Ice-nucleating ability of aerosol particles and possible sources at three coastal marine sites

Despite the importance of ice-nucleating particles (INPs) for climate and precipitation, our understanding of these particles is far from complete. Here, we investigated INPs at three coastal marine sites in Canada, two at mid-latitude (Amphitrite Point and Labrador Sea) and one in the Arctic (Lancaster Sound). For Amphitrite Point, 23 sets of samples were analyzed, and for Labrador Sea and Lancaster Sound, one set of samples was analyzed for each location. At all three sites, the ice-nucleating ability on a per number basis (expressed as the fraction of aerosol particles acting as an INP) was strongly dependent on the particle size. For example, at diameters of around 0.2 µm, approximately 1 in 106 particles acted as an INP at −25 ∘C, while at diameters of around 8 µm, approximately 1 in 10 particles acted as an INP at −25 ∘C. The ice-nucleating ability on a per surface-area basis (expressed as the surface active site density, ns) was also dependent on the particle size, with larger particles being more efficient at nucleating ice. The ns values of supermicron particles at Amphitrite Point and Labrador Sea were larger than previously measured ns values of sea spray aerosols, suggesting that sea spray aerosols were not a major contributor to the supermicron INP population at these two sites. Consistent with this observation, a global model of INP concentrations under-predicted the INP concentrations when assuming only marine organics as INPs. On the other hand, assuming only K-feldspar as INPs, the same model was able to reproduce the measurements at a freezing temperature of −25 ∘C, but under-predicted INP concentrations at −15 ∘C, suggesting that the model is missing a source of INPs active at a freezing temperature of −15 ∘C.

Ice-nucleating efficiency of aerosol particles and possible sources at three coastal marine sites

Despite the importance of ice-nucleating particles (INPs) for climate and precipitation, our understanding of these particles is far from complete. Here, we investigated INPs at three coastal marine sites in Canada, two at mid-latitude (Amphitrite Point and Labrador Sea), and one in the Arctic (Lancaster Sound). At all three sites, the ice-nucleating efficiency on a per number basis (expressed as the fraction of aerosol particles acting as an INP) was strongly dependent on the size. For example, at diameters of around 0.2 µm, approximately 1 in 106 particles acted as an INP at −25 ºC, while at diameters of around 8 µm, approximately 1 in 10 particles acted as an INP at −25 ºC. The ice-nucleating efficiency on a per surface area basis (expressed as the surface active site density, ns) was also dependent on the size, with larger particles being more efficient at nucleating ice. The ns values of supermicron particles at Amphitrite Point and Labrador Sea were larger than previously measured ns values of sea spray aerosol, suggesting that sea spray aerosol was not a major contributor to the supermicron INP population at these two sites. Consistent with this observation, a global model of INP concentrations under-predicted the INP concentrations when assuming only marine organics as INPs. On the other hand, assuming only K-feldspar as INPs, the same model was able to reproduce the measurements at a freezing temperature of −25 ºC, but under-predicted INP concentrations at −15 ºC, suggesting that the model is missing a source of INPs active at a freezing temperature of −15 ºC.

Catalytic Activity and Surface Characterization Study of Pd Supported on Nanocrystalline and Polycrystalline CeO2

ABSTRACTThe catalytic activity of polycrystalline and nanocrystalline CeO2-supported Pd (Pd/pCeO2 and Pd/nCeO2) has been determined as a function of temperature and Pd loading. While the untreated nCeO2 support gives 50% methane conversion at 420°C, the untreated pCeO2 support exhibits little activity under the conditions examined due to its low surface area. A Pd loading of 5 wt% increases the activity of pCeO2 to 50% conversion at 260°C, while a 40 wt% Pd loading on nCeO2 exhibits a relatively smaller activity increase, yielding 50% conversion at 240°C. On a mass basis the 40 wt% Pd/nCeO2 catalyst is the most active tested in this study, but it is less active than the 5 wt% Pd/pCeO2 catalyst on a surface-area basis. Furthermore, the activity of the 40 wt% Pd/nCeO2 catalyst does not decrease during 100 hrs of exposure to CH4 and O2 at 250°C.X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) have been used to characterize the surfaces of both bare supports and Pd-containing catalysts before and after exposure to reactor conditions. The XPS results reveal that the Pd surface concentration is more than an order of magnitude higher for 5 wt% Pd/pCeO2 than for 5 wt% Pd/nCeO2 due to the larger surface area of nCeO2 and that the 40 wt% Pd/nCeO2 catalyst has a lower Pd loading on a surface-area basis than the 5 wt% Pd/pCeO2 catalyst. Most of the supported Pd is in the form of PdO, but higher PdO2/PdO ratios are observed for both CeO2 supports compared to Pd supported on ZrO2 or CO3O4. Furthermore, a significant amount of metallic Pd forms on Pd/nCeO2 but not on Pd/pCeO2 during reaction. The nanocrystalline and polycrystalline CeO2 behave differently chemically which is consistent with the fact that the nanocrystalline catalysts are less active on a surface-area basis. Accumulation of H20 on the Pd/pCeO2 surface during reaction is significant but not on the Pd/nCeO2 surface. This suggests that the rate limiting step may be H2O desorption on Pd/pCeO2 while for Pd on nCeO2 adsorption of methane appears to be the slow step. The ISS data indicate that the outermost atomic layer of Pd/nCeO2 consists mostly of O and C, which is not the case for Pd/pCeO2. Site blockage by these species may also contribute to the lower activity on a surface-area basis of Pd/nCeO2 compared to Pd/pCeO2.

The disposition of benzo(a)pyrene in the periphyton communities of two South Carolina streams: uptake and biotransformation

The effect of periphyton community composition and colonization time on the uptake and biotransformation of benzo(a)pyrene (BaP) was determined in laboratory studies. Naturally colonized glass microscope slides were collected after 3 and 6 weeks from Castor Creek, which has a predominantly desmid flora, and after 3 and 5 weeks from diatom-dominated Upper Three Runs Creek. When expressed on a slide surface-area basis, the Castor Creek periphyton showed significantly greater BaP uptake rates at both colonization periods. Within streams, uptake rates increased significantly with colonization time. Autoradiographic analysis suggests that BaP was accumulated by surface sorption, especially to gelatinous sheath material. Active biotransformation as measured by the percentage extractable non-BaP 14C was not detected in either community.

Ectomycorrhizal fungi of Salix rotundifolia III. Resynthesized mycorrhizal complexes and their surface phosphatase activities

Pure culture isolates were obtained from fungi fruiting in the vicinity of dwarf willows at Barrow and Cape Simpson, Alaska. Four of these isolates and one isolate from Maryland were tested for their ability to form ectomycorrhizae with cuttings of Salix rotundifolia under controlled environmental conditions. Isolates of Entoloma sericeum, Hebelomapusillum, and Cenococcum geophilum from Barrow and Cape Simpson, Alaska all formed typical ectomycorrhizae with S. rotundifolia, while an isolate of C. geophilum from a temperate ecosystem (Maryland) did not.All of the ectomycorrhizae synthesized with S. rotundifolia, plus uncolonized roots, demonstrated an ability to hydrolyze p-nitrophenyl phosphate at a pH of 4.7. The acid phosphatase activity of E. sericeum ectomycorrhizae was from 10 to 40 times as great as that demonstrated by other mycorrhizal and nonmycorrhizal roots on a surface area basis.

Quantitative assessment of the bacterial rhizosphere flora of Pinus contorta var. latifolia

The bacterial flora associated with root systems of young and mature lodgepole pine was investigated by sampling forest-grown trees. Counts were performed and expressed on a surface-area basis to give a more realistic comparison of organism density or activity within the control soil, rhizosphere soil, and rhizoplane. On this basis, densities increased by an order of 104- to 106-fold from control soil to rhizoplane, with the degree of stimulation being inversely related to root radius.

The Surface-Area/Body-Weight Relationship in Mice

Since Sarrus and Remeaux (see Kleiber 1961, p. 180) first proposed a "surface law", the measured or calculated surface area of animals has been used by many workers as a basis for comparison between individuals and between species in studies of metabolic rate. The history of the surface law has been discussed by Kayser (1951) and by Kleiber (1961). The DuBois standards for determining the surface area of humans have served for many years as a valuable basis for comparison between individuals in physiological and clinical studies of metabolic rate. However, standards similar to the DuBois standards for humans do not exist for other species. The trend in recent work on metabolic rate of animals appears to be to make comparisons on a body-weight basis rather than on a surface-area basis. The work reported in this paper was designed to investigate the usefulness of surface area as a basis for comparison in some studies on metabolic rate of mice.

Reactions between boron and clays

Sorption of boron by Kent sand kaolinite, WilIalooka illite, and Marchagee montmorillonite in 0.01M CaCl2 is consistent with a mechanism described by the Langmuir equation, except that deviations occur at solution concentrations greater than about 10 �g B/ml. The quantity of boron adsorbed increases markedly with pH, and is rapid, reversible, and unaffected by the concentration of calcium chloride present. Complete desorption of surface boron, without significant solution of lattice boron, is achieved with 0.01M mannitol solution. Comparing the three clays at pH 7.5 on a surface area basis, the illite is most reactive (1.18 �g B/m2), followed by the kaolinite (0.28 �g B/m2) and the montmorillonite (0.02 �g B/m2). For illite, which is the most reactive of the three minerals, the magnitude of the above values emphasizes the small proportion (less than 1.4%) of the total surface area occupied by boron. Consideration of the reaction between boron and clays suggests that either boric acid molecules or borate ions could be the adsorbed species. Increasing sorption with pH could be explained either by the increasing proportion of borate ions to boric acid with pH or by a greater number of sites on the clay surface at higher pH values.

FUNCTION OF ADRENAL CORTEX IN PREMATURE INFANTS

Urinary formaldehydogenic steroid excretions were measured in eight premature infants without recognized disease for varying periods up to 2 months of age. A balance study for Na, K and N was carried out in one infant. Urinary formaldehydogenic steroid excretion did not change measurably during the first 10 days of life, and was not significantly different from adult normal values when compared on a surface area basis. Calculations from the data of other investigators indicate that infant values are from 1 to 5 times those of adults when compared by surface area. Urinary formaldehydogenic steroid excretions rose significantly with age when the entire period of study for all infants was included. This rise occurred during the period of fetal cortical involution and is evidence that the fetal zone is not an important source of formaldehydogenic steroids. The nitrogen and electrolyte balance study revealed a loss of K in the first 2 days of life which was disproportionately greater than the loss of N during the postnatal fasting period. The formaldehydogenic steroid excretion did not change measurably at this time, so that the study does not support the concept of changed adrenal function as a cause for this K/N disproportion. The electrolyte-regulating hormones can, however, vary independently of other adrenal functions. Acute inanition in the neonatal period of fasting is suggested as a possible cause for the disproportion.