Elemental mercury is a liquid metal and at room temperature readily vaporizes due to its low vapor pressure. In order to understand mercury vapor, an understanding of some physical properties is required:
• Vapor pressure (mm Hg) is 0.0018 @ 77° F
• Vapor density is 7.0 (Air = 1)
• Evaporation Rate is 4 (n-Butyl acetate = 1)
• Mercury evaporates at a rate of 7.0 µg/cm2/hour at 68° F (Adren & Nriagu, 1979)
• There are about 1,501,430,636,558,496,585,414 atoms in 0.5 grams of mercury (1021)
The vaporization rate of mercury is proportional to ambient and surface temperature – the higher the temperature, the more mercury vaporizes.
Effects of Temperature on Saturated Mercury Vapor Concentrations
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Effects of Temperature on Saturated Mercury Vapor Concentrations
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T-Fahrenheit
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Concentration (mg/m3)
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Pressure (mmHg)
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Concentration (mg/m3)
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32
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2.5826
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0.000185
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2.18
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41
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3.8915
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0.000306
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3.53
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50
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5.8638
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0.00049
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5.56
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59
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8.8357
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0.000776
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8.66
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68
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13.3138
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0.0012
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13.20
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The resonance absorption of mercury vapor, in the form of mercury atoms is 254 nm on the electromagnetic spectrum, which is above the visible range for humans.
The photograph and video above demonstrates that mercury emits vapor at room temperature. In order to see mercury vapor with the naked eye, a short-wave ultraviolet light is used to project onto a fluorescent background. On a fluorescent background, a shadow is indicated as the mercury atoms within the vapor absorb the light energy. The amount of light absorbed is proportional to the concentration of the mercury as demonstrated in the video.
Since mercury vapor is odorless, tasteless and colorless, it is necessary to use mercury vapor analyzers (MVA’s) to detect the presence of mercury in air.
