Mercury in atmosphere

Fig. 40. Partial pressure of mercury in atmospheres as a function of 103 times the reciprocal absolute temperature along the three-phase curves for the liquids, (Hg . zCd2)yTei The value of z is shown near the bottom, -rich leg of each curve. The circles mark the pressure and temperature where =. ...

Fig. 41. The partial pressure of mercury in atmospheres plotted against 103 times the reciprocal absolute temperature for a traverse across the liquidus surface such that the atom fractions Cd and are always equal. The number near each circle give the atom fraction of mercury in the liquid phase at the pressure and temperature specified by the circle. 

Fig. 43. Partial pressure of mercury in atmospheres plotted against 103/T for various compositions. Uppermost curve is the calculated result for (Hg0 7Cd0 3)0 0. with the liqui-dus temperature indicated by the open circle. Triangles are experimental results for the same composition. Second highest curve, with the liquidus temperature again indicated by an open circle, is for the composition (Hg07Cd0 3)0 6Te04 and the squares are the experimental values. Lower four lines are the calculated results for various Hg,Te, melts along with the experimental points shown by symbols.

Burning of fuels and heating of materials which contain small amounts of the metal create man-made emissions of about lO tons/year. Thus, the background concentration in air would about double the first year and reach alarming concentrations (50 /xg/m ) in about 10 years at present emission rates if no removal processes existed. Fortunately, there is a continuous interchange between mercury in the atmosphere, soil, and water. The equilibrium between these three phases is reviewed below in relationship to biota to assess the actual accumulation of mercury in atmospheric and aqueous environments. 

Results to date indicate that levels of mercury in atmospheric fallout at Cranberry Lake are low rainfall and snowpack levels are usually less than 25 ng Hg/1 of liquid sample. The Cranberry Lake watershed contributes more mercury to the lake than it receives from the atmosphere, as stream inputs to the lake exceed... 

The plant has been shut down since 1975. At Cranberry Lake we re still getting approximately the same contribution of mercury in atmospheric fallout. So I don t know whether that may indicate that the plant had no effect except locally, or that the inactive site is still contributing mercury at some level. It would be of interest to see if that site is contaminated and giving off mercury to the air. 

A mercury barometer. This is the type of barometer first constructed by Torricelli. The pressure of the atmosphere pushes the mercury in the dish to rise into the glass tube. The height of the column of mercury is a measure of the atmospheric pressure. 

We want to find the relation between the height, h, of the column of mercury in a barometer and the atmospheric pressure, P. Suppose the cross-sectional area of the column is A. The volume of mercury in the column is the height of the cylinder times this area, V = bA. The mass, ttt, of this volume of mercury is the product of mercury s density, d, and the volume so m = dV = dhA. The mercury is pulled down by the force of gravity and the total force that its mass exerts at its base is the product of the mass and the acceleration of free fall (the acceleration due to gravity), g F = mg. Therefore, the pressure at the base of the column, the force divided by the area, is... 

The height of the mercury in the system-side column of an open-tube mercury manometer was 10. mm above that of the open side when the atmospheric pressure corresponded to 756 mm of mercury and the temperature was 15°C. What is the pressure inside the apparatus in millimeters of mercury and in pascals ... 

A student attaches a glass bulb containing neon gas to an open-tube manometer (refer to Fig. 4.5) and calculates the pressure of the gas to be 0.890 atm. (a) If the atmospheric pressure is 762 Torr, what height difference between the two sides of the mercury in the manometer did the student find ... 

When Robert Boyle conducted his experiments, he measured pressure in inches of mercury (inHg). On a day when the atmospheric pressure was 29.85 inHg, he trapped some air in the tip of a J-tube (1) and measured the difference in height of the mercury in the two arms of the tube (/ ). When b =... 

While the natural exchange of mercury between the land and atmosphere and the atmosphere and oceans is balanced, human activity has tipped this balance. There is now about three times more mercury in the atmosphere and fluxes of more than four times to and from the atmosphere. 

The average residence times for mercury in the atmosphere, terrestrial soils, oceans, and oceanic sediments are approximately 1 yr, 1000 yr, 3200 yr, and 2.5 x 10 yr, respectively. (See Bergan et al. (1999) for more details on atmospheric residence times.)... 

The air around us is a huge reservoir of gas that exerts pressure on the Earth s surface. This pressure of the atmosphere can be measured with an instmment called a barometer. Figure 5 shows a schematic view of a simple mercury barometer. A long glass tube, closed at one end, is filled with liquid mercury. The filled tube is inverted carefully into a dish that is partially filled with more mercuiy. The force of gravity pulls downward on the mercury in the tube. With no opposing force, the mercury would all ran out of the tube and mix with the mercury in the dish. 

The mercury does fall, but the flow stops at a fixed height. The column of mercury stops falling because the atmosphere exerts pressure on the mercury in the dish, pushing the column up the tube. The column is in balance when the height of the mercury column generates a downward force on the inside of the tube that exactly balances the force exerted by the atmosphere on the outside of the tube. 

At sea level, atmospheric pressure supports a mercury column approximately 760 mm in height. Changes in altitude and weather cause fluctuations in atmospheric pressure. Nevertheless, at sea level the height of the mercury column seldom varies by more than 10 mm, except under extreme conditions, such as in the eye of a hurricane, when the mercury in a barometer may fall below 740 mm. 

We must combine the reading from the manometer with the barometric pressure to find the pressure of the gas sample. The manometer displays the pressure difference in millimeters of mercury, so conversion factors are needed to express the pressure in atmospheres and bars. 

Challenges isolating the influence of changes in atmospheric emissions on mercury concentrations in the environment... 

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