R. Hitzenberger

The contribution of bacteria and fungal spores to the organic carbon content of cloud water, precipitation and aerosols

To estimate the contribution of bacterial and fungal carbon to the carbon content of atmospheric samples, the number concentrations of bacteria and fungal spores in cloud water, snow, rain and aerosol samples collected at a continental background site in the Austrian Alps were determined. Based on these number concentrations, bacterial and fungal carbon was calculated and related to the total carbon (TC) and organic carbon (OC) contents of the samples. In cloud water samples, an average of4.5 x 10 3 spores ml -1 was found, which corresponds to 1.5% of OC. The average bacterial abundance was 2.0 × 10 4 cells ml -1 corresponding to 0.01% ofOC. In snow samples, the average concentrations of bacteria and fungi were 3.1 x 10 3 cells ml -1 corresponding to 0.015% of TC and 6.2 x 10 2 spores ml -1 corresponding to 1.8% of TC, respectively. In aerosol samples, average concentration of bacteria amounted to 1.2 x 10 4 cells m -3 , which corresponds to 0.03% of OC, while fungal concentrations averaged to 7.3 x 10 2 spores m -3 3 or 0.9% ofOC. As fungal spores occur predominantly in the size range > 2.1 μm aerodynamic equivalent diameter (a.e.d.), their contribution to the coarse size fraction (2.1-10 μm) was investigated and amounted up to 9.9% ofOC.

Formic, acetic, oxalic, malonic and succinic acid concentrations and their contribution to organic carbon in cloud water

The carbon content of cloud water at a continental background site in Austria was studied during two intensive field campaigns in spring 1999 and 2000. Six carboxylic acids, total (TC) and black (BC) carbon as well as major inorganic ions were determined. Organic carbon (OC) was calculated as the difference between TC and BC. The most abundant carboxylic acids were acetic (average: 0.93 μg ml−1) and formic (0.61) followed by oxalic (0.38), succinic (0.15) and malonic (0.20) acids. Pyruvic acid was below the detection limit (<0.08) in all samples. The BC concentration was 1.15 and OC 4.81 μg ml−1 on average. Relating carboxylic acid concentrations to OC, the monocarboxylic acids alone represent 9.3% of OC. Adding the dicarboxylic acids, this average value increases to 11%. Although they are major components, no general trend could be seen between carboxylic acid and OC concentrations.

Modal character of atmospheric black carbon size distributions

Samples of atmospheric aerosols, collected with cascade impactors in the urban area of Vienna (Austria) and at a coastal site on the North Sea, were investigated for black carbon (BC) as the main component of absorbing material and for mass. The size distributions are structured. The BC distributions of these samples show a predominant mode, the accumulation aerosol, in the upper submicron size range, a less distinct finer mode attributable to fresh emissions from combustion sources, and a distinct coarse mode of unclear origin. It is important to note that some parameters of the accumulation aerosol are related statistically, indicating the evolution of the atmospheric accumulation aerosol.

CCN activation of oxalic and malonic acid test aerosols with the University of Vienna cloud condensation nuclei counter

Abstract The cloud droplet activation of monodisperse laboratory aerosols consisting of single organic and inorganic substances as well as a mixture of several substances was investigated using the University of Vienna cloud condensation nuclei counter (CCNC). The CCNC operates on the principle of a static thermal diffusion chamber. Water vapour supersaturations can be set in the range from 0.1% to 2%. Aqueous solutions of oxalic acid and malonic acid as well as solutions of inorganic compounds (NaCl and (NH4)2SO4) were nebulized in a Collison atomizer and then passed through a closed-loop differential mobility particle spectrometer to produce monodispersed particles. An internally mixed aerosol consisting of ammonium sulphate, oxalic acid and malonic acid with relative concentrations resembling those found in cloud water at a mountain station [Loflund, Kasper-Giebl, Schuster, Giebl, Hitzenberger, Reischl et al. (2002) Atmos. Environ. 36, 1553] was also investigated for cloud condensation nuclei (CCN) activation. All these particles were activated at supersaturations expected from Kohler theory. Oxalic and malonic acid particles are therefore expected to be good atmospheric CCN both as pure particles and as internally mixed particles containing other chemical compounds.

Identification of ice nucleation active sites on feldspar dust particles.

Mineral dusts originating from Earth’s crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts. Here we investigated in closer detail the reasons for its activity and the difference in the activity of the different feldspars. Conclusions are drawn from scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, and oil-immersion freezing experiments. K-feldspar showed by far the highest ice nucleation activity. Finally, we give a potential explanation of this effect, finding alkali-metal ions having different hydration shells and thus an influence on the ice nucleation activity of feldspar surfaces.

Black carbon measurements using an integrating sphere

An integrating sphere was used to determine the black carbon (BC) content of aerosol filter samples dissolved in chloroform (method originally described by Heintzenberg [1982)). The specific absorption coefficient B a (equal to absorption per mass) of the samples was also measured using the sphere as an integrating detector for transmitted light. Comparing the B a of ambient samples taken in Vienna, Austria to the BC concentrations measured on the dissolved filters, a value of approximately 6 m 2 /g was found to bea a reasonable value for the B a of the black carbon found at the site. The size dependence of B a of a nebulized suspension of soot was measured using a rotating impactor, and a reasonable agreement between measured and calculated values was found.

Scavenging Efficiency of ‘Aerosol Carbon’ and Sulfate in Supercooled Clouds at Mt. Sonnblick (3106 m a.s.l., Austria)

Cloud water and interstitial aerosol samples collected at Mt. Sonnblick (SBO) were analyzed for sulfate and ‘aerosol carbon’ to calculate in-cloud scavenging efficiencies. Scavenging efficiencies for sulfate (εSO) ranged from 0.52 to 0.99 with an average of 0.80. ‘Aerosol carbon’ was scavenged less efficiently with an average value (εAC) of 0.45 and minimum and maximum values of 0.14 and 0.81, respectively. Both εSO and εAC showed a marked, but slightly different, dependence on the liquid water content (LWC) of the cloud. At low LWC, εSO increased with rising LWC until it reached a relatively constant value of 0.83 above an LWC of ≈ 0.3 g/m3. In the case of ‘aerosol carbon’, we obtained a more gradual increase of εAC up to an LWC of ≈ 0.5 g/m3. At higher LWCs, ε_ remained relatively constant at 0.60. As the differences between εSO and εA varied across the LWC range observed at SBO, we assume that part of the ‘aerosol carbon’ was incorporated into the cloud droplets independently from sulfate. This hypothesis is supported by size classified aerosol measurements. The differences in the size distributions of sulfate and total carbon point to a partially external mixture. Thus, the different chemical nature and the differences in the size and mixing state of the aerosol particles are the most likely candidates for the differences in the scavenging behavior.

Black carbon and other species at a high‐elevation European site (Mount Sonnblick, 3106 m, Austria): Concentrations and scavenging efficiencies

During a recent measurement project, several intensive campaigns were performed on Mount Sonnblick (3106 m above sea level) in the Austrian central range of the Alps. Cloud water and interstitial aerosol samples were obtained from supercooled clouds by using a specially designed cloud water sampler [Kruisz et al., 1993]. The samples were analyzed for black carbon (BC) by an optical technique (integrating sphere [Hitzenberger et al. 1996]) using liquid samples, for major inorganic ions by ion chromatography and for total carbon (TC) by a combusion method. During the fall campaign of 1996, cloud water BC concentrations ranged from 0.45 to 3.64 μg/mL (average concentration 0.85 μg/mL). During the spring 1997 campaign, cloud water BC concentrations ranged from 0.55 to 2.95 μg/mL (average concentration 1.07 μg/mL). The dominant ion in cloud water was SO42− with concentrations from 0.36 to 86.5 μg/mL (average 6.83 μg/mL) in fall 1996 and 0.31–15.4 μg/mL (average 3.06 μg/mL) in spring 1997. In the individual samples, the BC/SO42− ratio ranged from 0.036 to 1.2 (average 0.316) in fall 1996 and 0.036 to 2.04 (average 0.79) in spring 1997. The extreme values were usually confined to short periods within one cloud event. Scavenging efficiencies e were calculated by using cloud water and interstitial aerosol concentrations from samples obtained simultaneously with the cloud water sampler for the 1997 campaign. For BC, eBC = 0.74 (±0.19) was found, while the values for SO42− and TC were eSO4 = 0.91 (±0.08) and eTC = 0.57 (±0.21), respectively. The findings of an earlier study [Kasper-Giebl et al., 2000], where eSO4 depended on the liquid water content, were confirmed here for all the three substances.

Humidity-Dependent Growth of Size-Segregated Aerosol Samples

ABSTRACT This paper presents first results obtained with a measurement system designed to measure the humidity-dependent water uptake by deposited aerosol samples. Aerosol in the size range 0.06–16 μm aerodynamic equivalent diameter is sampled with a nine stage cascade impactor. The individual impaction foils are exposed to elevated relative humidities in a chamber containing an aqueous solution of CaCl2 of specified concentration. The mass increase of the deposits is measured with a balance above the chamber. Only equilibrium values of m/m0 (i.e., wet mass/dry mass) for increasing humidities can be obtained. The two samples discussed here showed a strongly size-selective growth pattern. Deposits with accumulation range particles have larger m/m0 than those with coarse mode particles (e.g., sample 1: 2.6 vs 1.33 at 90% humidity; sample 2: 2.35 vs 1.16). Although the two samples had been obtained at the same time of the year, the growth patterns are different, which might have been caused by the meteorolog...

Comparison of particulate number concentrations in three Central European capital cities

Number size distributions of atmospheric aerosol particles in the mobility diameter range from 10 to 1000 nm were determined in Budapest, Prague and Vienna for a one-year-long period. Particle number concentrations in various size fractions, their diurnal and seasonal variations, mean size distributions and some properties of new particle formation events were derived and compared. Yearly median particle number concentrations for Budapest, Prague and Vienna were 10.6×10(3), 7.3×10(3) and 8.0×10(3) cm(-3). Differences were linked to the different pollution levels of the cities, and to diverse measurement environments and local conditions. Mean contributions of ultrafine particles (particles with a mobility diameter <100 nm) to the total number concentration were 80%, 84% and 74% for Budapest, Prague and Vienna, thus these particles represent an overwhelming share of all particles in each city. Seasonal variation of particle number concentrations was not obvious. Diurnal variations of particles with a diameter between 100 and 1000 nm (N(100-1000)) exhibited similar shape for the cities, which was related to the time-activity pattern of inhabitants and regional influences. The structure of the diurnal variation for ultrafine particles was also similar. It contained a huge morning peak in each city which was explained by emissions from vehicular traffic. The second peak was shifted from afternoon rush hours to late evenings as a result of the daily cycling in meteorological parameters. The character of the measurement site also influenced the diurnal variation. Diurnal variation of the mean ratio of ultrafine particles to N(100-1000) clearly revealed the presence and importance of new particle formation and subsequent growth in urban environments. Nucleation frequencies in Budapest and Prague were 27% and 23%, respectively on a yearly time scale. They showed a minimum in winter for both places, while the largest nucleation activity was observed in spring for Budapest, and in summer for Prague.