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- ItemResults and recommendations from an intercomparison of six Hygroscopicity-TDMA systems(München : European Geopyhsical Union, 2011) Massling, A.; Niedermeier, N.; Hennig, T.; Fors, E.O.; Swietlicki, E.; Ehn, M.; Hämeri, K.; Villani, P.; Laj, P.; Good, N.; McFiggans, G.; Wiedensohler, A.The performance of six custom-built Hygrocopicity-Tandem Differential Mobility Analyser (H-TDMA) systems was investigated in the frame of an international calibration and intercomparison workshop held in Leipzig, February 2006. The goal of the workshop was to harmonise H-TDMA measurements and develop recommendations for atmospheric measurements and their data evaluation. The H-TDMA systems were compared in terms of the sizing of dry particles, relative humidity (RH) uncertainty, and consistency in determination of number fractions of different hygroscopic particle groups. The experiments were performed in an air-conditioned laboratory using ammonium sulphate particles or an external mixture of ammonium sulphate and soot particles. The sizing of dry particles of the six H-TDMA systems was within 0.2 to 4.2% of the selected particle diameter depending on investigated size and individual system. Measurements of ammonium sulphate aerosol found deviations equivalent to 4.5% RH from the set point of 90% RH compared to results from previous experiments in the literature. Evaluation of the number fraction of particles within the clearly separated growth factor modes of a laboratory generated externally mixed aerosol was done. The data from the H-TDMAs was analysed with a single fitting routine to investigate differences caused by the different data evaluation procedures used for each H-TDMA. The differences between the H-TDMAs were reduced from +12/−13% to +8/−6% when the same analysis routine was applied. We conclude that a common data evaluation procedure to determine number fractions of externally mixed aerosols will improve the comparability of H-TDMA measurements. It is recommended to ensure proper calibration of all flow, temperature and RH sensors in the systems. It is most important to thermally insulate the aerosol humidification unit and the second DMA and to monitor these temperatures to an accuracy of 0.2 °C. For the correct determination of external mixtures, it is necessary to take into account size-dependent losses due to diffusion in the plumbing between the DMAs and in the aerosol humidification unit.
- ItemHygroscopicity distribution concept for measurement data analysis and modeling of aerosol particle mixing state with regard to hygroscopic growth and CCN activation(München : European Geopyhsical Union, 2010) Su, H.; Rose, D.; Cheng, Y.F.; Gunthe, S.S.; Massling, A.; Stock, M.; Wiedensohler, A.; Andreae, M.O.; Pöschl, U.This paper presents a general concept and mathematical framework of particle hygroscopicity distribution for the analysis and modeling of aerosol hygroscopic growth and cloud condensation nucleus (CCN) activity. The cumulative distribution function of particle hygroscopicity, H(κ, Dd) is defined as the number fraction of particles with a given dry diameter, Dd, and with an effective hygroscopicity parameter smaller than the parameter κ. From hygroscopicity tandem differential mobility analyzer (HTDMA) and size-resolved CCN measurement data, H(κ, Dd) can be derived by solving the κ-Köhler model equation. Alternatively, H(κ, Dd) can be predicted from measurement or model data resolving the chemical composition of single particles. A range of model scenarios are used to explain and illustrate the concept, and exemplary practical applications are shown with HTDMA and CCN measurement data from polluted megacity and pristine rainforest air. Lognormal distribution functions are found to be suitable for approximately describing the hygroscopicity distributions of the investigated atmospheric aerosol samples. For detailed characterization of aerosol hygroscopicity distributions, including externally mixed particles of low hygroscopicity such as freshly emitted soot, we suggest that size-resolved CCN measurements with a wide range and high resolution of water vapor supersaturation and dry particle diameter should be combined with comprehensive HTDMA measurements and size-resolved or single-particle measurements of aerosol chemical composition, including refractory components. In field and laboratory experiments, hygroscopicity distribution data from HTDMA and CCN measurements can complement mixing state information from optical, chemical and volatility-based techniques. Moreover, we propose and intend to use hygrosc
- ItemHygroscopic properties of atmospheric aerosol particles over the Eastern Mediterranean: Implications for regional direct radiative forcing under clean and polluted conditions(München : European Geopyhsical Union, 2011) Stock, M.; Cheng, Y.F.; Birmili, W.; Massling, A.; Wehner, B.; Müller, T.; Leinert, S.; Kalivitis, N.; Mihalopoulos, N.; Wiedensohler, A.This work examines the effect of direct radiative forcing of aerosols in the eastern Mediterranean troposphere as a function of air mass composition, particle size distribution and hygroscopicity, and relative humidity (RH). During intensive field measurements on the island of Crete, Greece, the hygroscopic properties of atmospheric particles were determined using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) and a Hygroscopicity Differential Mobility Analyzer-Aerodynamic Particle Sizer (H-DMA-APS). Similar to former studies, the H-TDMA identified three hygroscopic sub-fractions of particles in the sub-μm range: a more hygroscopic group, a less hygroscopic group and a nearly hydrophobic particle group. The average hygroscopic particle growth factors at 90 % RH were a significant function of particle mobility diameter (Dp): 1.42 (± 0.05) at 30 nm compared to 1.63 (± 0.07) at 250 nm. The H-DMA-APS identified up to three hygroscopic sub-fractions at mobility diameters of 1.0 and 1.2 μm. The data recorded between 12 August and 20 October 2005 were classified into four distinct synoptic-scale air mass types distinguishing between different regions of origin (western Mediterranean vs. the Aegean Sea) as well as the degree of continental pollution (marine vs. continentally influenced). The hygroscopic properties of particles with diameter Dp≥150 nm showed the most pronounced dependency on air mass origin, with growth factors in marine air masses exceeding those in continentally influenced air masses. Particle size distributions and hygroscopic growth factors were used to calculate aerosol light scattering coefficients at ambient RH using a Mie model. A main result was the pronounced enhancement of particle scattering over the eastern Mediterranean due to hygroscopic growth, both in the marine and continentally influenced air masses. When RH reached its summer daytime values around 70–80 %, up to 50–70 % of the calculated visibility reduction was due to the hygroscopic growth of the particles by water compared to the effect of the dry particles alone. The estimated aerosol direct radiative forcings for both, marine and continentally influenced air masses were negative indicating a net cooling of the atmosphere due to the aerosol. The radiative forcing ΔFr was nevertheless governed by the total aerosol concentration most of the time: ΔFr was typically more negative for continentally influenced aerosols (ca. −4 W m−2) compared to rather clean marine aerosols (ca. −1.5 W m−2). When RH occasionally reached 90 % in marine air masses, ΔFr even reached values down to −7 W m−2. Our results emphasize, on the basis of explicit particle hygroscopicity measurements, the relevance of ambient RH for the radiative forcing of regional atmospheres.
- ItemWater uptake by biomass burning aerosol at sub- and supersaturated conditions: closure studies and implications for the role of organics(München : European Geopyhsical Union, 2011) Dusek, U.; Frank, G.P.; Massling, A.; Zeromskiene, K.; Iinuma, Y.; Schmid, O.; Helas, G.; Hennig, T.; Wiedensohler, A.; Andreae, M.O.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.
- ItemHygroscopic growth of sub-micrometer and one-micrometer aerosol particles measured during ACE-Asia(München : European Geopyhsical Union, 2007) Massling, A.; Leinert, S.; Wiedensohler, A.; Covert, D.Hygroscopic properties of aerosol particles in the sub-micrometer and one-micrometer size ranges were measured during the ACE-Asia study (Aerosol Characterization Experiment-Asia) in spring 2001. The measurements took place off the coasts of Japan, Korea, and China. All instruments contributing to this study were deployed in a container on the forward deck of the NOAA Research Vessel Ronald H. Brown. Air masses with primarily marine influence and air masses from the Asian continent affected by both anthropogenic sources and by the transport of desert dust aerosol were encountered during the cruise. Results showed very different hygroscopic behavior in the sub-micrometer size range compared to the one-micrometer size range. In general, for all continentally influenced air masses, the one-micrometer particle population was characterized by two different particle groups – a nearly hydrophobic fraction with growth factors around 1.0 representative of dust particles and a sea salt fraction with hygroscopic growth factors around 2.0. The number fraction of dust particles was generally about 60% independent of long-range air mass origin. For sub-micrometer particles, a dominant, more hygroscopic particle fraction with growth factors between 1.5 and 1.9 (depending on dry particle size) consistent with ammonium sulfate or non-neutralized sulfates as major component was always found. In marine air masses and for larger sizes within the sub-micrometer range (Dp=250 and 350 nm), a sea salt fraction with growth factors between 2.0 and 2.1 was also observed. For all other air masses, the more hygroscopic particle fraction in the sub-micrometer size range was mostly accompanied by a less hygroscopic particle fraction with growth factors between 1.20 and 1.55 depending on both the continental sources and the dry particle size. Number fractions of this particle group varied between 4 and 39% depending on dry particle size and air mass type. Nearly hydrophobic particles indicating dust particles in the sub-micrometer size regime were only found for particles with Dp=250 and 350 nm during a time period when the aerosol was influenced by transport from Asian desert regions.
- ItemHygroscopic growth of urban aerosol particles in Beijing (China) during wintertime: A comparison of three experimental methods(München : European Geopyhsical Union, 2009) Meier, J.; Wehner, B.; Massling, A.; Birmili, W.; Nowak, A.; Gnauk, T.; Brüggemann, E.; Herrmann, H.; Min, H.; Wiedensohler, A.The hygroscopic properties of atmospheric aerosols are highly relevant for the quantification of radiative effects in the atmosphere, but also of interest for the assessment of particle health effects upon inhalation. This article reports measurements of aerosol particle hygroscopicity in the highly polluted urban atmosphere of Beijing, China in January 2005. The meteorological conditions corresponded to a relatively cold and dry atmosphere. Three different methods were used: 1) A combination of Humidifying Differential Mobility Particle Sizer (H-DMPS) and Twin Differential Mobility Particle Sizer (TDMPS) measurements, 2) A Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA), and 3) A simplistic solubility model fed by chemical particle composition determined from Micro Orifice Uniform Deposit Impactor (MOUDI) samples. From the H-DMPS and TDMPS particle number size distributions, a size-resolved descriptive hygroscopic growth factor (DHGF) was determined for the relative humidities (RH) 55%, 77% and 90%, and particle diameters between 30 and 400 nm. In Beijing, the highest DHGFs were observed for accumulation mode particles, 1.40 (±0.03) at 90% RH. DHGF decreased significantly with particle size, reaching 1.04 (±0.15) at 30 nm. H-TDMA data also suggest a decrease in growth factor towards the biggest particles investigated (350 nm), associated with an increasing fraction of nearly hydrophobic particles. The agreement between the H-DMPS/TDMPS and H-TDMA methods was satisfactory in the accumulation mode size range (100–400 nm). In the Aitken mode range (<100 nm), the H-DMPS/TDMPS method yielded growth factors lower by up to 0.1 at 90% RH. The application of the solubility model based on measured chemical composition clearly reproduced the size-dependent trend in hygroscopic particle growth observed by the other methods. In the case of aerosol dominated by inorganic ions, the composition-derived growth factors tended to agree (± 0.05) or underestimate (up to 0.1) the values measured by the other two methods. In the case of aerosol dominated by organics, the reverse was true, with an overestimation of up to 0.2. The results shed light on the experimental and methodological uncertainties that are still connected with the determination of hygroscopic growth factors.
- ItemParticle size distributions in the Eastern Mediterranean troposphere(München : European Geopyhsical Union, 2008) Kalivitis, N.; Birmili, W.; Stock, M.; Wehner, B.; Massling, A.; Wiedensohler, A.; Gerasopoulos, E.; Mihalopoulos, N.Atmospheric particle size distributions were measured on Crete island, Greece in the Eastern Mediterranean during an intensive field campaign between 28 August and 20 October, 2005. Our instrumentation combined a differential mobility particle sizer (DMPS) and an aerodynamic particle sizer (APS) and measured number size distributions in the size range 0.018 μm–10 μm. Four time periods with distinct aerosol characteristics were discriminated, two corresponding to marine and polluted air masses, respectively. In marine air, the sub-μm size distributions showed two particle modes centered at 67 nm and 195 nm having total number concentrations between 900 and 2000 cm−3. In polluted air masses, the size distributions were mainly unimodal with a mode typically centered at 140 nm, with number concentrations varying between 1800 and 2900 cm−3. Super-μm particles showed number concentrations in the range from 0.01 to 2.5 cm−3 without any clear relation to air mass origin. A small number of short-lived particle nucleation events were recorded, where the calculated particle formation rates ranged between 1.1–1.7 cm−3 s−1. However, no particle nucleation and growth events comparable to those typical for the continental boundary layer were observed. Particles concentrations (Diameter <50 nm) were low compared to continental boundary layer conditions with an average concentration of 300 cm−3. The production of sulfuric acid and its subsequently condensation on preexisting particles was examined with the use of a simplistic box model. These calculations suggested that the day-time evolution of the Aitken particle population was governed mainly by coagulation and that particle formation was absent during most days.
- ItemNew particle formation in the Front Range of the Colorado Rocky Mountains(München : European Geopyhsical Union, 2008) Boy, M.; Karl, T.; Turnipseed, A.; Mauldin, R.L.; Kosciuch, E.; Greenberg, J.; Massling, A.; Rathbone, J.; Smith, J.; Held, A.; Barsanti, K.; Wehner, B.; Bauer, S.; Wiedensohler, A.; Bonn, B.; Kulmala, M.; Guenther, A.New particle formation is of interest because of its influence on the properties of aerosol population, and due to the possible contribution of newly formed particles to cloud condensation nuclei. Currently no conclusive evidence exists as to the mechanism or mechanisms of nucleation and subsequent particle growth. However, nucleation rates exhibit a clear dependence on ambient sulphuric acid concentrations and particle growth is often attributed to the condensation of organic vapours. A detailed study of new particle formation in the Front Range of the Colorado Rocky Mountains is presented here. Gas and particle measurement data for 32 days was analyzed to identify event days, possible event days, and non-event days. A detailed analysis of nucleation and growth is provided for four days on which new particle formation was clearly observed. Evidence for the role of sesquiterpenes in new particle formation is presented.
- ItemSize distribution, mass concentration, chemical and mineralogical composition and derived optical parameters of the boundary layer aerosol at Tinfou, Morocco, during SAMUM 2006(Milton Park : Taylor & Francis, 2017) Kandler, K.; Schütz, L.; Deutscher, C.; Ebert, M.; Hofmann, H.; Jäckel, S.; Jaenicke, R.; Knippertz, P.; Lieke, K.; Massling, A.; Petzold, A.; Schladitz, A.; Weinzierl, B.; Wiedensohler, A.; Zorn, S.; Weinbruch, S.During the SAMUM 2006 field campaign in southern Morocco, physical and chemical properties of desert aerosols were measured. Mass concentrations ranging from 30μgm−3 for PM2.5 under desert background conditions up to 300 000μgm−3 for total suspended particles (TSP) during moderate dust storms were measured. TSP dust concentrations are correlated with the local wind speed, whereasPM10 andPM2.5 concentrations are determined by advection from distant sources. Size distributions were measured for particles with diameter between 20 nm and 500μm (parametrizations are given). Two major regimes of the size spectrum can be distinguished. For particles smaller than 500 nm diameter, the distributions show maxima around 80 nm, widely unaffected of varying meteorological and dust emission conditions. For particles larger than 500 nm, the range of variation may be up to one order of magnitude and up to three orders of magnitude for particles larger than 10μm. The mineralogical composition of aerosol bulk samples was measured by X-ray powder diffraction. Major constituents of the aerosol are quartz, potassium feldspar, plagioclase, calcite, hematite and the clay minerals illite, kaolinite and chlorite. A small temporal variability of the bulk mineralogical composition was encountered. The chemical composition of approximately 74 000 particles was determined by electron microscopic single particle analysis. Three size regimes are identified: for smaller than 500 nm in diameter, the aerosol consists of sulphates and mineral dust. For larger than 500 nm up to 50μm, mineral dust dominates, consisting mainly of silicates, and—to a lesser extent—carbonates and quartz. For diameters larger than 50μm, approximately half of the particles consist of quartz. Time series of the elemental composition show a moderate temporal variability of the major compounds. Calcium-dominated particles are enhanced during advection from a prominent dust source in Northern Africa (Chott El Djerid and surroundings). The particle aspect ratio was measured for all analysed particles. Its size dependence reflects that of the chemical composition. For larger than 500 nm particle diameter, a median aspect ratio of 1.6 is measured. Towards smaller particles, it decreases to about 1.3 (parametrizations are given). From the chemical/mineralogical composition, the aerosol complex refractive index was determined for several wavelengths from ultraviolet to near-infrared. Both real and imaginary parts show lower values for particles smaller than 500 nm in diameter (1.55–2.8 × 10−3i at 530 nm) and slightly higher values for larger particles (1.57–3.7 × 10−3i at 530 nm).
- ItemHygroscopic properties of submicrometer atmospheric aerosol particles measured with H-TDMA instruments in various environments - A review(Milton Park : Taylor & Francis, 2017) Swietlicki, E.; Hansson, H.-C.; Hämeri, K.; Svenningsson, B.; Massling, A.; Mcfiggans, G.; Mcmurry, P.H.; Petäjä, T.; Tunved, P.; Gysel, M.; Topping, D.; Weingartner, E.; Baltensperger, U.; Rissler, J.; Wiedensohler, A.; Kulmala, M.The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the sizeresolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth.