Development of a bioaerosol single particle detector (BIO IN) for the fast ice nucleus chamber FINCH [Discussion paper]

In this work we present the setup and first tests of our new BIO IN detector. This detector is designed to classify atmospheric ice nuclei (IN) for their biological content. Biological material is identified via its auto-fluorescence (intrinsic fluorescence) after irradiation with UV radiation. Ice nuclei are key substances for precipitation development via the Bergeron–Findeisen process. The level of scientific knowledge regarding origin and climatology (temporal and spatial distribution) of IN is very low. Some biological material is known to be active as IN even at relatively high temperatures of up to –2°C (e.g. pseudomonas syringae bacteria). These biological IN could have a strong influence on the formation of clouds and precipitation. We have designed the new BIO IN sensor to analyze the abundance of IN of biological origin. The instrument will be flown on one of the first missions of the new German research aircraft ''HALO'' (High Altitude and LOng Range)

Development of a Bioaerosol single particle detector (BIO IN) for the Fast Ice Nucleus CHamber FINCH

In this work we present the setup and first tests of our new BIO IN detector. This detector was constructed to classify atmospheric ice nuclei (IN) for their biological content. It is designed to be coupled to the Fast Ice Nucleus CHamber FINCH. If one particle acts as an ice nucleus, it will be at least partly covered with ice at the end of the development section of the FINCH chamber. The device combines an auto-fluorescence detector and a circular depolarization detector for simultaneous detection of biological material and discrimination between water droplets, ice crystals and non activated large aerosol particles. The excitation of biological material with UV light and analysis of auto-fluorescence is a common principle used for flow cytometry, fluorescence microscopy, spectroscopy and imaging. The detection of auto-fluorescence of airborne single particles demands some more experimental effort. However, expensive commercial sensors are available for special purposes, e.g. size distribution measurements. But these sensors will not fit the specifications needed for the FINCH IN counter (e.g. high sample flow of up 10 LPM). The newly developed -low cost- BIO IN sensor uses a single high-power UV LED for the electronic excitation instead of much more expensive UV lasers. Other key advantages of the new sensor are the low weight, compact size, and the little effect on the aerosol sample, which allows it to be coupled with other instruments for further analysis. The instrument will be flown on one of the first missions of the new German research aircraft "HALO" (High Altitude and LOng range)

Atmospheric ice nuclei in the Eyjafjallajökull volcanic ash plume

We have sampled atmospheric ice nuclei (IN) and aerosol in Germany and in Israel during spring 2010. IN were analyzed by the static vapor diffusion chamber FRIDGE, as well as by electron microscopy. During the Eyjafjallajökull volcanic eruption of April 2010 we have measured the highest ice nucleus number concentrations (>600 l−1) in our record of 2 yr of daily IN measurements in central Germany. Even in Israel, located about 5000 km away from Iceland, IN were as high as otherwise only during desert dust storms. The fraction of aerosol activated as ice nuclei at −18 °C and 119% rhice and the corresponding area density of ice-active sites per aerosol surface were considerably higher than what we observed during an intense outbreak of Saharan dust over Europe in May 2008. Pure volcanic ash accounts for at least 53–68% of the 239 individual ice nucleating particles that we collected in aerosol samples from the event and analyzed by electron microscopy. Volcanic ash samples that had been collected close to the eruption site were aerosolized in the laboratory and measured by FRIDGE. Our analysis confirms the relatively poor ice nucleating efficiency (at −18 °C and 119% ice-saturation) of such "fresh" volcanic ash, as it had recently been found by other workers. We find that both the fraction of the aerosol that is active as ice nuclei as well as the density of ice-active sites on the aerosol surface are three orders of magnitude larger in the samples collected from ambient air during the volcanic peaks than in the aerosolized samples from the ash collected close to the eruption site. From this we conclude that the ice-nucleating properties of volcanic ash may be altered substantially by aging and processing during long-range transport in the atmosphere, and that global volcanism deserves further attention as a potential source of atmospheric ice nuclei

Protein aggregates nucleate ice: the example of apoferritin

Biological material has gained increasing attention recently as a source of ice-nucleating particles that may account for cloud glaciation at moderate supercooling. While the ice-nucleation (IN) ability of some bacteria can be related to membrane-bound proteins with epitaxial fit to ice, little is known about the IN-active entities present in biological material in general. To elucidate the potential of proteins and viruses to contribute to the IN activity of biological material, we performed bulk freezing experiments with the newly developed drop freezing assay DRoplet Ice Nuclei Counter Zurich (DRINCZ), which allows the simultaneous cooling of 96 sample aliquots in a chilled ethanol bath. We performed a screening of common proteins, namely the iron storage protein ferritin and its iron-free counterpart apoferritin, the milk protein casein, the egg protein ovalbumin, two hydrophobins, and a yeast ice-binding protein, all of which revealed IN activity with active site densities > 0.1 mg−1 at −10 ∘C. The tobacco mosaic virus, a plant virus based on helically assembled proteins, also proved to be IN active with active site densities increasing from 100 mg−1 at −14 ∘C to 10 000 mg−1 at −20 ∘C. Among the screened proteins, the IN activity of horse spleen ferritin and apoferritin, which form cages of 24 co-assembled protein subunits, proved to be outstanding with active site densities > 10 mg−1 at −5 ∘C. Investigation of the pH dependence and heat resistance of the apoferritin sample confirmed the proteinaceous nature of its IN-active entities but excluded the correctly folded cage monomer as the IN-active species. A dilution series of apoferritin in water revealed two distinct freezing ranges, an upper one from −4 to −11 ∘C and a lower one from −11 to −21 ∘C. Dynamic light scattering measurements related the upper freezing range to ice-nucleating sites residing on aggregates and the lower freezing range to sites located on misfolded cage monomers or oligomers. The sites proved to persist during several freeze–thaw cycles performed with the same sample aliquots. Based on these results, IN activity seems to be a common feature of diverse proteins, irrespective of their function, but arising only rarely, most probably through defective folding or aggregation to structures that are IN active.This research has been supported by the Swiss National Foundation (grant nos. IZSEZ0_179149/1 and 200021_156581), the Basque government (Elkartek programmes ng 15 and ng 17), and the Spanish MINECO (grant no. MAT2013- 46006-R, programme MDM-2016-0618)

Isomerization as a Key Path to Molecular Products in the Gas-Phase Decomposition of Halons

The decomposition of halons remains controversial concerning the branching between radical and molecular products. The latter channel, where it has been found, is presumed to occur via a constrained symmetric multicenter transition state. Isomerization pathways in the gas-phase chemistry of halons have rarely been considered, despite the fact that the iso-halons, which feature a halogen−halogen bond, are widely recognized as important reactive intermediates in condensed phases. In this Letter, detailed calculations and modeling of the unimolecular decomposition of several important halons, including CF2Cl2, CF2Br2, and CHBr3, reveal that isomerization is a key pathway to molecular products. This path is important for both halons and their primary radicals as the barrier to isomerization in these compounds is typically isoenergetic with the threshold for bond fission

Characterization of soluble bromide measurements and a case study of BrO observations during ARCTAS

A focus of the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission was examination of bromine photochemistry in the spring time high latitude troposphere based on aircraft and satellite measurements of bromine oxide (BrO) and related species. The NASA DC-8 aircraft utilized a chemical ionization mass spectrometer (CIMS) to measure BrO and a mist chamber (MC) to measure soluble bromide. We have determined that the MC detection efficiency to molecular bromine (Br2), hypobromous acid (HOBr), bromine oxide (BrO), and hydrogen bromide (HBr) as soluble bromide (Br−) was 0.9±0.1, 1.06+0.30/−0.35, 0.4±0.1, and 0.95±0.1, respectively. These efficiency factors were used to estimate soluble bromide levels along the DC-8 flight track of 17 April 2008 from photochemical calculations constrained to in situ BrO measured by CIMS. During this flight, the highest levels of soluble bromide and BrO were observed and atmospheric conditions were ideal for the space-borne observation of BrO. The good agreement (R2 = 0.76; slope = 0.95; intercept = −3.4 pmol mol−1) between modeled and observed soluble bromide, when BrO was above detection limit (\u3e2 pmol mol−1) under unpolluted conditions (NOmol−1), indicates that the CIMS BrO measurements were consistent with the MC soluble bromide and that a well characterized MC can be used to derive mixing ratios of some reactive bromine compounds. Tropospheric BrO vertical column densities (BrOVCD) derived from CIMS BrO observations compare well with BrOTROPVCD from OMI on 17 April 2008

SAGE 1 and SAM 2 measurements of 1 micron aerosol extinction in the free troposphere

The SAGE 1 and SAM 2 satellite sensors were designed to measure, with global coverage, the 1 micron extinction produced by the stratospheric aerosol. In the absence of high altitude cloud, similar measurements may be made for the free tropospheric aerosol. Median extinction values in the Northern Hemisphere, for altitudes between 5 and 10 km, are found to be one-half to one order of magnitude greater than values at corresponding latitudes in the Southern Hemisphere. In addition, a seasonal increase by a factor of 1.5 yields 2 is observed in both hemispheres in local spring and summer. Following major volcanic eruptions, a long-lived enhancement of the aerosol extinction is observed for altitudes above 5 km

Relationships of Biomass-Burning Aerosols to Ice in Orographic Wave Clouds

Ice concentrations in orographic wave clouds at temperatures between −24° and −29°C were shown to be related to aerosol characteristics in nearby clear air during five research flights over the Rocky Mountains. When clouds with influence from colder temperatures were excluded from the dataset, mean ice nuclei and cloud ice number concentrations were very low, on the order of 1–5 L^(−1). In this environment, ice number concentrations were found to be significantly correlated with the number concentration of larger particles, those larger than both 0.1- and 0.5-μm diameter. A variety of complementary techniques was used to measure aerosol size distributions and chemical composition. Strong correlations were also observed between ice concentrations and the number concentrations of soot and biomass-burning aerosols. Ice nuclei concentrations directly measured in biomass-burning plumes were the highest detected during the project. Taken together, this evidence indicates a potential role for biomass-burning aerosols in ice formation, particularly in regions with relatively low concentrations of other ice nucleating aerosols