Electron tomography of nanoparticle clusters: Implications for atmospheric lifetimes and radiative forcing of soot

van Poppel, LH Friedrich, H Spinsby, J Chung, SH Seinfeld, JH Buseck, PR

GEOPHYSICAL RESEARCH LETTERS 32:24 -

Nanoparticles are ubiquitous in nature. Their large surface areas and consequent chemical reactivity typically result in their aggregation into clusters. Their chemical and physical properties depend on cluster shapes, which are commonly complex and unknown. This is the first application of electron tomography with a transmission electron microscope to quantitatively determine the three-dimensional (3D) shapes, volumes, and surface areas of nanoparticle clusters. We use soot (black carbon, BC) nanoparticles as an example because it is a major contributor to environmental degradation and global climate change. To the extent that our samples are representative, we find that quantitative measurements of soot surface areas and volumes derived from electron tomograms differ from geometrically derived values by, respectively, almost one and two orders of magnitude. Global sensitivity studies suggest that the global burden and direct radiative forcing of fractal BC are only about 60% of the value if it is assumed that BC has a spherical shape.

sarubh:unrelated | /unrelated | 285

Fish use and size of eelgrass meadows in southeastern Alaska: A baseline for long-term assessment of biotic change

Johnson, SW Thedinga, JF

NORTHWEST SCIENCE 79:2-3 141-155

Eelgrass meadows at six sites in southeastern Alaska were sampled for fish assemblages and mapped to establish a baseline of information for long-term assessment of biotic change. All sites were sampled in spring 2001, 2002, and 2003: four of the sites were also sampled in winter 2003. A total of 44 seine hauls from all sampling periods yielded 58,902 fish comprising 45 species. Fish abundance in spring differed significantly among sites but not among years. The most abundant commercially important or forage fish species captured were chum salmon, Pacific herring. pink salmon, coho salmon, and Pacific sand lance: mean size of each of these species was <= 100 mm FL. For those sites sampled seasonally in 2003, fish were significantly more abundant in spring than in winter. At each site, three different species accounted for most (>= 69%) of the total catch. Size of eelgrass meadows varied annually; maximum percent change in area ranged from -13% to +27%. Eelgrass density ranged from 336 shoots/m(2) to 1,544 shoots/m(2), and dry biomass ranged from 36 g/m(2) to 71 g/m(2). Periodic re-sampling of the eelgrass sites established in this study will allow resource managers to track long-term and large-scale changes in fish communities and habitat that may result from shoreline development or global climate change.

sarubh:unrelated | /unrelated | 291

Seductive simulations? Uncertainty distribution around climate models

Lahsen, M

SOCIAL STUDIES OF SCIENCE 35:6 895-922

This paper discusses the distribution of certainty around General Circulation Models (GCMs) - computer models used to project possible global climatic changes due to human emissions of greenhouse gases. It examines the trope of distance underpinning Donald MacKenzie’s concept of ‘certainty trough’, and calls for a more multi-dimensional and dynamic conceptualization of how uncertainty is distributed around technology. The certainty trough describes the level of certainty attached to particular technoscientific constructions as distance increases from the site of knowledge production, and proposes that producers of a given technology and its products are the best judges of their accuracy. Processes and dynamics associated with GCM modeling challenge the simplicity of the certainty trough diagram, mainly because of difficulties with distinguishing between knowledge producers and users, and because GCMs involve multiple sites of production. This case study also challenges the assumption that knowledge producers always are the best judges of the accuracy of their models. Drawing on participant observation and interviews with climate modelers and the atmospheric scientists with whom they interact, the study discusses how modelers, and to some extent knowledge producers in general, are sometimes less able than some users to identify shortcomings of their models.

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