Sabine Matthias-Maser

composition and diurnal variability of the natural Amazonian aerosol

As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment (CLAIRE) 2001 campaign, separate day and nighttime aerosol samples were collected in July 2001 at a ground-based site in Amazonia, Brazil, in order to examine the composition and temporal variability of the natural “background” aerosol. A combination of analytical techniques was used to characterize the elemental and ionic composition of the aerosol. Major particle types larger than ∼0.5 μm were identified by electron and light microscopy. Both the coarse and fine aerosol were found to consist primarily of organic matter (∼70 and 80% by mass, respectively), with the coarse fraction containing small amounts of soil dust and sea-salt particles and the fine fraction containing some non-sea-salt sulfate. Coarse particulate mass concentrations (CPM ≈ PM_(10) − PM_2) were found to be highest at night (average = 3.9 ± 1.4 μg m^(−3), mean night-to-day ratio = 1.9 ± 0.4), while fine particulate mass concentrations (FPM ≈ PM_2) increased during the daytime (average = 2.6 ± 0.8 μg m^(−3), mean night-to-day ratio = 0.7 ± 0.1). The nocturnal increase in CPM coincided with an increase in primary biological particles in this size range (predominantly yeasts and other fungal spores), resulting from the trapping of surface-derived forest aerosol under a shallow nocturnal boundary layer and a lake-land breeze effect at the site, although active nocturnal sporulation may have also contributed. Associated with this, we observed elevated nighttime concentrations of biogenic elements and ions (P, S, K, Cu, Zn, NH_4^+) in the CPM fraction. For the FPM fraction a persistently higher daytime concentration of organic carbon was found, which indicates that photochemical production of secondary organic aerosol from biogenic volatile organic compounds may have made a significant contribution to the fine aerosol. Dust and sea-salt-associated elements/ions in the CPM fraction, and non-sea-salt sulfate in the FPM fraction, showed higher daytime concentrations, most likely due to enhanced convective downward mixing of long-range transported aerosol.

The ice nucleating ability of pollen: Part I: Laboratory studies in deposition and condensation freezing modes

Abstract Laboratory experiments are described where the water uptake by a variety of pollen was studied quantitatively, followed by the investigation of the ice nucleating ability of four kinds of pollen in the deposition and the condensation freezing modes. The diameters of the pollen selected for the freezing experiments were between 25 and 70 μm. The freezing experiments in the deposition mode including also pollen resuspended from decayed leaves, and crushed pollen grains were carried out at different temperatures down to −33 °C combined with various supersaturations with respect to ice up to 35%. The condensation freezing experiments were carried out at temperatures down to −18 °C at supersaturation with respect to water above 100%. The results showed that all investigated pollen were able to take up significant amounts of water from a humid environment into their interior by capillary effect. The results of the freezing experiments in the deposition mode showed that none of the investigated pollen acted as deposition ice nuclei within the investigated temperature and ice supersaturation ranges. Pollen was found to act as condensation ice nuclei at relatively warm temperatures. The initiation temperature for freezing activation of all pollen was around −8 °C, while a mean condensation freezing efficiency of 50% was reached at different temperatures between −12 and −18 °C.

The size distribution of primary biological aerosol particles with radii > 0.2 μm in an urban/rural influenced region

Abstract Primary biological aerosol particles including pollen, spores, plant debris, epithelial cells, bacteria, algae, protozoa and viruses, are an ubiquitous component of the atmospheric aerosol, they are most probably present in all size ranges. Besides their effects on air hygiene and health, biological particles play an important role in cloud physics, for example some bacteria are able to accumulate water and act as ice nuclei. To sample aerosols a two-stage-slit-impactor and a wing-impactor are used to collect particles for a following single particle analysis. The coarse particles are sampled on dyed glycerine jelly. The biological particles become stained and can be distinguished in contrast to the non-dyed particles using a light microscope. The small particles are examined in a scanning-electron-microscope equipped with an energy dispersive X-ray spectrometer after sampling on graphitic foils. Three criteria were used to characterize the particles: the morphology, the elemental composition and the behaviour during the microanalysis. With this method the size distributions of the primary biological aerosol particles were determined in an urban/rural influenced region. Considering all measurements we calculated a mean number concentration of 1.9 cm −3 of biological aerosol particles ≈30% of the total aerosol particles. The mean volume concentration was about 15% of the total volume. A model size distribution for primary biological aerosol particles was obtained by performing a non-linear fitting procedure.

The ice nucleating ability of pollen:: Part II. Laboratory studies in immersion and contact freezing modes

Abstract Laboratory tests were conducted of the ice nucleating ability of four kinds of pollen in the immersion and the contact freezing modes. The diameters of the selected pollen were between 25 and 70 μm. The experiments were carried out at the Mainz vertical wind tunnel with freely suspended supercooled droplets at temperatures down to −28 °C. The immersion freezing experiments were conducted with drops of radii between 250 and 375 μm formed from distilled water with a defined amount of pollen added. The drops were freely floated in the wind tunnel while being supercooled. For the contact freezing experiments, a short burst of pollen was allowed to collide with freely suspended, supercooled pure water drops of 360-μm radius. The results showed that particle-free water drops in particle-free air in the wind tunnel did not freeze at temperatures above −28 °C while water drops containing pollen froze at temperatures as high as −9 °C, and water drops colliding with pollen froze at temperatures −5 °C and lower. Combined with earlier results about the ice nucleating ability of some bacteria, marine plankton, and leaf litters, the present results confirm the importance of biological aerosol particles as potential ice nuclei at relatively warm temperatures.

Examination of atmospheric bioaerosol particles with radii > 0.2 μm

Abstract Besides their effects on air hygiene and health, bioaerosol particles play an important role in cloud physics, for example, some bacteria are able to accumulate water and act as ice nuclei. For sampling aerosol particle impactors were used. The larger particles were sampled size fractionated with a free wing impactor while for the smaller ones an isokinetic two-stage impactor was constructed. The bioaerosol particles of the coarse fraction were stained with a protein dye and could be distinguished from the non-dyed particles using an optical light microscope. The small particles were examined in a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX). Three criteria were used to characterize the particles: morphology, elemental composition and behaviour during EDX. Literature and the results of our own experiments with test aerosols showed that biological particles have a special morphology together with a special elemental composition and also some of them change their form during EDX. Based on these criteria a scheme was developed dividing the atmospheric aerosol into six groups, each of them representing biological or non-biological particles.

Omnipresence of biological material in the atmosphere

Environmental context. Atmospheric biological particles have been largely overlooked in the past. While some microorganisms have been studied, the majority of other biological particles have not. The presence of these particles might force us to view the atmospheric aerosol differently. Abstract. Measurements of biological particles in the atmosphere during the last decade indicate that the presence of these particles seems to have been underestimated by atmospheric scientists. On the average these primary aerosol particles might be present as much as 25% of the total mass (or number for particles with radius greater than 0.2 µm) concentration of the atmospheric aerosol. Such a large fraction certainly plays a major role in all processes affected by atmospheric aerosols, such as cloud and precipitation formation, climate forcing, visibility, turbidity, and so on. This disregard of the biological particles requires a new attitude in our opinion.

The size distribution of primary biological aerosol particles in cloud water on the mountain Kleiner Feldberg/Taunus (FRG)

During the field campaign, FELDEX 95 cloud water samples were collected and the insoluble particles were analysed by single particle analysis in order to determine the content of primary biological aerosol particles (PBAP). It is found that 25% of the total insoluble particles are biological ones. During cloud events with increasing wind velocity, the concentration of biological particles also increases. Anthropogenic influence leads to a higher amount of both total and biological particles. Within the size distribution, the percentage of biological particles decreases with increasing radius.

The size distribution of primary biological aerosol particles in the multiphase atmosphere

Primary biological aerosol particles are a ubiquitouscomponent of the atmospheric aerosol and have greatimportance within the whole atmosphere. Besides theireffect on air hygiene (i.e. causing allergic diseases), theycontribute to cloud and rain development. They amountto almost 25% of the total number of aerosolparticles both in dry air and in cloudwater. They showno seasonal variation in concentration but incomposition.

A method to identify biological aerosol particles with radius > 0.3μmfor the determination of their size distribution

Abstract The relevance of biological aerosol will be demonstrated. A method to determine the sizedistribution of the biological aerosols is shown, which gives the opportunity to determine a lower limit of the biological particles. For evaluation a light microscope and a scanning electron microscope equipped with an energy dispersive x-ray spectrometer are used.

The size distribution of primary biological aerosol particles in rain-water

Publisher Summary This chapter demonstrates the relevance of biological aerosol particles as active participants in cloud forming processes. It uses an existing method for the determination of atmospheric biological aerosol particles to investigate rain-water samples and this size distribution in rainwater. Primary biological aerosol particles (PBAP) describe airborne solid particles that are derived from living organisms, including microorganisms and fragments of all varieties of living things. This definition includes a wide spectrum of biological particles spread over a large size range. The larger particle range includes bacteria, algae, spores of lichen, mosses, ferns, and fungi, pollen, plant debris like leaf litter, parts of insects, human, and animal epithelial cells. They are a ubiquitous component of the atmospheric aerosol and come to about 24% of the concentration of the total atmospheric particles. Besides their effects on air hygiene, they play an important role in cloud physics. Schnell and Vali suggested that a portion of atmospheric freezing nuclei was of biogenic origin. The sources of these nuclei include decaying vegetation, marine plankton, and bacteria. The peculiarity of the bacteria is that they have a freezing capability even at temperatures about -4° C while most mineral particles need temperatures below -10° C.