Atmospheric mercury speciation in Yellowstone National Park.

Atmospheric concentrations of elemental mercury (Hg(0)), reactive gaseous Hg (RGM), and particulate Hg (pHg) concentrations were measured in Yellowstone National Park (YNP), U.S.A. using high resolution, real time atmospheric mercury analyzers (Tekran 2537A, 1130, and 1135). A survey of Hg(0) concentrations at various locations within YNP showed that concentrations generally reflect global background concentrations of 1.5-2.0 ng m(-3), but a few specific locations associated with concentrated geothermal activity showed distinctly elevated Hg(0) concentrations (about 9.0 ng m(-3)). At the site of intensive study located centrally in YNP (Canyon Village), Hg(0) concentrations did not exceed 2.5 ng m(-3); concentrations of RGM were generally below detection limits of 0.88 pg m(-3) and never exceeded 5 pg m(-3). Concentrations of pHg ranged from below detection limits to close to 30 pg m(-3). RGM and pHg concentrations were not correlated with any criteria gases (SO(2), NO(x), O(3)); however pHg was weakly correlated with the concentration of atmospheric particles. We investigated three likely sources of Hg at the intensive monitoring site: numerous geothermal features scattered throughout YNP, re-suspended soils, and wildfires near or in YNP. We examined relationships between the chemical properties of aerosols (as measured using real time, single particle mass spectrometry; aerosol time-of-flight mass spectrometer; ATOFMS) and concentrations of atmospheric pHg. Based on the presence of particles with distinct chemical signatures of the wildfires, and the absence of signatures associated with the other sources, we concluded that wildfires in the park were the main source of aerosols and associated pHg to our sampling site.

Recovery of a temporally based visual discrimination after visual cortex lesion in the rat.

In Expt. 1, rats were conditioned to emit a shock avoidance response when the pulse rate of a light was increased. Then, after bilateral visual cortex lesions, the rats were given 10, 20, or 40 days recovery before relearning the discrimination. While all rats were able to relearn the discrimination response, lesion rats had a performance deficit after all recovery periods. Expt. 2 compared the effects of postoperative visual pulse rate training to those of auditory pulse rate training on relearning of the photic pulse-rate discrimination 10 days after visual decortication. Recovery of discrimination responding was better after auditory pulse rate training than after visual training. These data suggest that visual cortex lesions in the rat disrupt perceptual or associational functions involving the temporal features of a visual stimulus. In addition, generalization of relational properties during cross-modal training through multimodal CNS structures appears to enhance recovery of behavior after brain insult.