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Abstract. This paper discusses the influence of primary biological aerosols (PBA) on atmospheric chemistry and vice versa through microbiological and chemical properties and processes. Several studies have shown that PBA represent a significant fraction of air particulate matter and hence affect the microstructure and water uptake of aerosol particles. Moreover, airborne micro-organisms, namely fungal spores and bacteria, can transform chemical constituents of the atmosphere by metabolic activity. Recent studies have emphasized the viability of bacteria and metabolic degradation of organic substances in cloud water. On the other hand, the viability and metabolic activity of airborne micro-organisms depend strongly on physical and chemical atmospheric parameters such as temperature, pressure, radiation, pH value and nutrient concentrations. In spite of recent advances, however, our knowledge of the microbiological and chemical interactions of PBA in the atmosphere is rather limited. Further targeted investigations combining laboratory experiments, field measurements, and modelling studies will be required to characterize the chemical feedbacks, microbiological activities at the air/snow/water interface supplied to the atmosphere.

The variability of optical properties of combustion particles generated from a propane diffusion flame under varying fuel-toair (C/O) ratios was studied with a three-wavelength nephelometer, a particle soot absorption photometer, and an integrating sphere photometer. Information on particle size distribution, morphology, and elemental carbon to total carbon (EC/TC) ratios were obtained from scanning mobility particle sizer measurements, transmission electron microscopy analyses, and thermal-optical analyses. Particles generated under a low C/ O ratio (0.22) showed high elemental carbon fraction (EC/TC D 0.77) and low brown carbon to equivalent black carbon (BrC/ EBC) ratio (0.01), and were aggregates composed of small primary particles. Rayleigh-Debye-Gans theory reproduced experimental single-scattering albedo, v, absorption, and scattering A ngstr€ om exponents within 56, 3, and 18%, respectively. In contrast, particles produced under a high C/O ratio (0.60) showed low elemental carbon fraction (EC/TC D 0.09) and high BrC/EBC ratio >100, and were smaller and spherical in shape. Their optical properties were better modeled with Mie theory. By minimizing the difference between calculated and measured v and A ngstr€ om exponents, refractive indices of OC at three visible wavelengths were deduced. Contrary to the widely accepted assumption that refractive index of BC is wavelength independent, BC-rich particles exhibited absorption A ngstr€ om exponent >1.0 which implies some degree of wavelength dependence.

Abstract. This paper discusses the influence of bioaerosols on atmospheric chemistry and vice versa through microbiological and chemical properties and processes. Several studies have shown that biological matter represents a significant fraction of air particulate matter and hence affects the microstructure and water uptake of aerosol particles. Moreover, airborne micro-organisms can transform chemical constituents of the atmosphere by metabolic activity. Recent studies have emphasized the viability of bacteria and metabolic degradation of organic substances in cloud water. On the other hand, the viability and metabolic activity of airborne micro-organisms depend strongly on physical and chemical atmospheric parameters such as temperature, pressure, radiation, pH value and nutrient concentrations. In spite of recent advances, however, our knowledge of the microbiological and chemical interactions of primary biological particles in the atmosphere is rather limited. Further targeted investigations combining laboratory experiments, field measurements, and modelling studies will be required to characterize the chemical feedbacks, microbiological activities at the air/snow/water interface supplied to the atmosphere.

In order to obtain reliable data of the dark conductivity for Si2Te3 single crystals it is necessary to use samples with ohmic contacts and low condctivity surface layer. It is shown that these conditions can be met by evaporation of gold contacts after vacuum cleaving and a subsequent heat treatment, which produces a SiO2 surface layer. The results of de and ac conductivity measurements indicate a thermal activation of the carrier mobility parallel to the c‐axis.