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- ItemCloud phase identification of Arctic boundary-layer clouds from airborne spectral reflection measurements: Test of three approaches(München : European Geopyhsical Union, 2008) Ehrlich, A.; Bierwirth, E.; Wendisch, M.; Gayet, J.-F.; Mioche, G.; Lampert, A.; Heintzenberg, J.Arctic boundary-layer clouds were investigated with remote sensing and in situ instruments during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. The clouds formed in a cold air outbreak over the open Greenland Sea. Beside the predominant mixed-phase clouds pure liquid water and ice clouds were observed. Utilizing measurements of solar radiation reflected by the clouds three methods to retrieve the thermodynamic phase of the cloud are introduced and compared. Two ice indices IS and IP were obtained by analyzing the spectral pattern of the cloud top reflectance in the near infrared (1500–1800 nm wavelength) spectral range which is characterized by ice and water absorption. While IS analyzes the spectral slope of the reflectance in this wavelength range, IS utilizes a principle component analysis (PCA) of the spectral reflectance. A third ice index IA is based on the different side scattering of spherical liquid water particles and nonspherical ice crystals which was recorded in simultaneous measurements of spectral cloud albedo and reflectance. Radiative transfer simulations show that IS, IP and IA range between 5 to 80, 0 to 8 and 1 to 1.25 respectively with lowest values indicating pure liquid water clouds and highest values pure ice clouds. The spectral slope ice index IS and the PCA ice index IP are found to be strongly sensitive to the effective diameter of the ice crystals present in the cloud. Therefore, the identification of mixed-phase clouds requires a priori knowledge of the ice crystal dimension. The reflectance-albedo ice index IA is mainly dominated by the uppermost cloud layer (τ<1.5). Therefore, typical boundary-layer mixed-phase clouds with a liquid cloud top layer will be identified as pure liquid water clouds. All three methods were applied to measurements above a cloud field observed during ASTAR 2007. The comparison with independent in situ microphysical measurements shows the ability of the three approaches to identify the ice phase in Arctic boundary-layer clouds.
- ItemOrigin of aerosol particles in the mid-latitude and subtropical upper troposphere and lowermost stratosphere from cluster analysis of CARIBIC data(München : European Geopyhsical Union, 2009) Köppe, M.; Hermann, M.; Brenninkmeijer, C.A.M.; Heintzenberg, J.; Schlager, H.; Schuck, T.; Slemr, F.; Sprung, D.; van Velthoven, P.F.J.; Wiedensohler, A.; Zahn, A.; Ziereis, H.The origin of aerosol particles in the upper troposphere and lowermost stratosphere over the Eurasian continent was investigated by applying cluster analysis methods to in situ measured data. Number concentrations of submicrometer aerosol particles and trace gas mixing ratios derived by the CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container) measurement system on flights between Germany and South-East Asia were used for this analysis. Four cluster analysis methods were applied to a test data set and their capability of separating the data points into scientifically reasonable clusters was assessed. The best method was applied to seasonal data subsets for summer and winter resulting in five cluster or air mass types: stratosphere, tropopause, free troposphere, high clouds, and boundary layer influenced. Other source clusters, like aircraft emissions could not be resolved in the present data set with the used methods. While the cluster separation works satisfactory well for the summer data, in winter interpretation is more difficult, which is attributed to either different vertical transport pathways or different chemical lifetimes in both seasons. The geographical distribution of the clusters together with histograms for nucleation and Aitken mode particles within each cluster are presented. Aitken mode particle number concentrations show a clear vertical gradient with the lowest values in the lowermost stratosphere (750–2820 particles/cm3 STP, minimum of the two 25% – and maximum of the two 75%-percentiles of both seasons) and the highest values for the boundary-layer-influenced air (4290–22 760 particles/cm3 STP). Nucleation mode particles are also highest in the boundary-layer-influenced air (1260–29 500 particles/cm3 STP), but are lowest in the free troposphere (0–450 particles/cm3 STP). The given submicrometer particle number concentrations represent the first large-scale seasonal data sets for the upper troposphere and lowermost stratosphere over the Eurasian continent.
- ItemTraffic restrictions in Beijing during the Sino-African Summit 2006: Aerosol size distribution and visibility compared to long-term in situ observations(München : European Geopyhsical Union, 2008) Cheng, Y.F.; Heintzenberg, J.; Wehner, B.; Wu, Z.J.; Su, H.; Mao, J.T.Based on the long-term in-situ observations of aerosol particle number size distributions and meteorological parameters, the measures of traffic restriction during the Sino-African Summit (4–6 November 2006) in Beijing, China have been found to be efficient in reducing the number concentration of aerosol particles, in particular Aitken and accumulation mode particles, and in improving the visibility when local emissions dominated. The influence of traffic restrictions on the particle concentrations differed for different particle sizes. More significant effects on fine particles with diameters ranging from 40 to 500 nm have been found. Based on statistical analysis of long-term observations, under comparable weather conditions, the number concentrations of the particles in Aitken and accumulation modes seemingly were reduced by 20–60% when the traffic restrictions were in place. This change may be mainly due to the reduction of secondary particle contributions. However, it is worth to notice that the reduction of 60% might overestimate the effect of the measures of traffic control, due to the inherent data shortage with very high wind speeds in the comparison data population. Our size-dependent aerosol data also indicate that measures led to reductions in particulate air pollution in the optically most important diameter range, whereas further vehicle restriction measures might lead to an increase in ultrafine particle formation if the condensational sink further decreased. Assuming that there were no traffic restrictions and with normal levels of the vehicle emissions, the visibilities during the Summit would have been lower by about 20–45%. The fact that over 95% cases with visibility range lower than 5 km during 2004 to 2007 occurred when the local wind speed was lower than 3 m s−1 may suggest that the importance of the emission restrictions is highest when the wind speed is lower than 3 m s−1, concerning the improvement of serious low visibility situations in Beijing.
- ItemSO2 oxidation products other than H2SO4 as a trigger of new particle formation. Part 1: Laboratory investigations(München : European Geopyhsical Union, 2008) Berndt, T.; Stratmann, F.; Bräsel, S.; Heintzenberg, J.; Laaksonen, A.; Kulmala, M.Mechanistic investigations of atmospheric H2SO4 particle formation have been performed in a laboratory study taking either H2SO4 from a liquid reservoir or using the gas-phase reaction of OH radicals with SO2. Applying both approaches for H2SO4 generation simultaneously it was found that H2SO4 evaporated from the liquid reservoir acts considerably less effective for the process of particle formation and growth than the products originating from the reaction of OH radicals with SO2. Furthermore, for NOx concentrations >5×1011 molecule cm−3 the formation of new particles from the reaction of OH radicals with SO2 is inhibited. This suggests that substances other than H2SO4 (potentially products from sulphur-containing peroxy radicals) trigger lower tropospheric new particle formation and growth. The currently accepted mechanism for SO2 gas-phase oxidation does not consider the formation of such substances. The analysis of new particle formation for different reaction conditions in our experiment suggests that a contribution of impurities to the nucleation process is unlikely.
- ItemEvaluation of a global aerosol microphysics model against size-resolved particle statistics in the marine atmosphere(München : European Geopyhsical Union, 2007) Spracklen, D.V.; Pringle, K.J.; Carslaw, K.S.; Mann, G.W.; Manktelow, P.; Heintzenberg, J.A statistical synthesis of marine aerosol measurements from experiments in four different oceans is used to evaluate a global aerosol microphysics model (GLOMAP). We compare the model against observed size resolved particle concentrations, probability distributions, and the temporal persistence of different size particles. We attempt to explain the observed sub-micrometre size distributions in terms of sulfate and sea spray and quantify the possible contributions of anthropogenic sulfate and carbonaceous material to the number and mass distribution. The model predicts a bimodal size distribution that agrees well with observations as a grand average over all regions, but there are large regional differences. Notably, observed Aitken mode number concentrations are more than a factor 10 higher than in the model for the N Atlantic but a factor 7 lower than the model in the NW Pacific. We also find that modelled Aitken mode and accumulation mode geometric mean diameters are generally smaller in the model by 10–30%. Comparison with observed free tropospheric Aitken mode distributions suggests that the model underpredicts growth of these particles during descent to the marine boundary layer (MBL). Recent observations of a substantial organic component of free tropospheric aerosol could explain this discrepancy. We find that anthropogenic continental material makes a substantial contribution to N Atlantic MBL aerosol, with typically 60–90% of sulfate across the particle size range coming from anthropogenic sources, even if we analyse air that has spent an average of >120 h away from land. However, anthropogenic primary black carbon and organic carbon particles (at the emission size and quantity assumed here) do not explain the large discrepancies in Aitken mode number. Several explanations for the discrepancy are suggested. The lack of lower atmospheric particle formation in the model may explain low N Atlantic particle concentrations. However, the observed and modelled particle persistence at Cape Grim in the Southern Ocean, does not reveal a diurnal cycle consistent with a photochemically driven local particle source. We also show that a physically based cloud drop activation scheme better explains the observed change in accumulation mode geometric mean diameter with particle number.
- ItemNew-particle formation events in a continental boundary layer: First results from the SATURN experiment(München : European Geopyhsical Union, 2003) Stratmann, F.; Siebert, H.; Spindler, G.; Wehner, B.; Althausen, D.; Heintzenberg, J.; Hellmuth, O.; Rinke, R.; Schmieder, U.; Seidel, C.; Tuch, T.; Uhrner, U.; Wiedensohler, A.; Wandinger, U.; Wendisch, M.; Schell, D.; Stohl, A.During the SATURN experiment, which took place from 27 May to 14 June 2002, new particle formation in the continental boundary layer was investigated. Simultaneous ground-based and tethered-balloon-borne measurements were performed, including meteorological parameters, particle number concentrations and size distributions, gaseous precursor concentrations and SODAR and LIDAR observations. Newly formed particles were observed inside the residual layer, before the break-up process of the nocturnal inversion, and inside the mixing layer throughout the break-up of the nocturnal inversion and during the evolution of the planetary boundary layer.
- ItemCivil Aircraft for the regular investigation of the atmosphere based on an instrumented container: The new CARIBIC system(München : European Geopyhsical Union, 2007) Brenninkmeijer, C.A.M.; Crutzen, P.; Boumard, F.; Dauer, T.; Dix, B.; Ebinghaus, R.; Filippi, D.; Fischer, H.; Franke, H.; Frieß, U.; Heintzenberg, J.; Helleis, F.; Hermann, M.; Kock, H.H.; Koeppel, C.; Lelieveld, J.; Leuenberger, M.; Martinsson, B.G.; Miemczyk, S.; Moret, H.P.; Nguyen, H.N.; Nyfeler, P.; Oram, D.; O'Sullivan, D.; Penkett, S.; Platt, U.; Pupek, M.; Ramonet, M.; Randa, B.; Reichelt, M.; Rhee, T.S.; Rohwer, J.; Rosenfeld, K.; Scharffe, D.; Schlager, H.; Schumann, U.; Slemr, F.; Sprung, D.; Stock, P.; Thaler, R.; Valentino, F.; van Velthoven, P.; Waibel, A.; Wandel, A.; Waschitschek, K.; Wiedensohler, A.; Xueref-Remy, I.; Zahn, A.; Zech, U.; Ziereis, H.An airfreight container with automated instruments for measurement of atmospheric gases and trace compounds was operated on a monthly basis onboard a Boeing 767-300 ER of LTU International Airways during long-distance flights from 1997 to 2002 (CARIBIC, Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container, http://www.caribic-atmospheric.com). Subsequently a more advanced system has been developed, using a larger capacity container with additional equipment and an improved inlet system. CARIBIC phase #2 was implemented on a new long-range aircraft type Airbus A340-600 of the Lufthansa German Airlines (Star Alliance) in December 2004, creating a powerful flying observatory. The instrument package comprises detectors for the measurement of O3, total and gaseous H2O, NO and NOy, CO, CO2, O2, Hg, and number concentrations of sub-micrometer particles (>4 nm, >12 nm, and >18 nm diameter). Furthermore, an optical particle counter (OPC) and a proton transfer mass spectrometer (PTR-MS) are incorporated. Aerosol samples are collected for analysis of elemental composition and particle morphology after flight. Air samples are taken in glass containers for laboratory analyses of hydrocarbons, halocarbons and greenhouse gases (including isotopic composition of CO2) in several laboratories. Absorption tubes collect oxygenated volatile organic compounds. Three differential optical absorption spectrometers (DOAS) with their telescopes mounted in the inlet system measure atmospheric trace gases such as BrO, HONO, and NO2. A video camera mounted in the inlet provides information about clouds along the flight track. The flying observatory, its equipment and examples of measurement results are reported.
- ItemLACIS-measurements and parameterization of sea-salt particle hygroscopic growth and activation(München : European Geopyhsical Union, 2008) Niedermeier, D.; Wex, H.; Voigtländer, J.; Stratmann, F.; Brüggemann, E.; Kiselev, A.; Henk, H.; Heintzenberg, J.The Leipzig Aerosol Cloud Interaction Simulator (LACIS) was used to investigate the hygroscopic growth and activation of sea-salt particles which were generated from three different sea-water samples. The measurements showed that the sea-salt particles exhibit a slightly reduced hygroscopic growth compared to pure NaCl particles. Köhler theory was utilized to model the hygroscopic growth of these particles. Some parameters used in this model are unknown for sea-salt. These parameters are combined in an "ionic density" ρion. For each sea-salt sample an average ρion was determined by fitting the Köhler equation to the data from the hygroscopic growth measurements. LACIS was also used to measure the activation of the sea-salt particles at three different supersaturations: 0.11%, 0.17% and 0.32%. A CCN-closure was tested by calculating the critical diameters Dcrit for the sea-salt particles at these supersaturations, using the Köhler model and the corresponding ρion as derived from the hygroscopic growth data. These calculated critical diameters were compared to the measured ones. Measured and calculated values of Dcrit agree within the level of uncertainty. Based on this successful closure, a new parameterization to describe sea-salt-particle hygroscopic growth (at RH>95%) and activation has been developed.
- ItemOut of Africa: High aerosol concentrations in the upper troposphere over Africa(München : European Geopyhsical Union, 2003) Heintzenberg, J.; Hermann, M.; Theiss, D.In the year 2000, six flights (three southbound and three northbound) of the CARIBIC project were conducted between Germany and two destinations in the southern hemisphere (Windhoek, Namibia and Cape Town, South Africa). In the present report, results on particle number concentrations are discussed in three size ranges (>4 nm, >12 nm, and >18 nm particle diameter) during the unique transequatorial Africa flights. The flights covered a total of about 80 h in May, July, and December. Thus, no claim can be made for long-term representativeness of the aerosol data. Nevertheless, they are the first upper systematic tropospheric transequatorial aerosol profiles over Africa. The average aerosol results show a broad maximum, roughly symmetrical to the equator, which compares well in latitudinal extent to a maximum of CO concentrations measured on the same flights. This export of continental surface aerosol to the upper troposphere will be dispersed on a global scale both with the easterly flow near the equator and with the westerlies in the adjacent subtropical regions. There was strong evidence of recent new particle formation before aerosol arrival at flight level, in particular during the time periods between 9:00 and 13:00 local time over Africa. Direct and indirect climate effects of the respective particulate matter remain to be investigated by future flights with the ongoing extension of the CARIBIC payload towards size-resolved measurements above 100 nm particle diameter. At the same time global chemical transport models and aerosol dynamics models need to be extended to be able to reproduce the CARIBIC findings over Africa.