Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6)

Abstract

Abstract. Two different single particle mass spectrometers were operated in parallel at the Swiss High Alpine Research Station Jungfraujoch (JFJ, 3580 m a.s.l.) during the Cloud and Aerosol Characterization Experiment (CLACE 6) in February and March 2007. During mixed phase cloud events ice crystals from 5-20 µm were separated from larger ice aggregates, non-activated, interstitial aerosol particles and supercooled droplets using an Ice-Counterflow Virtual Impactor (Ice-CVI). During one cloud period supercooled droplets were additionally sampled and analyzed by changing the Ice-CVI setup. The small ice particles and droplets were evaporated by injection into dry air inside the Ice-CVI. The resulting ice and droplet residues (IR and DR) were analyzed for size and composition by the two single particle mass spectrometers: a custom-built Single Particle Laser-Ablation Time-of-Flight Mass Spectrometer (SPLAT) and a commercial Aerosol Time-of-Flight Mass Spectrometer (ATOFMS, TSI Model 3800). During CLACE 6 the SPLAT instrument characterized 355 individual IR that produced a mass spectrum for at least one polarity and the ATOFMS measured 152 IR. The mass spectra were binned Correspondence to: J. Curtius (curtius@iau.uni-frankfurt.de) in classes, based on the combination of dominating substances, such as mineral dust, sulfate, potassium and elemental carbon or organic material. The derived chemical information from the ice residues is compared to the JFJ ambient aerosol that was sampled while the measurement station was out of clouds (several thousand particles analyzed by SPLAT and ATOFMS) and to the composition of the residues of supercooled cloud droplets (SPLAT: 162 cloud droplet residues analyzed, ATOFMS: 1094). The measurements showed that mineral dust was strongly enhanced in the ice particle residues. Close to all of the SPLAT spectra from ice residues did contain signatures from mineral compounds, albeit connected with varying amounts of soluble compounds. Similarly, close to all of the ATOFMS IR spectra show a mineral or metallic component. Pure sulfate and nitrate containing particles were depleted in the ice residues. Sulfate and nitrate was found to dominate the droplet residues (∼90% of the particles). The results from the two different single particle mass spectrometers were generally in agreement. Differences in the results originate from several causes, such as the different wavelength of the desorption and ionisation lasers and different size-dependent particle detection efficiencies.

Immersion freezing of ice nucleation active protein complexes

“…In contrast, laboratory studies showed that the majority of non-biological substances found in atmospheric ice crystal residues, i.e., natural mineral dust (e.g., Twohy and Poellot, 2005;Pratt et al, 2009;Kamphus et al, 2010), are only ice active at lower temperatures (e.g., Hoose and Möhler, 2012;Murray et al, 2012). One possible explanation for the observed temperature differences might be the presence of biological material (e.g., bacteria) initiating freezing already at temperatures above −10 • C. This biological material may be internally or externally mixed with other substances in atmospheric aerosol particles (Pratt et al, 2009).…”

Atmospheric ice nucleators active ≥ −12 °C can be quantified on PM<sub>10</sub> filters

“…These results support, but do not prove until the source of IN are specifically identified, the proposition by Conen et al (2011) that larger numbers of IN per unit mass of soil dust may be found in cooler regions and where soils have larger concentrations of organic matter, compared to warmer regions or where soils have lower organic matter concentrations, such as desert soils. At the same sampling site (Jungfraujoch), Kamphus et al (2010) previously analysed single cloud ice residues by time-of-flight-massspectrometry. Mineral dust was the dominant ice residue in the mixed phase clouds they had sampled.…”

“…The horizontal resolution of these fields was 1 • by 1 • for the global and 0.2 • by 0.2 • for a nested domain covering Central Europe. Owing to the altitude mismatch between model and real world topography, particles were not released at station height but at 3000 m a.s.l., which proved to yield most realistic results in previous studies (Keller et al, 2010;Brunner et al, 2011). For each filter sample, total source sensitivities (also called footprints) (Seibert and Frank, 2004) between the surface and 100 m above model ground were calculated.…”

Evaluating the capabilities and uncertainties of droplet measurements for the fog droplet spectrometer (FM-100)

“…Several intensive cloud characterization experiments have been conducted there for many years at different times of the year (e.g. Mertes et al, 2007;Verheggen et al, 2007;Cozic et al, 2008;Targino et al, 2009;Kamphus et al, 2010;Zieger et al, 2012). The aerosol measurements performed at the JFJ are part of the Global Atmosphere Watch (GAW) program of the World Meteorological Organization since 1995 (Collaud Coen et al, 2007).…”