Scavenging ratio, mass

These results are similar to daily-averaged values reported by Barrie (18) for sites in eastern Canada (1978-1981). His mass scavenging ratios, multiplied by 890 (the ratio between the density of water and that of air at the 838-m altitude of Allegheny Mountain in order to match units), give the following averages for 4 remote locations ... 

Note that if there is no production or removal of i in the cloud, then C, 0 = C, int + C, cioud. The mass scavenging ratio defined above may vary from zero to unity. The number scavenging ratio FN can be defined as... 

These theoretical estimates are in good agreement with the high mass scavenging efficiencies measured in the atmosphere. Ten Brink et al. (1987) observed nearly complete scavenging of aerosol sulfate in clouds. The data of Daum et al. (1984) also showed that the bulk of the sulfate mass is incorporated into cloud droplets. Hegg and Hobbs (1988) reported scavenging ratios for sulfate of 0.5 0.2. 

If Cj Q is the concentration (in mass per volume of air) of an aerosol species in clear air before cloud formation (e.g., at the cloud base), and C/, cloud and C/ im are its concentrations again in mass per volume of air in the aqueous phase and in the interstitial aerosol, respectively, one can define the cloud mass scavenging ratio for species i, Fi, as... 

As shown in Table 6.9, (%p + fewo) is less than %,max for all of the example chemicals. Therefore, the continuous rain assumption is not producing unrealistically high wet deposition rates for these chemicals. The half-times for total wet deposition of the substances are benzene, 1.6xl0 h or about 180 years HCB, 3.7xl0 h or about 40 years Lindane, 431 h or 18 days B(a)P, 134 h or 5.6 days and nickel, 143 h or 6 days. Benzene and HCB are not efficiently removed from the atmosphere by wet deposition. Lindane and B(a)P are removed by wet gaseous deposition, and nickel by wet particle deposition. The 6-day half-life of nickel in the atmosphere represents the half-life for removal of particles by wet deposition in the generic scenario. This value is sensitive to the selected values for the rain rate and the scavenging ratio. The value of the maximum mass transfer coefficient for wet deposition corresponds to a minimum half-life in air of 38 h or 1.6 days. 

Cochran JK, Masque P (2003) Short-lived U/Th-series radionuclides in the ocean tracers for scavenging rates, export fluxes and particle dynamics. Rev Mineral Geochem 52 461-492 Cohen AS, O Nions RK (1991) Precise determination of femtogram quantities of radium by thermal ionization mass spectrometry. Anal Chem 63 2705-2708 Cohen AS, Belshaw NS, O Nions RK (1992) High precision uranium, thorium, and radium isotope ratio measurements by high dynamic range thermal ionization mass spectrometry. Inti J Mass Spectrom Ion Processes 116 71-81... 

This equation is particularly useful to derive apparent estuarine water mass ages (Fig. 6) because the term /em is removed. Using ( Ra/ " Ra) isotope ratios in this manner is based on the assumption that the initial ( Ra/ " Ra) activity ratio must remain constant. This conclusion is reasonable as the long-lived parent isotopes ( Pa and Th) have relatively constant activity ratios in sediments, and the intermediate Th isotopes ( Th and Th) are scavenged efficiently in the near-shore water column. The utility of Ra as... 

An optimum dose ratio of H202/03 has often been shown to be in a molar range of 0.5-1 depending on the presence of promoters and scavengers. Peroxide itself can act as a scavenger as well as an initiator, so searching for the optimum dose ratio is important. Enhancement of ozone mass transfer over that during ozonation alone can be expected in many cases. 

The possibility that the depletion of chloride in the marine aerosol is due to fractionation during the formation of sea-salt particles by bursting bubbles can be discounted. Laboratory studies of Chesselet et al (1972b) and Wilkness and Bressan (1972) showed no deviation of the Cl /Na+ mass ratio from seawater in the bubble-produced sea-salt particles. It may be mentioned in passing that bromide in marine aerosols shows a deficit similar to chloride, whereas iodide is present in excess. The latter observation is attributed to both chemical enrichment at the sea s surface and scavenging of iodine from the gas phase. A portion of iodine is released from the ocean as methyl iodide, which in the atmosphere is subject to photodecomposition and thereby provides a source of scavengable iodine. The process has been reviewed by Duce and Hoffman (1976). In continental aerosols, chloride and bromide are partly remnants of sea salt, but there exists also a contribution from the gas phase. 

Chemical separations may be specific for the analyte of interest (see Chapter 3), such as liquid or gas chromatography, or scavenging (such as by precipitation) to remove the major interfering substances. Addition of carrier, as practiced in radioanalytical chemistry to assist in purifying radionuclides, usually is not appropriate for mass spectrometric analysis. Such addition undermines the isotopic ratio measurements that are often at the heart of this procedure, and also overloads the system for ion generation and peak resolution (but carrier addition is used for accelerator mass spectrometry). Addition of tracers, known as isotope dilution, is often employed for yield determination (see Section 17.2.9). Interferences are distinctly different in radiometric and MS analyses of radionuclides, and may be the deciding factor in selecting one method versus the other. 

Both molecular mass and sulfate content of fucoidan played very important roles in the effects on the azo radicals 2-2 -azobis (2-amidino-propane)dihydrochloride-induced LDL oxidation (Li et al., 2006). The correlation between the sulfate content and scavenging superoxide radical ability was positive, the ratio of sulfate content/fucose was an effective indicator to antioxidant activity of the samples (Wang et al., 2008). 

Specific power and power density are also an important metrics, defined as the ratios of power delivered per unit mass or volume, respectively. For power sources that are not dominated in size by the storage unit, such as energy scavenging systems or high power application with short duration, the power density will define the scale of the device to meet a given power requirement. 

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