Ammonium deposition

In areas with large snowpacks (e.g., much of the Northeast and all of the mountainous West), ions have been shown to drain from the pack in the early stages of snowmelt. This process leads to concentrations that are much higher than the average concentration of the snowpack itself (82). D ifferential elution of acid anions (like N03") during the initial stages of snowmelt has been shown to be responsible for the elevated N03" concentrations observed in parts of Scandinavia (81), Canada (82), the Adirondack Mountains (181), the Midwest (182), and the Sierra Nevada Mountains (180). Ammonium deposited to the snowpack (either wet or dry deposition) can subsequently... 

A combination of measurements and simulations have indicated that cloudwater sulfate, acidity, nitrate, and ammonium deposition exceeds wet deposition via precipitation for some NE U.S. sites located above 400 m. While the current large uncertainties that are associated with cloudwater deposition models make firm estimates impossible, the available data indicate that cloudwater deposition is a substantial contributor to wet deposition inputs to high elevation sites in the eastern United States. Similar conclusions have been reached by European studies. 

Trends in acidic deposition mirror emission trends in the source area. For example, over the past 30 years in eastern North America, sulfate deposition has declined but nitrogen and ammonium deposition have remained relatively stable (Figure 3.3). Decreases in precipitation sulfate have coincided... 

We used the model PnET-BGC (Gbondo-Tugbawa et al. 2001) to compare current emissions reductions required by the 1990 CAAA with an additional 55% and 75% cut in emissions of sulfur dioxide, and 20% and 30% decreases in nitrogen oxides by 2010. These scenarios are based on the electric utility emission reductions embodied in bills recently introduced to the U.S. Congress. PnET-BGC considered changes in sulfur dioxide and nitrogen oxide emissions. It was assumed that base cation and ammonium deposition and climate would remain unchanged. 

Figure 4.2. Sulfate, nitrate and ammonium deposition in the study area from 1976 to 2002. Deposition was measured in bulk samples and may underestimate the dry component...

Sulfate, nitrate and ammonium deposition in the study area from... 

The amount of acidify produced by nitrogen depositions can then be summed with that due to sulphur depositions to give a value of total deposition of acidifying substemces from anthropogenic sources. The total acid load should include ammonium depositions, estimates of which can now be derived (EUassen et oL, 1988 Saltbones, Sandnes and EUassen, 1989). 

A) Adds. The ammonium salts of aromatic acids when acidified in cold aqueous solution will deposit the crystalline acid. 

Amides (except urea and thiourea), imides and nitriles, after the above alkaline hydrolysis, give derivatives similarly to those from the alkaline solution obtained from ammonium salts (p. 360). (A) If the original compound is aromatic, acidification of the cold solution deposits the crystalline acid. (B) The cold solution, when carefully neutralised (p. 332) and treated with benzylthiuronium chloride, deposits the thiuromum salt. 

Ammonia—Gas-Cured Flame Retardants. The first flame-retardant process based on curing with ammonia gas, ie, THPC—amide—NH, consisted of padding cotton with a solution containing THPC, TMM, and urea. The fabric was dried and then cured with either gaseous ammonia or ammonium hydroxide (96). There was Httle or no reaction with cellulose. A very stable polymer was deposited in situ in the cellulose matrix. Because the fire-retardant finish did not actually react with the cellulose matrix, there was generally Httle loss in fabric strength. However, the finish was very effective and quite durable to laundering. 

Ammonium Ion Removal. A fixed-bed molecular-sieve ion-exchange process has been commercialized for the removal of ammonium ions from secondary wastewater treatment effluents. This application takes advantage of the superior selectivity of molecular-sieve ion exchangers for ammonium ions. The first plants employed clinoptilolite as a potentially low cost material because of its availability in natural deposits. The bed is regenerated with a lime-salt solution that can be reused after the ammonia is removed by pH adjustment and air stripping. The ammonia is subsequentiy removed from the air stream by acid scmbbing. 

Dilution with water reverses the reaction, and heating the solution Hberates sulfur dioxide. Upon being added to a solution of teUurides, teUurium forms colored polyteUurides. Unlike selenium, teUurium is not soluble in aqueous sodium sulfite. This difference offers a method of separating the two elements. Like selenium, teUurium is soluble in hot alkaline solutions except for ammonium hydroxide solutions. Cooling reverses the reaction. Because teUurium forms solutions of anions, Te , and cations, Te" ", teUurium films can be deposited on inert electrodes of either sign. 

Copper etchants do not directly influence the electroless plating process, but are used merely to remove unwanted copper, and should not affect the deposit properties. The costs of waste treatment and disposal have led to disuse of throw-away systems such as chromic—sulfuric acid, ferric chloride, and ammonium persulfate. Newer types of regenerable etchants include cupric chloride, stabilized peroxide, and proprietary ammoniacal etchant baths. 

The most common plafing bath uses fluoride to complex the fin. A typical solution contains 45 g/L staimous chloride, 300 g/L nickel chloride hexahydrate, and 55 g/L ammonium bifluofide. It is operated at pH 2.0—2.5 usiag ammonium hydroxide temperature is 65—75°C and current about 200 A/m. The bath has excellent throwing power. Air agitation is avoided. The deposit is bright without additives. Anodes are cast nickel, and the fin is replenished by additions of staimous chloride. AHoy anodes of 72% fin have been used to a much lesser extent. Tia-nickel deposits are covered by ASTM (136) and ISO (137) specifications. One other bath based on pyrophosphate has appeared ia the Hterature, but does not seem to be ia commercial use. 

The precious-metal platinum catalysts were primarily developed in the 1960s for operation at temperatures between about 200 and 300°C (1,38,44). However, because of sensitivity to poisons, these catalysts are unsuitable for many combustion apphcations. Variations in sulfur levels of as Httle as 0.4 ppm can shift the catalyst required temperature window completely out of a system s operating temperature range (44). Additionally, operation withHquid fuels is further compHcated by the potential for deposition of ammonium sulfate salts within the pores of the catalyst (44). These low temperature catalysts exhibit NO conversion that rises with increasing temperature, then rapidly drops off, as oxidation of ammonia to nitrogen oxides begins to dominate the reaction (see Fig. 7). 

Other problems that can be associated with the high dust plant can include alkaH deterioration from sodium or potassium in the stack gas deposition on the bed, calcium deposition, when calcium in the flue gas reacts with sulfur trioxide, or formation and deposition of ammonium bisulfate. In addition, plugging of the air preheater as weU as contamination of flyash and EGD wastewater discharges by ammonia are avoided if the SCR system is located after the FGD (23). 

Rainfall at Rothamsted was first analysed for nitrate and ammonium about 120 years ago, but not very much was found. Between 1877 and 1915 the total deposition of nitrogen was 227kgha about 6 kgha per year on average. By 1990, measurements at four sites in south-east England " showed that the annual... 

Figure 2 Comparison of measured wet deposition of ammonium at Rothamsted, England with model estimates by Asman et al for regions whieh assume ehanges in emissions are only due to differenees in animal numbers. (Taken from Sutton et al ).

Figure 4-27. Ammonium nitrate salt deposits in the inlet of a nitrous gas axial compressor.

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