Secondary Organic Aerosol - Formation Mechanisms and Source Contributions in Europe

Fine particulate matter (PM2.5) as an atmospheric pollutant is strongly related to increased mortality and morbidity. The empirically established link between aerosol concentration and human health compels increased efforts to reduce the atmospheric concentrations of fine particles. Organic material accounts for about 20-60% of the total PM2.5 and contains substances of known toxicity. It has been shown that in some areas secondary organic aerosol (SOA) accounts for 20% of the total organic aerosol throughout the year but can contribute up to 70% in smog episodes. The estimation of the sources and concentrations of organic aerosol is therefore crucial to the proper assessment of related health effects Part of this work attempts a critical review of the literature on SOA. The goal is to describe formation mechanisms, to identify likely precursor gases, and to estimate the SOA contribution to PM2.5. SOA forms by oxidation of volatile organic compounds (VOC). The aerosol yield varies significantly among different VOC species as well as source sectors and the contribution of SOA to the total particulate organic material is dependent on the time of the day and the season. The consequences of these findings for reduction strategies are discussed. The knowledge gained in the literature review is further used to exemplify a possible procedure to assess and compare the aerosol formation potential of some source sectors used in the RAINS model. It is found that traffic and solvent use in the printing industry and paint are important sectors for SOA production

Crossover from Single-Ion to Coherent Non-Fermi Liquid Behavior in Ce1−x_{1-x}Lax_xNi9_9Ge4_4

We report specific heat and magneto-resistance studies on the compound Ce${}_{1-x}$La${}_x$Ni${}_9$Ge${}_4$ for various concentrations over the entire stoichiometric range. Our data reveal single-ion scaling with Ce-concentration between $x = 0.1$ and 0.95. Furthermore, CeNi${}_9$Ge${}_4$ turns out to have the largest ever recorded value of the electronic specific heat $\Delta c/T \approx$ 5.5 J $\rm K^{-2}mol^{-1}$ at $T=0.08$ K which was found in Cerium f-electron lattice systems. In the doped samples $\Delta c/T$ increases logarithmically in the temperature range between 3 K and 50 mK typical for non-Fermi liquid (nFl) behavior, while $\rho$ exhibits a Kondo-like minimum around 30 K, followed by a single-ion local nFl behavior. In contrast to this, CeNi${}_9$Ge${}_4$ flattens out in $\Delta c/T$ below 300 mK and displays a pronounced maximum in the resistivity curve at 1.5 K indicating a coherent heavy fermion groundstate. These properties render the compound Ce${}_{1-x}$La${}_x$Ni${}_9$Ge${}_4$ a unique system on the borderline between Fermi liquid and nFl physics.Comment: 2 pages, 3 figures, SCES0

Technical Note: Characterization of a static thermal-gradient CCN counter

International audienceThe static (parallel-plate thermal-gradient) diffusion chamber (SDC) was one of the first instruments designed to measure cloud condensation nuclei (CCN) concentrations as a function of supersaturation. It has probably also been the most widely used type of CCN counter. This paper describes the detailed experimental characterization of a SDC CCN counter, including calibration with respect to supersaturation and particle number concentration. In addition, we investigated the proposed effect of lowered supersaturation because of water vapor depletion with increasing particle concentration. The results obtained give a better understanding why and in which way it is necessary to calibrate the SDC CCN counter. The calibration method is described in detail and can, in parts, be used for calibrations also for other types of CCN counters. We conclude the following: 1) it is important to experimentally calibrate SDC CCN counters with respect to supersaturation, and not only base the supersaturation on the theoretical description of the instrument; 2) the number concentration calibration needs to be performed as a function of supersaturation, also for SDC CCN counter using the photographic technique; and 3) we observed no evidence that water vapor depletion lowered the supersaturation

Technical note: A method for measuring size-resolved CCN in the atmosphere

International audienceWe present a method to investigate cloud condensation nuclei (CCN) concentrations and activation efficiencies as a function of two independent variables, aerosol particle size and water vapor supersaturation. To date, most ambient CCN measurements have been made as the integral (total) CCN concentration as a function of water vapor supersaturation only. However, since CCN properties of aerosol particles are strongly dependent on particle size, as well as on chemical composition, which commonly varies with particle size, more detailed measurements can provide additional important information about the CCN activation. With size-resolved measurements, the effect of particle size on CCN activity can be kept constant, which makes it possible to directly assess the influence of particle chemistry. The instrumental set-up consists of a differential mobility analyzer (DMA) to select particles of a known size, within a narrow size range. A condensation nuclei (CN) counter (condensation particle counter, CPC) is used to count the total number of particles in that size range, and a CCN counter is used to count the number of CCN as a function of supersaturation, in that same size range. The activation efficiency, expressed as CCN/CN ratios, can thus directly be calculated as a function of particle size and supersaturation. We present examples of the application of this technique, using salt and smoke aerosols produced in the laboratory as well as ambient aerosols

Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment

International audienceExperimental and theoretical uncertainties in the measurement of cloud condensation nuclei (CCN) with a continuous-flow thermal-gradient CCN counter from Droplet Measurement Technologies (DMT-CCNC) have been assessed by model calculations and calibration experiments with ammonium sulfate and sodium chloride aerosol particles in the diameter range of 20?220 nm. Experiments have been performed in the laboratory and during field measurement campaigns, extending over a period of more than one year and covering a wide range of operating conditions (650?1020 hPa ambient pressure, 0.5?1.0 L min?1 aerosol flow rate, 20?30°C inlet temperature, 4?34 K m?1 temperature gradient). For each set of conditions, the effective water vapor supersaturation (Seff) in the CCNC was determined from the measured CCN activation spectra and Köhler model calculations. High measurement precision was achieved under stable laboratory conditions, where relative variations of Seff in the CCNC were generally less than ±2%. During field measurements, however, the relative variability increased up to ±5?7%, which can be mostly attributed to variations of the CCNC column top temperature with ambient temperature. To assess the accuracy of the Köhler models used to calculate Seff, we have performed a comprehensive comparison and uncertainty analysis of the various Köhler models and thermodynamic parameterizations commonly used in CCN studies. For the relevant supersaturation range (0.05?2%), the relative deviations between different modeling approaches were as high as 25% for (NH4)2SO4 and 16% for NaCl. The deviations were mostly caused by the different parameterizations for the activity of water in aqueous solutions of (NH4)2SO4 and NaCl (activity parameterization, osmotic coefficient, and van't Hoff factor models). The uncertainties related to the model parameterizations of water activity clearly exceeded the CCNC measurement precision. Relative deviations caused by different ways of calculating or approximating solution density and surface tension did not exceed 3% for (NH4)2SO4 and 1.5% for NaCl. Nevertheless, they did exceed the CCNC measurement precision under well-defined operating conditions and should not be neglected in studies aimed at high accuracy. To ensure comparability of results, we suggest that CCN studies should always report exactly which Köhler model equations and parameterizations of solution properties were used. Substantial differences between the CCNC calibration results obtained with (NH4)2SO4 and NaCl aerosols under equal experimental conditions (relative deviations of Seff up to ~10%) indicate inconsistencies between widely used activity parameterizations derived from electrodynamic balance (EDB) single particle experiments (Tang and Munkelwitz, 1994; Tang, 1996) and hygroscopicity tandem differential mobility analyzer (HTDMA) aerosol experiments (Kreidenweis et al., 2005). Therefore, we see a need for further evaluation and experimental confirmation of preferred data sets and parameterizations for the activity of water in dilute aqueous (NH4)2SO4 and NaCl solutions. The experimental results were also used to test the CCNC flow model of Lance et al.~(2006), which describes the dependence of Seff on temperature, pressure, and flow rate in the CCN counter. This model could be applied after subtraction of a near-constant temperature offset and derivation of an instrument-specific thermal resistance parameter (RT?1.8 K W?1). At Seff>0.1% the relative deviations between the flow model and experimental results were mostly less than 5%, when the same Köhler model approach was used. At Seff?.1%, however, the deviations exceeded 20%, which can be attributed to non-idealities which also caused the near-constant temperature offset. Therefore, we suggest that the CCNC flow model can be used to extrapolate calibration results, but should generally be complemented by calibration experiments performed under the relevant operating conditions ? during field campaigns as well as in laboratory studies

Stable carbon and nitrogen isotope ratio in PM1 and size segregated aerosol particles over the Baltic Sea

We analysed delta C-13 of total carbon (TC) and PN of total nitrogen (TN) in submicron (PM1) and size segregated aerosol particles ( PM0.056-2.5) collected during a cruise in the Baltic Sea from 9 to 17 November 2012. PM1 were characterized by the highest delta C-13 (-26.4 parts per thousand) and lowest delta N-15 (-0.2 and 0.8 parts per thousand) values when air masses arrived from the southwest direction (Poland). The obtained delta C-13 values indicated that combined emissions of coal and diesel/gasoline combustion were the most likely sources of TC. The depleted delta N-15 values indicated that TN originated mainly from liquid fuel combustion (road traffic, shipping) during this period. The lowest PC and highest delta N-15 values were determined in PM1 samples during the western airflow when the air masses had no recent contact with land. The highest delta N-15 values were probably associated with chemical aging of nitrogenous species during long-range transport, the lowest delta C-13 values could be related to emissions from diesel/gasoline combustion, potentially from ship traffic. The delta C-13 analysis of size-segregated aerosol particles PM0.056-2.5 revealed that the lowest delta C-13 values were observed in the size range from 0.056 to 0.18 mu m and gradual C-13 enrichment occurred in the size range from 0.18 to 2.5 mu m due to different sources or formation mechanisms of the aerosols

Seasonal changes of sources and volatility of carbonaceous aerosol at urban, coastal and forest sites in Eastern Europe (Lithuania)

We measured stable carbon isotope ratios of total carbon (TC) and organic carbon (OC) in fine carbonaceous aerosol fraction sampled in August and September 2013 at urban, coastal and forest sites in Lithuania. δ13C values of TC for all three sites over the whole measurement period varied from −29.3 to −26.6‰, which is in the range of particles emitted by fossil fuel combustion in Eastern Europe. The isotopic composition at the forest and coastal site showed a similar variation during two contrasting pollution periods. δ13C values in the clean period were more variable, whereas the polluted period was characterized by a gradual enrichment in δ13C compared to the clean period. In the polluted period air masses originated from southern, southeastern or southwestern direction, indicating long-range transport of pollutants from Eastern Europe and Southern Europe to Lithuania. Oxidative processing during long-range transport or the different source signatures (e.g., enriched 13C signature of gasoline used in Western Europe vs. Eastern Europe) could cause the less negative δ13COC values during the polluted episode. δ13C for OC desorbed from the filter samples was separately measured during three different temperature steps (200 °C, 350 °C and 650 °C). OC desorbed at 200 °C had the most depleted 13C signature of around −29‰ at all three sites. A comparison with previously published data measured during the winter at the same sites showed that both TC and OC had less negative δ13C values in winter than in summer, which can be explained by the contribution of biomass/coal burning sources in winter. At the urban site δ13C of OC did not change much with increasing desorption temperature in winter, which is typical for primary sources, but in the summer δ13C of OC was depleted for lower desorption temperatures, possibly due to the influence of SOA formation. A higher fraction of more refractory OC in summer compared to winter-time suggests active photochemical processing of the primary organic aerosol as an important process at all three sites

Ceramic membranes for partial oxygenation of hydrocarbon fuels to high-value-added products

This report describes the design of a membrane reactor for converting methane into value added products. The design includes an outer tube of perovskite which contacts air, an inner tube of zirconium oxide which contacts methane, and a bonding layer of a mixture of zirconium oxide and perovskite

Isolated Non-Compaction of the Left Ventricle in a Patient with New-Onset Heart Failure: Morphologic and Functional Evaluation with Cardiac Multidetector Computed Tomography

We describe a case of new-onset heart failure in a patient in whom cardiac CT enabled the non-invasive diagnosis of isolated non-compaction and associated functional abnormalities of the left ventricle with the concomitant evaluation of coronary arteries. This case highlights the utility of cardiac CT for the morphological and functional evaluation of the heart as a single imaging modality

Water uptake by biomass burning aerosol at sub- and supersaturated conditions: closure studies and implications for the role of organics

We investigate the CCN activity of freshly emitted biomass burning particles and their hygroscopic growth at a relative humidity (RH) of 85%. The particles were produced in the Mainz combustion laboratory by controlled burning of various wood types. The water uptake at sub- and supersaturations is parameterized by the hygroscopicity parameter, κ (c.f. Petters and Kreidenweis, 2007). For the wood burns, κ is low, generally around 0.06. The main emphasis of this study is a comparison of κ derived from measurements at sub- and supersaturated conditions (κG and κCCN), in order to see whether the water uptake at 85% RH can predict the CCN properties of the biomass burning particles. Differences in κGand κCCN can arise through solution non-idealities, the presence of slightly soluble or surface active compounds, or non-spherical particle shape. We find that κG and κCCN agree within experimental uncertainties (of around 30%) for particle sizes of 100 and 150 nm; only for 50 nm particles is κCCN larger than κG by a factor of 2. The magnitude of this difference and its dependence on particle size is consistent with the presence of surface active organic compounds. These compounds mainly facilitate the CCN activation of small particles, which form the most concentrated solution droplets at the point of activation. The 50 nm particles, however, are only activated at supersaturations higher than 1% and are therefore of minor importance as CCN in ambient clouds. By comparison with the actual chemical composition of the biomass burning particles, we estimate that the hygroscopicity of the water-soluble organic carbon (WSOC) fraction can be represented by a κWSOC value of approximately 0.2. The effective hygroscopicity of a typical wood burning particle can therefore be represented by a linear mixture of an inorganic component with κ ≅ 0.6, a WSOC component with κ ≅ 0.2, and an insoluble component with κ = 0