BS 15853:2010 pdf download – Ambient air quality — Standard method for the determination of mercury deposition
6.9 Bromine monochloride (BrCl) solution, 0,5 % V/V for cleaning purposes, prepared of Bromine monochloride (BrCl) solution (6.8) by dilution with ultrapure water (6.3).
6.10 Hydroxylammonium hydrochloride solution. Dissolve 12,0 g NH 2 OH·HCl in 100 ml water (6.3). This chemical reagent sometimes contains high mercury concentrations. Adding 0,1 g Chelex 100 ion exchange material can lower the mercury content. Blanks shall be checked carefully. NOTE Instead of hydroxylammonium hydrochloride solution ascorbic acid can be used. Ascorbic acid solution can be prepared weekly by dissolving 10 g of L-ascorbic acid in 100 ml water (6.3).
7.1 Sampling equipment – General requirements Use collectors with a defined horizontal opening, either a funnel/bottle combination (see A.1 and A.3) or a wide-mouthed jar (see A.2). The collectors can be bulk samplers, which collect at all times, or wet-only samplers which collect only during wet precipitation events. If a funnel/bottle collector is used, the funnel shall have a cylindrical vertical section of sufficient height to avoid sampling losses resulting from splashing. If a jar is used, it shall have a sufficient depth to avoid such sampling losses. Collector dimensions shall be selected with respect to the expected precipitation collected in the sampling period used.
Typical sampling periods vary between one week and one month.
The funnel area shall be large enough to provide sufficient sample for chemical analysis at a minimum precipitation depth of 1 mm per week.
It is recommended that short sampling periods (weekly) and/or two or three samplers in parallel are used. The sampling efficiency of funnel/bottle collectors can be checked by comparing the collected precipitation with the precipitation determined using a standard meteorological rain gauge. The difference in precipitation between the standard rain gauge and the heavy metal sample collector shall not be greater than 20 % for precipitation depths between 1 mm to 2,5 mm, and not greater than 10 % for precipitation depths larger than 2,5 mm of precipitation .
Checking sampling efficiency is especially important if a wet-only collector is used. Mercury deposition is collected in special precipitation samplers, which are used only for mercury deposition determinations. All parts of the precipitation collector that are in contact with the sample shall consist of materials that do not alter the mercury content of the sample (e.g. glass, fluorocarbon polymers). Also, all parts of the sampling collectors shall be easy to clean.
In order for the sample not to be contaminated during heavy rain, the rim of the funnel shall be positioned 1,5 m to 2,0 m above the ground level. NOTE Sample contamination can be caused by insects, bird droppings or other material in the sampling vessels, especially when using extended sampling periods. This is a major drawback to bulk sampling.
For extended sampling periods − especially if HCl is used to preserve the sample during exposure − it is necessary to prevent the diffusion of Hg 0 into the precipitation sample collected, since it could contribute to the mercury content of the sample via oxidation to water-soluble forms. For funnel/bottle collectors this can be done easily by using a capillary tube between the funnel and the bottle. It is also necessary to shield the sample bottles from light to avoid photo-induced reduction of the mercury in the precipitation sample.
If a funnel/bottle collector with capillary tube is used, add HCl (6.1 or 6.5) to the sampling bottle before exposure in order to stabilize the sample (see 7.3). Do not add acid, if an open jar is used for sampling. Samplers shall be suitable for all seasons and all climatic conditions. Thus, especially for wet-only collectors, a heating device should be included to melt snow and to prevent the formation of ice in the funnel and bottle during winter. Otherwise, for bulk collectors, an extra large and deep cylindrical jar should be used for snow sampling. It can be useful to cool the samples in locations where high temperatures are expected during summer.