The surface properties of SOA generated from limonene and toluene using specific molecular probes: exploration of a new experimental technique

International audienceA new experimental technique of characterizing the aerosol-atmosphere surface has been explored using three examples: the secondary organic aerosols (SOA) resulting from the reaction of limonene with O3 and from the photooxidation of toluene in comparison with the combustion aerosol (soot) from a toluene diffusion flame. Rather than investigating the bulk composition of the aerosol by complete chemical analysis and identification of the many dozens if not more of constituent compounds we have interrogated the type and number of functional groups located at the aerosol surface by interacting them with specific molecular probes such as O3, NO2, N(CH3)3, and NH2OH to probe for the presence of oxidizable sites, acidic sites and carbonyl functionalities, respectively, that are present on the surface of the aerosol particle. In practice, typical amounts of one to a few mg of laboratory-generated SOA of limonene, toluene and soot have been deposited on a PTFE membrane filter that subsequently has been transferred to a molecular flow reactor used for the titration reaction of the surface functional groups by the molecular probes. Absolute amounts Ni with i=O3, NO2, N(CH3)3, NH2OH of probe molecules taken up by the filter sample measured using molecular beam sampling mass spectrometry have been converted into the number of surface group functionalities per unit surface area S using the aerosol particle distribution function (PDF) of limonene and toluene SOA and the BET total surface area of toluene flame soot to result in Ni/S. Arguments are presented that support the transfer of the PDF of the suspended to the aerosol collected on the Teflon filter

Neutrons for probing the ice nucleation on atmospheric soot particles

Soot resulting from combustion of kerosene in aircraft engines can act as condensation nuclei for water/ice in the atmosphere and promote the formation of contrails that turn into artificial cirrus clouds and affect the climate. The mechanisms of nucleation of water/ice particles are not well identified. Studies “in situ” are difficult to realize, so we try to determine by neutron diffraction the nucleation of water/ice adsorbed on soot collected at the outlet of an aircraft engine combustor within the conditions of the upper troposphere. The results are compared with those obtained on model laboratory soot. The comparison highlights the role of chemical impurities and structural defects of original aircraft engine soot on the nucleation of water/ice in atmospheric conditions

Indirect nanoplasmonic sensing

International audienceIndirect nanoplasmonic sensing (INPS) lets us to follow the adsorption of gases by a sensor composed of chemically active nanoparticles deposited onto a regular array of gold nanodisks fabricated using electron-beam lithography. We measured visible and infrared optical absorption spectra corresponding to localized surface plasmon resonance (LSPR) signals of the gold disks. While the gas molecules are adsorbed onto nanoparticles, the changes in the refractive index and other properties of the nanoparticle surfaces result in a spectral shift of the signal absorption maxima of LSPR corresponding to the underlying gold disk sensor [1]. We illustrate this work by adsorption of water vapor molecules on both hydrophilic and hydrophobic soot nanoparticles quantitatively followed by a calibrated INPS sensor [2] and we will give some perspectives concerning catalytic heterogeneous reactions. Indeed INPS coupled to mass spectrometry is a method of choice to characterize quantitatively and with a high sensitivity the reactivity of gases (CO, NOx, …) with metallic nanoparticles (Pt, Pd, …) involved in catalysis.References[1] E. M. Larsson, C. Langhammer, I. Zoric, B. Kasemo, Science 326, 1091-1094 (2009).[2] B. Demirdjian, F. Bedu, A. Ranguis, I. Ozerov, A. Karapetyan and C. R. Henry, The Journal of Physical Chemistry Letters 6, 4148-4152 (2015)

Impact of the 0.1% fuel sulfur content limit in SECA on particle and gaseous emissions from marine vessels

Emissions were measured on-board a ship in the Baltic Sea, which is a sulfur emission control area (SECA), before and after the implementation of the strict fuel sulfur content (FSC) limit of 0.1 m/m% S on the 1st of January 2015. Prior to January 2015, the ship used a heavy fuel oil (HFO) but switched to a low-sulfur residual marine fuel oil (RMB30) after the implementation of the new FSC limit. The emitted particulate matter (PM) was measured in terms of mass, number, size distribution, volatility, elemental composition, content of organics, black and elemental carbon, polycyclic aromatic hydrocarbons (PAHs), microstructure and micro-composition, along with the gaseous emissions at different operating conditions. The fuel change reduced emissions of PM mass up to 67%. The number of particles emitted remained unchanged and were dominated by nanoparticles. Furthermore, the fuel change resulted in an 80% reduction of SO2 emissions and decreased emissions of total volatile organic compounds (VOCs). The emissions of both monoaromatic and lighter polyaromatic hydrocarbon compounds increased with RMB30, while the heavy, PM-bound PAH species that belong to the carcinogenic PAH family were reduced. Emissions of BC remained similar between the two fuels. This study indicates that the use of low-sulfur residual marine fuel oil is a way to comply with the new FSC regulation and will reduce the anthropogenic load of SO2 emissions and secondary PM formed from SO2. Emissions of primary particles, however, remain unchanged and do not decrease as much as would be expected if distilled fuel was used. This applies both to the number of particles emitted and some toxic components, such as heavy metals, PAHs or elemental carbon (EC). The micro-composition analyses showed that the soot particles emitted from RMB30 combustion often do not have any trace of sulfur compared with particles from HFO combustion, which always have a sulfur content over 1%m/m. The soot sulfur content can impact aging and cloud condensation properties. This study is an in-depth comparison of the impact of these two fuels on the emissions of particles as well as their composition and microstructure. To evaluate the impact of the use of low-sulfur residual marine fuel oils on emissions from ships, additional research is needed to investigate the varied fuel types and compositions as well as the wide range of engine conditions and properties

Characterization of aircraft engine soot: unique properties and cloud impact

International audienceAircraft engine soot collected at the outlet of a D30KU combustor is comprehensively characterized by numerical experimental techniques: TEM, EDS, AFM, FTIR, GC-MS, ion and liquid chromatography and gravimetry. Physical properties (morphology, microstructure, particle size, surface area, porosity) and chemical properties (elemental composition, water soluble/insoluble organic and inorganic fraction, surface functional groups, and volatility) are examined. The water uptake by engine soot is analyzed in a wide range of the relative humidity from 0.01 to 100% and temperatures from 233K to 295K. Engine soot exhibits unique features and especially a high hydrophilicity (20ML of adsorbed water at 240K) and an heterogeneity of its composition. Comparison with laboratory–made kerosene flame soot indicates that engine soot particles separates into two fractions: an hydrophobic main fraction which contains a reduced amount of sulfur and an hydrophilic fraction of impurities with large amounts of iron, oxygen, sulfur and potassium. These results allows us to estimate the environmental conditions able to develop aircraft engine soot indirect effects with respect to ice nucleation modes proposed for contrail and cirrus formation. Our finding of two fractions in engine soot leads us to suggest that the main fraction of aircraft – generated soot may initiate a sulfur-independent heterogeneous nucleation mode in the UT while the fraction of impurities is responsible for contrail formation