Sampling acid deposition

Serum and cerebrospinal fluid 206Pb addition and sample acid digestion lead isolation by ion-exchange, elution, and deposition onto platinum wire IDMS No data 80-120 Manton and Cook 1984... 

It is roughly estimated that there are more than 1,200,000 water bodies in eastern North America that are currently affected by acid deposition. A subset of these lakes has been sampled since early 1980s in order to monitor the changes in lake water chemistry induced by the declining sulfur dioxide emissions and wet sulfate deposition... 

Table 5 also reveals that the mean concentration of Pb in brown rice and leaves of 19 vegetable species from acid rain affected areas and non-affected areas are almost the same. On the other hand, the ratio is close to 1. This result indicated that acid rain does not influence the biological accumulation of Pb in brown rice and leaves of vegetables species sampled in Taiwan. Some studies have indicated that concentration of Pb in the crops was only affected when the concentration of Pb in the soils is higher than 500 mg/kg (Kabata-Pendias and Pendias, 1992). Sloan et al. (1997) also indicated that the relative bioavailability of biosolids-applied heavy metals in agricultural soils was Cd Zn >Ni >Cu Cr >Pb, for the soils 15 years after biosolids application. It is quite consistent with the results achieved by research of Chen et al. (1998). Thus, the phyto-availability of heavy metals caused by acid deposition followed the trend Cd >Zn >Cu Pb. 

Figure 10.6. Absorption of the C-H modes of a monolayer of 4-nitrobenzoic acid using SEIRA techniques. The curves are for increasing thicknesses of a silver overlayer. The inset shows the path of the infrared beam through the silicon total-internal-reflection plate. The sample is deposited on the two sides of the plate. (With permission from Ref. 23.)...

As demonstrated by papers presented at this Symposium, the increase of our knowledge about acid deposition in recent years has been enormous. The SURE project (Hidy, This Volume) demonstrated that huge field projects can be conducted with good quality control of samples, analyses and data. Kok, Tanner (This Volume) and others have developed highly sophisticated systems for measuring concentrations of many species, including the very important H2O2, in clouds and clear air with aircraft. In the area of mechanisms, we know that oxidation by -OH radicals is the dominant gas-phase reaction in the conversion of S02 to and sulfate (5). Furthermore, we know that oxidation in solution by is rapid and that by 03 and O9 (the latter catalyzed by metal ions or carbon soot) canoe important under some conditions (6 Schwartz, This Volume). 

Precipitation in the vicinity of Allegheny Mountain is about 107 cm per year (19), or close to the rate recorded in Table 2. If the ratio between deposition by rain and deposition to dew during the sampling period is also representative of the year, then it follows that the annual total acid deposited in rain is very roughly 60 times as great as that deposited to dew or in settled fogwater. 

Previously published data from two sites on the Wisconsin Acid Deposition Monitoring Network (2) and the University of Virginia site of the MAP3S Precipitation Chemistry Network (PCN) (3, 8) were used in the current study. The Wisconsin data were obtained for samples collected during the spring of 1984, and the Virginia data were related to selected samples analyzed during the summer of 1983. 

The effect of acid deposition on soil and eventually on land, water and the biosphere should also be studied further. The continuous observation of chemical deposition is needed with more suitable sampling sites and for more chemical components for these purposes. 

Determination of several atmospheric oxidant species is critical to understanding gaseous and aqueous processes leading to acidic deposition. Hydrogen peroxide has a high Henry s Law solubility and must be measured in gaseous and aqueous atmospheric samples to better understand wet deposition processes. In contrast, measurements of ozone and peroxyacyl nitrates (PANs) (and probably alkyl hydroperoxides and peracids) usually need to be made only in the gas phase due to their low aqueous solubility (14). 

Air pollutants, transport, 4 Air sampling—See Interstitial air sampling Aldehydes, determination in atmospheric samples, 299 Allegheny Mountain acid deposition and atmospheric chemistry, 28-36 deposition budgets for sulfate and nitrate, 33... 

Representative automobile poultice samples from Boston, Dallas, Detroit, and Montreal show a common chemistry in the northern states involving road salts and acid deposition. There were also significant amounts of chloride from dust control operations in Dallas. However, the different sites varied in the levels of ionic species and also in their proportions. 

It has been suggested some years ago that an acid deposition monitoring network should be set up in East Asia (Murano, 1997a, b). A uniform sampling and analysis protocol together with quality assurance/quality control (QA/QC) procedures has been proposed. This network is now in use and wonld prodnce more reliable data, which conldbe nsed to make more meaningful spatial and temporal comparisons. 

Figure 15o Acid deposition for the Den Helder, Witteveen and De Bilt sampling locations. Numbers in parentheses for De Bilt are annual amounts.

The Rollgen s group [9] reports the thermal desorption of [M + Alkah]" quasi-molecular ions from a electrically heated metal smface (wires or ribbons) for so-dimn alkah salts of carboxylic acids and mixtures of alkali halides with a crown ether, glucose and adenosine. With benzo-15-crown-5 the desorption of [M + Na]" ions takes place even below the threshold temperature for thermionic emission of alkah ions. Alkali ion attachment has also been performed by thermal desorption of thermally labile analytes such as saccharides, pharmaceuticals, peptides, steroids and their mixtirres. Bombick and Alhson [8] describe a desorption/ioniza-tion method where samples are deposited directly on thermionic emission materials (lK20 lAl203 2Si02) and heated within the mass spectrometer s source. Ions representative of the sample are formed. The proposed mechanism involves the gas-phase addition of emitted potassium ions to neutrals desorbed from the surface. 

Sulfuric acid (H2SO4) and nitric acid (HNO3) contribute the most to atmospheric acid deposition, though other acids, such as hydrochloric acid (HCl) and a variety of organic acids, also have been found in precipitation samples. Most acids are not directly emitted to the atmosphere instead, emissions contain acid precursors, typically oxides of sulfur (SOx) and oxides of nitrogen (NOx), which are oxidized further in the atmosphere to form sulfuric and nitric acids (Fig. 4.44). SO originate from... 

All electrochemical measirrements were carried out in sulphuric acid (1 M) at 25°C. The voltammetric experiments were performed using an Autolab-PGSTAT20 potentiostat with a three-electrode cell and a saturated calomel electrode (SCE) as a reference electrode (+0.245 V vs. normal hydrogen electrode, NHE). The catalyst sample was deposited on a rotating disk electrode (EDT 101, Tacussel), used as working electrode. All details, fiom sample preparation to experimental conditions, are extensively described in reference [9]. 

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