13-month climatology of the aerosol hygroscopicity at the free tropospheric site Jungfraujoch (3580 m a.s.l.)

A hygroscopicity tandem differential mobility analyzer (HTDMA) was operated at the high-alpine site Jungfraujoch in order to characterize the hygroscopic diameter growth factors of the free tropospheric Aitken and accumulation mode aerosol. More than ~5000 h of valid data were collected for the dry diameters <i>D</i><sub>0</sub> = 35, 50, 75, 110, 165, and 265 nm during the 13-month measurement period from 1 May 2008 through 31 May 2009. No distinct seasonal variability of the hygroscopic properties was observed. Annual mean hygroscopic diameter growth factors (<i>D</i>/<i>D</i><sub>0</sub>) at 90% relative humidity were found to be 1.34, 1.43, and 1.46 for <i>D</i><sub>0</sub> = 50, 110, and 265 nm, respectively. This size dependence can largely be attributed to the Kelvin effect because corresponding values of the hygroscopicity parameter κ are nearly independent of size. The mean hygroscopicity of the Aitken and accumulation mode aerosol at the free tropospheric site Jungfraujoch was found to be κ≈0.24 with little variability throughout the year. <br><br> The impact of Saharan dust events, a frequent phenomenon at the Jungfraujoch, on aerosol hygroscopicity was shown to be negligible for <i>D</i><sub>0</sub><265 nm. Thermally driven injections of planetary boundary layer (PBL) air, particularly observed in the early afternoon of summer days with convective anticyclonic weather conditions, lead to a decrease of aerosol hygroscopicity. However, the effect of PBL influence is not seen in the annual mean hygroscopicity data because the effect is small and those conditions (weather class, season and time of day) with PBL influence are relatively rare. <br><br> Aerosol hygroscopicity was found to be virtually independent of synoptic wind direction during advective weather situations, i.e. when horizontal motion of the atmosphere dominates over thermally driven convection. This indicates that the hygroscopic behavior of the aerosol observed at the Jungfraujoch can be considered representative of the lower free troposphere on at least a regional if not continental scale

Measured and predicted aerosol light scattering enhancement factors at the high alpine site Jungfraujoch

Ambient relative humidity (RH) determines the water content of atmospheric aerosol particles and thus has an important influence on the amount of visible light scattered by particles. The RH dependence of the particle light scattering coefficient (σ<sub>sp</sub>) is therefore an important variable for climate forcing calculations. We used a humidification system for a nephelometer which allows for the measurement of σ<sub>sp</sub> at a defined RH in the range of 20–95%. In this paper we present measurements of light scattering enhancement factors <i>f</i>(RH)=σ<sub>sp</sub>(RH)/σ<sub>sp</sub>(dry) from a 1-month campaign (May 2008) at the high alpine site Jungfraujoch (3580 m a.s.l.), Switzerland. Measurements at the Jungfraujoch are representative for the lower free troposphere above Central Europe. For this aerosol type hardly any information about the <i>f</i>(RH) is available so far. At this site, <i>f</i>(RH=85%) varied between 1.2 and 3.3. Measured <i>f</i>(RH) agreed well with <i>f</i>(RH) calculated with Mie theory using measurements of the size distribution, chemical composition and hygroscopic diameter growth factors as input. Good <i>f</i>(RH) predictions at RH<85% were also obtained with a simplified model, which uses the Ångström exponent of σ<sub>sp</sub>(dry) as input. RH influences further intensive optical aerosol properties. The backscatter fraction decreased by about 30% from 0.128 to 0.089, and the single scattering albedo increased on average by 0.05 at 85% RH compared to dry conditions. These changes in σ<sub>sp</sub>, backscatter fraction and single scattering albedo have a distinct impact on the radiative forcing of the Jungfraujoch aerosol

Intercomparison Study of Six HTDMAs: Results and Recommendations

We report on an intercomparison of six different hygroscopicity tandem differential mobility analysers (HTDMAs). These HTDMAs are used worldwide in laboratory experiments and field campaigns to measure the water uptake of aerosol particles and have never been intercompared. After an investigation of the different design of the instruments with their advantages and inconveniencies, the methods for calibration, validation and data analysis are presented. Measurements of nebulised ammonium sulphate as well as of secondary organic aerosol generated from a smog chamber were performed. Agreement and discrepancies between the instruments and to the theory are discussed, and final recommendations for a standard instrument are given, as a benchmark for laboratory or field experiments to ensure a high quality of HTDMA data.JRC.H.2-Climate chang

Quantity increase and functional affinity/avidity decrease of anti-FcεRI and anti-IgE autoantibodies in chronic spontaneous urticaria.

Background. Patients with autoimmune forms of chronic spontaneous urticaria (aiCSU) exhibit autoantibodies against the high-affinity IgE receptor (FcεRI) and IgE. As the presence of these autoantibodies does not correlate with disease activity, the functional affinity/avidity may be relevant in aiCSU. This exploratory study aimed to characterize the quantity and avidity of autoantibodies against IgE and FcεRI over 6 months. Methods. The serum of 49 patients with CSU and 30 healthy control subjects was obtained at baseline and 6 months. Serum was analyzed by ELISA, to determine the quantity and avidity of anti-IgE and anti-FcεRI autoantibodies, and by basophil activation test (CU-BAT). Results. An increase in the quantity of anti-FcεRI and anti-IgE antibodies and a simultaneous decrease in avidity was found in all patients with CSU after 6 months: median anti-IgE increased from 6.7 ng/mL (IQR 5.1-12.5) to 23.8 ng/mL (IQR 12.3-121.5), p less than 0.001, median anti-FcεRI from 52.4 ng/mL (IQR 26.3-111.4) to 129.5 ng/mL (IQR 73.7-253.7), p less than 0.001. Median anti-IgE avidity decreased from 75.8% (IQR 55.3-90.8) to 56.4% (IQR 30.6-76.2), p=0.019 and median anti-FcεRI avidity from 75.1% (IQR 49.8-90.0) to 52.2 (IQR 38.2-60.1), p less than 0.001. In contrast, the frequency of activated basophils did not change significantly over time. Surprisingly, autoantibody avidity did not correlate with basophil activation. Conclusions. Both the quantity and avidity of anti-FcεRI and anti-IgE antibodies change over time, demonstrating that the CU-BAT is more suitable to diagnose aiCSU. In addition, the avidity of anti-FcεRI and anti-IgE antibodies do not correlate with CU-BAT and disease activity, suggesting that further factors independent of anti-FcεRI and anti-IgE autoantibodies contribute to aiCSU

Buurtzorg Project Nijmegen

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A 17 month climatology of the cloud condensation nuclei number concentration at the high alpine site Jungfraujoch

Between May 2008 and September 2009 the cloud condensation nuclei (CCN) number concentration, N-CCN, was measured at the high alpine site Jungfraujoch, which is located in the free troposphere most of the time. Measurements at 10 different supersaturations (0.12%-1.18%) were made using a CCN counter (CCNC). The monthly median NCCN values show a distinct seasonal variability with similar to 5-12 times higher values in summer than in winter. The major part of this variation can be explained by the seasonal amplitude of total aerosol number concentration (similar to 4.5 times higher values in summer), but it is further amplified (factor of similar to 1.1-2.6) by a shift of the particle number size distribution toward slightly larger sizes in summer. In contrast to the extensive properties, the monthly median of the critical dry diameter, above which the aerosols activate as CCN, does not show a seasonal cycle (relative standard deviations of the monthly median critical dry diameters at the different supersaturations are 4-9%) or substantial variability (relative standard deviations of individual data points at the different supersaturations are less than 18-37%). The mean CCN-derived hygroscopicity of the aerosol corresponds to a value of the hygroscopicity parameter k of 0.20 (assuming a surface tension of pure water) with moderate supersaturation dependence. NCCN can be reliably predicted throughout the measurement period with knowledge of the above-mentioned averaged k value and highly time-resolved (similar to 5 min) particle number size distribution data. The predicted N-CCN was within 0.74 to 1.29 times the measured value during 80% of the time (94,499 data points in total at 10 different supersaturations)

Intercomparison study of six HTDMAs : results and recommendations

We report on an intercomparison of six different hygroscopicity tandem differential mobility analysers (HTDMAs). These HTDMAs are used worldwide in laboratory experiments and field campaigns to measure the water uptake of aerosol particles and have never been intercompared. After an investigation of the different design of the instruments with their advantages and inconveniencies, the methods for calibration, validation and data analysis are presented. Measurements of nebulised ammonium sulphate as well as of secondary organic aerosol generated from a smog chamber were performed. Agreement and discrepancies between the instruments and to the theory are discussed, and final recommendations for a standard instrument are given, as a benchmark for laboratory or field experiments to ensure a high quality of HTDMA data.Peer reviewe