Two different single particle mass spectrometers were operated in parallel at the Swiss High Alpine Research Station Jungfraujoch (JFJ, 3580 m a.s.l.) during the Cloud and Aerosol Characterization Experiment (CLACE 6) in February and March 2007. During mixed phase cloud events ice crystals from 5–20 μm were separated from larger ice aggregates, non-activated, interstitial aerosol particles and supercooled droplets using an Ice-Counterflow Virtual Impactor (Ice-CVI). During one cloud period supercooled droplets were additionally sampled and analyzed by changing the Ice-CVI setup. The small ice particles and droplets were evaporated by injection into dry air inside the Ice-CVI. The resulting ice and droplet residues (IR and DR) were analyzed for size and composition by the two single particle mass spectrometers: a custom-built Single Particle Laser-Ablation Time-of-Flight Mass Spectrometer (SPLAT) and a commercial Aerosol Time-of-Flight Mass Spectrometer (ATOFMS, TSI Model 3800). During CLACE 6 the SPLAT instrument characterized 355 individual IR that produced a mass spectrum for at least one polarity and the ATOFMS measured 152 IR. The mass spectra were binned in classes, based on the combination of dominating substances, such as mineral dust, sulfate, potassium and elemental carbon or organic material. The derived chemical information from the ice residues is compared to the JFJ ambient aerosol that was sampled while the measurement station was out of clouds (several thousand particles analyzed by SPLAT and ATOFMS) and to the composition of the residues of supercooled cloud droplets (SPLAT: 162 cloud droplet residues analyzed, ATOFMS: 1094). The measurements showed that mineral dust was strongly enhanced in the ice particle residues. Close to all of the SPLAT spectra from ice residues did contain signatures from mineral compounds, albeit connected with varying amounts of soluble compounds. Similarly, close to all of the ATOFMS IR spectra show a mineral or metallic component. Pure sulfate and nitrate containing particles were depleted in the ice residues. Sulfate and nitrate was found to dominate the droplet residues (~90% of the particles). The results from the two different single particle mass spectrometers were generally in agreement. Differences in the results originate from several causes, such as the different wavelength of the desorption and ionisation lasers and different size-dependent particle detection efficiencies.

We present here the development and first field deployment of a novel Aircraft-based Laser ABlation Aerosol MAss spectrometer (ALABAMA), which is capable of measuring the chemical composition and size of individual ambient aerosol particles in the size range between 150 and 900 nm. The instrument uses a continuous wave 532 nm laser to size and detect the particles, a pulsed 266 nm laser to ablate and ionize the particles, and a bipolar, Z-shaped time-of-flight mass spectrometer to detect positive and negative ions. The ALABAMA fits into a 19”-aircraft rack of 150 cm height and has a total weight of 140 kg, thus currently being one of the smallest and lightest-weight instruments of its type. We present a detailed characterization of ALABAMA with respect to particle beam width, detection and ablation efficiency, and example mass spectra of different particle types. The first aircraft-based field mission was performed within the MEGAPOLI summer campaign in July 2009 around Paris, France, onboard an ATR42 aircraft. During 11 research flights, corresponding to a total measuring time of approximately 44 hours, ALABAMA measured 6502 single particle mass spectra. The mass spectra were classified into eight particle classes using distinctive markers for each particle type. The most abundant particle types contained organic and secondary inorganic compounds. The results further show that differences in the abundance of observed particle types between different air masses are very pronounced when comparing air masses arriving from the greater Paris area with air masses arriving from other directions.

mospheric particles are thought to initiate the majority of terrestrial precipitation. Field-based measurements of ice-crystal residues, together with controlled environment experiments on artificial clouds, suggest that anthropogenic lead-containing particles are among the most efficient ice-forming substances in the atmosphere.

1 Leibniz-Institute for Tropospheric Research, Leipzig, Germany 2 Paul Scherrer Institute, Villigen, Switzerland 3 University of Mainz, Germany 4 Max Planck Institute Mainz, Germany 5 University of Darmstadt, Germany 6 University of Frankfurt, Germany 7 ETH Zürich, Switzerland 8 present affiliation: ECN Petten, The Netherlands 9 present affiliation: PNNL, Richland, USA 10 present affiliation: NOAA, Boulder, USA

By means of a newly designed portable aerosol mass spectrometer SPLAT (Single Particle Laser Ablation Time-of-flight mass spectrometer) for the analysis of single atmospheric aerosol particles we investigated the system performance in dependency on two different aerodynamic lenses (Liu and Schreiner type) capable of focusing particles with diameters ranging from 80 nm to 800 nm and 300 nm to 3000 nm, respectively. By using the pressure regulated Schreiner lens, the instrument is independent of variations in atmospheric pressure which would lead to changing dynamical properties of the aerosol particles. Active pressure control inside the inlet system facilitates airborne measurements without complicated corrections. With the Liu setup no pressure regulation was used. Here the overall efficiency of our instrument was 7% while with the Schreiner setup 2% was achieved. The Liu lens setup is optimal for measuring submicron particles at low particle concentrations. To detect supermicron particles the Schreiner lens setup is favored. Together with these experiments we present key details of the SPLAT setup and its characterization. Our instrument is able to measure simultaneously the size and the chemical composition of individual aerosol particles larger than 300 nm in diameter. It uses forward scattered light of single aerosol particles at two positions to determine their vacuum aerodynamic diameter from the flight time between the two lasers. Chemical analysis of the particles is done by laser ablation mass spectrometry utilizing a bipolar time-of-flight mass spectrometer.

Institute for Atmospheric Physics, Johannes Gutenberg-University, Mainz, D-55099, Germany Particle Chemistry Department, Max Planck Institute for Chemistry, Mainz, D-55020, Germany Institute for Atmospheric und Environmental Sciences, Johann Wolfgang Goethe-University, Frankfurt, D-60438, Germany Leibniz Institute for Tropospheric Research, Leipzig, D-04318, Germany Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, 5232, Switzerland

The oxidation of ethanol was studied in low-pressure, premixed flat flames using molecular beam mass spectrometry (MBMS) in combination with electron impact ionization (EI) and resonance-enhanced multiphoton ionization (REMPI). Flame temperature profiles were measured by laser-induced fluorescence (LIF) of seeded NO. Two ethanol/oxygen/argon flames with stoichiometries of ϕ=1.00 and ϕ=2.57 were investigated at 50 mbar by EI-MBMS. Profiles of a variety of stable and radical species were measured as a function of height above the burner. The benzene profile in the fuel-rich ethanol flame was obtained by REMPI-MBMS. The same technique was used to determine the dependence of the benzene concentration on the ethanol/propene ratio in low-pressure flames with blended fuels (propene/ethanol/oxygen/argon). The C/O ratio of all blends was kept constant at C/O=0.773 or C/O=0.600. Ethanol addition ranged from 0 to 15% for flames with C/O=0.773, and from 0 to 100% for flames with C/O=0.600. In both data sets, a decrease of the benzene concentration with increasing ethanol percentage was observed. Qualitative information on some other aromatic species with higher mass was also obtained.

The formation of small PAHs with up to three rings has been studied in fuel-rich, nonsooting premixed flames of propene–oxygen–argon and cyclopentene–oxygen–argon at C/O=0.77 and 50 mbar. Detailed species composition and temperature profiles for these flames had been studied before, using laser-induced fluorescence (LIF) and in situ molecular beam mass spectrometry (MBMS) with electron impact ionization (EI). These previous studies found a significant influence of the fuel structure upon the reaction pathways to benzene as the first aromatic ring. Here, the further molecular reaction sequence is studied with enhanced sensitivity, using MBMS coupled with resonance-enhanced multiphoton ionization (REMPI). Absolute concentrations of benzene were determined using both ionization strategies in order to establish a link to the previous investigations. The ratio of REMPI signals in the two flames for masses from m/z=78 (benzene) up to approximately m/z=200 is given and shows a predominant tendency of the cyclopentene flame to form aromatic species. The experimental results are complemented with simulations using two current chemical kinetic reaction models. The model predictions for important species in this mass range are discussed in the light of reaction flux and sensitivity analyses.

Soot is one of the most important pollutants originating from combustion. Despite recent advances in the measurement of size and composition of soot particles, their actual formation mechanism is still under debate. It depends on fuel, stoichiometry, temperature, flow conditions and the concentration of a large number of intermediate species. An adequate characterization of this complex reaction system generally requires the use of several complementary techniques.In this article, we present measurements aiming to study reactions in fuel-rich flames using several complementary techniques. Only with a combination of optical and mass-spectrometric measurements, important features of the early polyaromatic hydrocarbon (PAH) and soot formation chemistry are accessible in detail. Three different techniques are combined to investigate one-dimensional laboratory flames on the same low-pressure burner and their respective merits are discussed: (i) cavity ring-down spectroscopy (CRDS) for the detection of small radicals and measurement of the temperature, (ii) mass spectrometry with electron-impact (EI) ionization in order to measure species with molecular weights up to m/e = 90, and (iii) mass spectrometry with resonantly-enhanced multi-photon ionization (REMPI) to distinguish isomers with masses up to m/e = 178. Measurements of this type may prove a valuable input to improve kinetic and combustion models.

The cooling effect in molecular beam (MB) sampling from low-pressure flames and gas mixtures was investigated. Although the MB method is often used to study the flame structure of low-pressure flames, typically combined with mass spectrometric (MS) detection, it is poorly characterized. The temperature of the MB must be known, especially if species concentrations are to be measured with spectroscopic methods, like resonance-enhanced multiphoton ionization (REMPI) spectroscopy. In the present study, two independent MBMS instruments, which are very similar to those used previously by different groups, were investigated starting with pressures of 40 and 50 mbar in the burner chamber. The rotational temperatures of NO and benzene were determined using REMPI spectroscopy for different initial conditions; the ions were separated by time-of-flight mass spectrometers. Two REMPI excitation schemes were applied: for NO the first step was always the excitation of the A-X transition near 225 nm, while benzene was excited and ionized at wavelengths near 259 nor. Unexpectedly, molecular beams from cold-gas flows were cooled very slightly by 10%-25%. In the molecular beams derived from low-pressure flames, the cooling effect was stronger, with final rotational temperatures of 300-400 K, but the MB temperature was virtually independent of the initial temperature. A possible explanation of this finding would be that the cooling takes place to a large extent by wall collisions within the nozzle and to a lesser degree by intermolecular collisions.

Development and validation of detailed reaction mechanisms for fuel-rich combustion have a continuing need for quantitative experimental flame data. In this study, an overview is presented of recent experimental investigations of a series of fuel-rich premixed low-pressure flames burning acetylene, propene, linear and cyclic C5-alkenes and C5-alkanes with a combination of laser spectroscopy and molecular beam mass spectrometry (MBMS). Particular attention was devoted to the reaction pathways leading to the first aromatic ring. Fuel-specific aspects with respect to benzene formation are discussed. The potential of resonance-enhanced multi-photon ionisation (REMPI) MBMS as a quantitative technique for the measurement of stable species is examined for benzene as an example. Also, first results of the investigation of a fuel-rich ethanol flame under similar conditions are given. Advantages and potential drawbacks of the applied diagnostic methods are discussed in view of the importance of reliable, quantitative measurements for the understanding of fuel-rich chemistry preceding polycyclic aromatic hydrocarbon (PAH) and soot formation as well as for the related modelling of these chemical processes.

Soot formation is still one of the most pressing problems in combustion. Chemical mechanisms have been established which need to be examined in detail under laboratory conditions. Some of the main pathways concerning the formation of soot precursors are still under debate. While it seems commonly accepted that some of the dominant routes may be fuel-specific. experimental data and their comparison with kinetic models for fuels with more than 3 C atoms are scarce. This article will present an overview of the work pursued in Bielefeld on the characterisation of fuel-rich flames by a combination of laser spectroscopy and mass spectrometry. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.