature and did not vary significantly from one mesocosm to the other. Particle number and CCN aerosol fluxes increase by a factor of 2 when the temperature increases from 22 to 32 • C, for all particle submicron sizes. This effect, rarely observed in previous studies, could be specific to oligotrophic waters and/or to this temperature range. In all mesocosms (enriched and control mesocosms), we detected an enrichment of calcium (+500 %) and a deficit in chloride (−36 %) in the submicron PMA mass compared to the literature inorganic composition of the seawater. There are indications that the chloride deficit and calcium enrichment are linked to biological processes, as they are found to be stronger in the enriched mesocosms. This implies a non-linear transfer function between the seawater composition and PMA composition, with comPublished by Copernicus Publications on behalf of the European Geosciences Union. plex processes taking place at the interface during the bubble bursting. We found that the artificial phytoplankton bloom did not affect the CCN activation diameter (D p,50,average = 59.85 ± 3.52 nm and D p,50,average = 93.42 ± 5.14 nm for supersaturations of 0.30 and 0.15 % respectively) or the organic fraction of the submicron PMA (average organic to total mass = 0.31 ± 0.07) compared to the control mesocosm. Contrary to previous observations in natural bloom mesocosm experiments, the correlation between the particle organic fraction and the seawater Chl a was poor, indicating that Chl a is likely not a straightforward proxy for predicting, on a daily scale, PMA organic fraction in models for all types of sea and ocean waters. Instead, the organic fraction of the Aitken mode particles were more significantly linked to heterotrophic flagellates, viruses and dissolved organic carbon (DOC). We stress that different conclusions may be obtained in natural (non-enriched) or non-oligotrophic systems.