Atmospheric mercury sampling

Samples of atmospheric mercury were obtained by pre-concentration of mercury on columns of graphitised carbon black (Carbotrap). The columns, at ambient temperature, retained mercury vapour and alkylmercury compounds (Bloom and Fitzgerald, 1988). Methylmercury chloride, ethylmercury chloride and dimethylmercury were held on the column at temperatures as high as 29°C and air flow rates as high as 790cm3min 1. At high flow rates and high temperature,... 

When atmospheric mercury is to be measured, the mercury is preconcentrated by passing the sample through a trap containing gold-coated sand. This gold amalgamation enhances detection limits. The amalgam is next heated to desorb the mercury that is detected and measured either by AAS for concentrations within... 

Sommar j, Sprovieri E, Stevens RK, Stratton W, Tungel G and Urba A (2001) Intercomparison of methods for sampling and analysis of atmospheric mercury species. Atmos Environ 35 3007—3017. 

Atmospheric mercury is adsorbed on particulate matter and then carried down by rain (lO m per year) as explained in the corresponding section. Reported concentrations of mercury in rainwater are highly variable because most samples were collected near urban areas (Table VII) (I). As a base for calculations, a value of 0.1 fig/liter has been assumed (58). The amount of mercury in precipitation per day would be ... 

The SKC type sampler consisted of the SKC Passive Sampler for Inorganic Mercury (520 Series). The sampling method employed was OSHA ID-140 Mercury Vapor in Work Place Atmospheres. The sampling media consisted of Anasorb C300. The analytical method consisted of FGS-SOP-136 Analysis of Hg in Air via Capture on Sorbent Trap (NELAP and ISO-17025 Accredited) based on the principles of US EPA 1631 Revision E. 

Fig. 7.6. Autoclave with optical access for reflectivity measurements on fluid mercury (Hensel, 1987). One end of the sapphire window is open to the laboratory atmosphere while the other is in contact with the fluid mercury sample at high temperature and pressure. A similar system with windows at each end may be used for transmission studies.

The above nitrite (0.93 g) is dissolved in 40 ml of dry benzene and irradiated for 1 hr at 0-5° in a nitrogen atmosphere with two 200 Watt mercury lamps. The resulting suspension is concentrated and filtered to give 0.59 g of essentially pure 20a-hydroxy-18-oximinopregn-4-en-3-one as a benzene solvate mp 110-125°. Recrystallization from acetone gives an analytical sample mp 184-186° [a] 149° (CHCI3). 

D-1160 is run under vacuum (one millimeter of mercury). The results are converted to atmospheric pressure, using standard cor relations. Some newer apparatuses have built-in software that performs the conversion automatically. D-1160 is limited to a maximum EP temperature of about 1,000°F (538°C) at atmospheric pressure. Above this temperature, the sample begins to crack thermally. 

EXAMPLE 4.1 Sample exercise Calculating atmospheric pressure from the height of a column of mercury... 

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. 

The difference in mercury levels in the manometer is 19 mm. This is the pressure difference in torr between the gas sample and atmospheric pressure. The latter, as measured with a barometer, is 752 torr. Shall we add or subtract the 19 torr pressure difference Notice that the mercury level in the manometer is lower on the side exposed to the atmosphere. Thus, the atmosphere pushes on the mercury harder than does the gas sample, meaning that the pressure of the gas sample is lower than the pressure of the atmosphere. Subtract the pressure difference / gas = A P = 752 toiT - 19 toiT = 733 toiT... 

ESR spectra were recorded on a JEOL JES-RE2X spectrometer. About 250 mg of ruthenium-free titanate samples was subjected to heat treatment either in vacuum at 573 K or in a hydrogen atmosphere at 973 K. For measurements of ESR spectra, 30 Torr of O2 or N2O was introduced at room temperature and then cooled to 77 K without evacuation. The spectra were obtained in the dark and under UV irradiation with a 500 W low pressure mercury lamp. 

The second factor is the temporal variation in concentrations in different ecosystem compartments. For example, sediments and prey fish exhibit less temporal variation in mercuiy concentration than do air or water, and thus statistically valid estimates of their status can be collected with less frequent monitoring (e.g., annual sampling for prey fish vs. daily or hourly sampling for atmospheric concentrations of mercury). 

For gases and vapors, exposure concentrations are traditionally expressed in parts per million (ppm). The calculation for the ppm of a gas or vapor in an air sample is based on Avogadro s Law, which states that Equal volumes contain equal numbers of molecules under the same temperature and pressure. In other words, under standard temperature and pressure (STP), one gram-molecular weight (mole) of any gas under a pressure of one atmosphere (equivalent to the height of 760 mm mercury) and a temperature of 273 K has the same number of molecules and occupies the same volume of 22.4 liters. However, under ambient conditions, the volume of 22.4 liters has to be corrected to a larger volume based on Charles Law, which states that at constant pressure the volume of gas varies directly with the absolute temperature. Thus, at a room temperature of 25° C, one mole of a gas occupies a volume of 24.5 liters. 

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