Auflistung nach Autor:in "Henning, Silvia"

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Aerosol partitioning in natural mixed‐phase clouds
(Wiley, 16.03.2004) Henning, Silvia; Bojinski, Stephan; Diehl, Karoline; Ghan, Steven; Nyeki, Stephan; Weingartner, Ernest; Wurzler, Sabine; Baltensperger, Urs
In situ aerosol and cloud drop microphysical measurements at a high-alpine site are used to investigate aerosol partitioning between cloud and interstitial phases in natural, mid-latitude, mixed-phase clouds. Measurements indicate a decrease in the activated aerosol fraction (FN) for particle diameters dP > 100 nm with cloud temperature from FN ~ 0.54 in summer liquid-phase clouds to FN ~ 0.08 in winter mixed-phase clouds. The latter may be attributed to the Bergeron-Findeisen mechanism whereby ice crystals grow at the expense of liquid water drops, releasing formerly activated aerosols back into the interstitial phase. This provides a means to distinguish the indirect effects of aerosols on drops and ice crystals.
01A - Beitrag in wissenschaftlicher Zeitschrift
Aerosol single particle composition at the Jungfraujoch
(Elsevier, 01/2005) Hinz, Klaus-Peter; Trimborn, Achim; Weingartner, Ernest; Henning, Silvia; Baltensperger, Urs; Spengler, Bernhard
01A - Beitrag in wissenschaftlicher Zeitschrift
Chemical composition of free tropospheric aerosol for PM1 and coarse mode at the high alpine site Jungfraujoch
(Copernicus, 31.01.2008) Cozic, Julie; Verheggen, Bart; Weingartner, Ernest; Crosier, Jonathan; Bower, Keith N.; Flynn, Michael; Coe, Hugh; Henning, Silvia; Steinbacher, Martin; Henne, Stephan; Collaud Coen, Martine; Petzold, Andreas; Baltensperger, Urs
The chemical composition of submicron (fine mode) and supermicron (coarse mode) aerosol particles has been investigated at the Jungfraujoch high alpine research station (3580 m a.s.l., Switzerland) as part of the GAW aerosol monitoring program since 1999. A clear seasonality was observed for all major components throughout the period with low concentrations in winter (predominantly free tropospheric aerosol) and higher concentrations in summer (enhanced vertical transport of boundary layer pollutants). In addition, mass closure was attempted during intensive campaigns in March 2004, February–March 2005 and August 2005. Ionic, carbonaceous and non-refractory components of the aerosol were quantified as well as the PM1 and coarse mode total aerosol mass concentrations. A relatively low conversion factor of 1.8 for organic carbon (OC) to particulate organic matter (OM) was found in winter (February–March 2005). Organics, sulfate, ammonium, and nitrate were the major components of the fine aerosol fraction that were identified, while calcium and nitrate were the only two measured components contributing to the coarse mode. The aerosol mass concentrations for fine and coarse mode aerosol measured during the intensive campaigns were not typical of the long-term seasonality due largely to dynamical differences. Average fine and coarse mode concentrations during the intensive field campaigns were 1.7 μg m−3 and 2.4 μg m−3 in winter and 2.5 μg m−3 and 2.0 μg m−3 in summer, respectively. The mass balance of aerosols showed higher contributions of calcium and nitrate in the coarse mode during Saharan dust events (SDE) than without SDE.
01A - Beitrag in wissenschaftlicher Zeitschrift
Influence of gas-to-particle partitioning on the hygroscopic and droplet activation behaviour of α-pinene secondary organic aerosol
(Royal Society of Chemistry, 05.08.2009) Jurányi, Zsófia; Gysel, Martin; Duplissy, Jonathan; Weingartner, Ernest; Tritscher, Torsten; Dommen, Josef; Henning, Silvia; Ziese, Markus; Kiselev, Alexej; Stratmann, Frank; George, Ingrid; Baltensperger, Urs
Hygroscopic properties of secondary organic aerosol (SOA) formed by photooxidation of different concentrations (10–27 or 220–270 ppb) of α-pinene precursor were investigated at different relative humidities (RH) using a hygroscopicity tandem differential mobility analyzer (HTDMA, RH = 95–97%) and using the mobile version of the Leipzig Aerosol Cloud Interaction Simulator (LACIS-mobile, RH = 98–99.3%). In addition, the cloud condensation nuclei (CCN) activity was measured applying two CCN counters (CCNC). An apparent single-hygroscopicity parameter, κ, of ∼0.09, ∼0.07–0.13, and ∼0.02–0.04 was derived from CCNC, HTDMA and LACIS data, respectively, assuming the surface tension of pure water. Closure between HTDMA and CCNC data was achieved within experimental uncertainty, whereas closure between LACIS and CCNC was only achieved by assuming a concentration-dependent surface tension reduction, consequently resulting in lower CCNC-derived κ values. Comparing different experimental techniques at varying precursor concentrations in more detail reveals further open questions. Varying precursor concentration influences hygroscopic growth factors at subsaturated RH, while it has no effect on the CCN activation. This difference in behaviour might be caused by precursor concentration-dependent surface tension depression or changing droplet solution concentration dependence of the water activity coefficient with varying SOA composition. Furthermore, evidence was found that the SOA might need several seconds to reach the equilibrium growth factor at high RH.
01A - Beitrag in wissenschaftlicher Zeitschrift
Long‐term trend analysis of aerosol variables at the high‐alpine site Jungfraujoch
(Wiley, 13.07.2007) Collaud Coen, Martine; Weingartner, Ernest; Nyeki, Stephan; Cozic, Julie; Henning, Silvia; Verheggen, Bart; Gehrig, Robert; Baltensperger, Urs
This study reports the first long-term trend analysis of aerosol optical measurements at the high-alpine site Jungfraujoch, which started 10.5 years ago. Since the aerosol variables are approximately lognormally distributed, the seasonal Kendall test and Sen's slope estimator were applied as nonparametric methods to detect the long-term trends for each month. The yearly trend was estimated by a least-mean-square fit, and the number of years necessary to detect this trend was calculated. The most significant trend is the increase (4–7% yr−1) in light-scattering coefficients during the September to December period. The light absorption and backscattering coefficients and the aerosol number concentration also show a positive trend during this time of the year. The hemispheric backscattering fraction and the scattering exponent calculated with the smaller wavelengths (450 and 550 nm), which relate to the small aerosol size fraction, decrease except during the summer, whereas the scattering exponent calculated with the larger wavelengths (550 and 700 nm) remains constant. Generally, the summer months at the Jungfraujoch, which are strongly influenced by planetary boundary layer air masses, do not show any long-term trend. The trends determined by least-mean-square fits of the scattering and backscattering coefficients, the hemispheric backscattering fractions, and the scattering exponent are significant, and the number of years necessary to detect them is shorter than 10 years. For these variables, the trends and the slopes estimated by the seasonal Kendall test are therefore confirmed by the least-mean-square fit results.
01A - Beitrag in wissenschaftlicher Zeitschrift
Saharan dust events at the Jungfraujoch. detection by wavelength dependence of the single scattering albedo and first climatology analysis
(Copernicus, 08.12.2004) Collaud Coen, Martine; Weingartner, Ernest; Schaub, D.; Hueglin, Christoph; Corrigan, C.; Henning, Silvia; Schwikowski, Margit; Baltensperger, Urs
Scattering and absorption coefficients have been measured continuously at several wave-lengths since March 2001 at the high altitude site Jungfraujoch (3580ma.s.l.). From these data, the wavelength dependences of the Ångström exponent and particularly of the single scattering albedo are determined. While the exponent of the single scattering albedo usually increases with wavelength, it decreases with wavelength during Saharan dust events (SDE) due to the greater size of the mineral aerosol particles and their different chemical composition. This change in the sign of the single scattering exponent turns out to be a sensitive means for detecting Saharan dust events. The occurrence of SDE detected by this new method was confirmed by visual in-spection of filter colors and by studying long-range back-trajectories. An examination of SDE over a 22-month period shows that SDE are more frequent during the March-June period as well as during October and November. The trajectory analysis indicated a mean traveling time of 96.5h, with the most important source countries situated in the northern and north-western part of the Saharan desert. Most of the SDE do not lead to a detectable increase of the 48-h total suspended particulate matter (TSP) concentration at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the Jungfraujoch is 16µg/m³, which corresponds to an annual mean of 0.8µg/m³ or 24% of TSP.
01A - Beitrag in wissenschaftlicher Zeitschrift
Seasonal variation of water‐soluble ions of the aerosol at the high‐alpine site Jungfraujoch (3580 m asl)
(Wiley, 15.01.2003) Henning, Silvia; Weingartner, Ernest; Schwikowski, Margit; Gäggeler, Heinz W.; Gehrig, Robert; Hinz, Klaus-Peter; Trimborn, Achim; Spengler, Bernhard; Baltensperger, Urs
Within the Global Atmosphere Watch (GAW) Aerosol Program of the World Meteorological Organization (WMO), the aerosol chemical composition has been continuously measured since July 1999 at the Jungfraujoch (JFJ) of which the first 1.5-year data set is presented. Sampling is performed in two size classes (total suspended particles (TSP) and particles with aerodynamic diameters smaller than 1 μm). The filters are analyzed for major ions, which constitute 30% of the total dry aerosol mass collected at this site. As annual mean, a total ion mass concentration of 1.04 μg mˉ³ was observed. Sulfate, ammonium, and nitrate were the major components of the fine aerosol fraction, while calcium and nitrate were two major water-soluble components in the coarse mode. Single particle analysis confirmed the internal mixture of calcium and nitrate in the coarse mode. The total ion mass concentration showed strong seasonal differences, with 1.25, 1.62, 0.70, and 0.25 μg mˉ³ for spring, summer, fall, and winter, respectively. The variability was stronger for sulfate, ammonium, and nitrate than for calcium. The reason for this is believed to be local sources of calcium, which do not require vertical transport, along with Sahara dust episodes, which occur occasionally over the whole year, independent from the season.
01A - Beitrag in wissenschaftlicher Zeitschrift
Simultaneous dry and ambient measurements of aerosol size distributions at the Jungfraujoch
(Stockholm University Press, 01.01.2003) Nessler, R.; Bukowiecki, Nicolas; Henning, Silvia; Weingartner, Ernest; Calpini, Bertrand; Baltensperger, Urs
In a field campaign at the high-alpine site Jungfraujoch (JFJ, 3580 m asl), in-situ aerosol size distributions were measured simultaneously outdoor at ambient conditions (temperature T < -5 °C) and indoor at dry conditions (T ≈ 25 °C and relative humidity RH < 10%) by means of two scanning mobility particle sizers (SMPS). In addition, measurements of hygroscopic growth factors were performed with a hygroscopicity tandem differential mobility analyzer (H-TDMA). The measured growth factors, being a monotonic function of the relative humidity (RH), were fitted with a modified Köhler model. A comparison between dry and ambient size distributions shows two main features: First, the dry total number concentration is often considerably smaller (on average 28%) than the ambient total number concentration, and is most likely due to the evaporation of volatile material at the higher temperature. These particle losses mainly concern small particles (dry diameter D ≲ 100 nm), and therefore have only a minimal affect on the surface and volume concentrations. A slight correlation between ambient RH and the magnitude of particle loss was observed, but it was not possible to establish an empirical model for a quantification. Second, the dry number size distribution is shifted towards smaller particles, reflecting the hygroscopic behavior of the aerosols. To link the ambient and the dry size distributions we modeled this shift using the H-TDMA measurements and a modified Köhler model. The corrected dry surface and volume concentrations are in good agreement with the ambient measurements for the whole RH range, but the correction works best for RH < 80%. The results indicate that size distribution data measured at indoor conditions (i.e. dry and warm) may be successfully corrected to reflect ambient conditions, which are relevant for determining the impact of aerosol on climate.
01A - Beitrag in wissenschaftlicher Zeitschrift
Size-dependent aerosol activation at the high-alpine site Jungfraujoch (3580 m asl)
(Stockholm University Press, 01.01.2002) Henning, Silvia; Weingartner, Ernest; Schmidt, Sebastian; Wendisch, Manfred; Gäggeler, Heinz W.; Baltensperger, Urs
Microphysical and chemical aerosol properties and their influence on cloud formation were studied in a field campaign at the high-alpine site Jungfraujoch (JFJ, 3580 m asl). Due to its altitude, this site is suitable for ground-based in-cloud measurements, with a high cloud frequency of 40%. Dry total and interstitial aerosol size distributions [18 nm 0.15 g mˉ³. Below this value, D50 increased with decreasing LWC. A dependence of D50 on the accumulation mode (Dp>100 nm) number concentration (Ntot,Dp>100) was only found for concentrations less than 100 cmˉ³. For higher values of Ntot,Dp>100 the D50 remained constant. Furthermore, a decrease of the effective radius of cloud droplets (Reff) with increasing Ntot,Dp>100 was observed, providing experimental evidence for the microphysical relation predicted by the Twomey effect. A modified Köhler model was used to quantify the critical supersaturation for the aerosol observed at the JFJ. Ambient supersaturations were determined from the derived supersaturation curve and the calculated D50. As an example, a critical supersaturation of 0.2% was found for 100 nm particles.
01A - Beitrag in wissenschaftlicher Zeitschrift